My furnance is driving me crazy

[Carol the Impaler]

Is this normal for a furnance? It's driving me batshit crazy.

When it kicks on, it has a piercing, metal on metal zzzzzzzzzzzzzzzznnnnnnng that drives me crazy. It is loud enough to wake me from sleep. It's horrible.

Made worse by the fact that the furnance runs constantly. It'll run for 10 minutes, shut off for two, power back up zzzzzzzzzzzzzznnnnnnnnnnng, run for 10 minutes, all day long. It does this if it is set on anything higher than, say, 65 degrees.

Lastly, the vents are these huge ole things and the forced air comes ROARING through them loud enough that I have to turn my tv up. Loud enough that when the furnance shuts off (for two minutes) I am so relieved because it's finally quiet in here!

It just shut off. In two minutes I'll get zzzzzzzzzzzznnnnnnnnnng, then the fan will start, then rrrrrrrrrRRRRROAAARRRRRRR!!!!!!!!!!!!

I get to the point where I just shut the damn thing off and put on my longjohns until I can't take it anymore. God, I fucking hate it.

Anyway, my landlord thought the constant running was a thermometer problem and installed a new one yesterday. Nope. Still running running running today.

He put some oil of some kind on.... something... in the furnance and that didn't help either.

Please God, tell me there is something I can do about this stupid furnance.

[ZenBeam]

I'm not a furnace guy, but I wonder if the blower is wired wrong, maybe for a different voltage than it's getting, causing the noise at startup and then running too fast.

Has it always done this? Was any work done recently? Or is this a new place for you and you don't know the history?

ETA: When it is running, is the air warm?

[John Mace]

Sounds like a problem with the bearings in the blower.

As for the heat problem, that could be anything from lack of insulation, older windows and doors, an undersized furnace, or maybe even a filthy air filter.

You'll need to get an HVAC guy to check things out. You can probably get a free estimate, just try to get someone you can trust.

[Magiver]

There shouldn't be metal-on-metal sounds. That's one problem. If the heat cycle is screwed up that's another problem. As for the air sound, that's a little harder to deal with. You could take off the return vent and line the area with sound deadening material. Usually that's a problem of too small a return duct. A good system would have 2 or more returns. The same goes for forced air side. A good system has multiple registers connected to it for each room.

[Joey P]

Assuming the zzzziiiinnnggggggg hasn't always been there, it sounds like one of the motors is dying (most furnaces have an inducer and a blower motor, the inducer comes on first). If the cycling started around the same time as the metal on metal noise, it's possible that what's happening is that the blower eventually binds up and the furnace shuts down. After a few minutes it tries to start up again.

Something you could try....Flip the switch on the t-stat from AUTO to ON. Assuming you hear the noise, we know it's the main blower motor making it. Does it run for longer then usual or does it stop after 10 minutes? It should continue running for as long as you have it set to ON. If it stops after a while then it could be binding up.

Also, the other possibility is that the squirrel cage (http://www.rclambert.com/supra/blower/blower%20squirrel%20cage.JPG) came loose. This would allow the motor axle to spin somewhat freely and make a god awful noise. This is pretty easily checked by popping off the bottom cover of your furnace and checking by hand. It shouldn't wobble and if you spin it by hand, it should feel like it's connected to a motor, not just hanging on a shaft spinning freely. You'll be able to tell. If you can't tell, go and set your t-stat to ON, go back to your furnace and hit the safety button that the access panel was holding down and see if you can tell if it's not on correctly (the motor will spin up, but the squirrel cage will sort of bounce around and take longer to get up to speed). If that's the case, it may be as simple as tightening a set screw with an allen wrench.

It's also possible that one of the blades on the squirrel cage broke off and is scrapping around inside the shroud.

[Joey P]

Another thing. While I'd take care of the noise before worrying about the cycling (since I'm guessing they're related and fixing the noise might very well fix the cycling), here's something else you can check.

Crank the heat way up. Turn the t-stat up by, say, 10 or 15 degrees. The furnace should not stop running until the new temp is met. If it still stops every 10 minutes, there's definitely a problem with the furnace (as opposed to the house insulation or the t-stat...though I suppose it could be a wiring issue). Again, I assume fixing the noise will fix the cycling. There's a sensor in the furnace that shuts it down if it overheats. It will overheat if the fan isn't spinning properly.

[Chefguy]

Good advice, all. I would concur with the blower fan motor bearings being a problem. I would add: when did you last change your return-air filter?

[wbeaty]

Not bearings.

Ever start up a car with a loose belt? Zsseeeeeek! The zing part is probably the metal ducts ringing, after the belt squeal has stopped. If the belt on your furnace blower is slipping, probably you can loosen an adjusting screw and pull the motor pulley tighter. If it's beyond the adjustment range, then it's time for a new belt.

[Snnipe 70E]

Could any of many.
Does the noise start when the furnace lights or when the furnace fan starts?

Does the furnace have an induce or forced draft fan?

Newer furnaces do not have belts.
Will not be wrong voltage. High AC voltage does not cause a motor to go faster (except series motors), it just lets the smoke out.

Fan bearings could be the problem.
Fan alignment .

To many possable problems to guess at on a forum.

[Carol the Impaler]

Hey, guys. Sorry to be returning to this thread after so long. To be honest, I've been so frustrated with my landlord about this issue that it made me feel disheartened to even come back to this thread. (That is to say, I've had to ask him more than once to address this problem and one other and that shouldn't be. Fix it, goddammit!)

So. He came and greased up the furnance. I don't know what he did beyond pulling stuff apart and greasing it or somesuch. After three days or so, the loud metal on metal sound was gone.

The problem continues to be the continuous cycling and the jet-engine-level roar of the air through the vents.

Here's what I know: the furnace will run for approx. six minutes and initially the air is warm. After five minutes or so, the air is cool, and the furnance shuts off. Takes one to two minutes for the ambient air temperature to drop a degree (so sayeth the thermostat) and the furnance kicks back on. Warm air for five minutes, then cool, then shuts off, etc.

This may be entirely because the house is poorly insulated and the heat begins to escape the minute the furnance shuts off. After many hours of this cycle, it stops and holds the temp for twenty minutes or so before switching on again.

Overnight, the temp is set to 60 degrees. The next programmed change is at 6:00 AM when it is supposed to heat up to 68. (This is a brand new thermostat, BTW. Installed the same day the landlord greased up the furnance.) The furnance starts at 5:30 (WTF?), and runs and runs and never reaches 68 before the next programmed phase at 8:00 hits. (Of course, the house generally drops to 59 degrees at, oh, 4:00AM and the furnance kicks on with a roar, wakes me up, ruins my sleep, shuts off, and starts all over and over. So then I get up and set it to hold to 55 degrees to keep it from coming on so I can sleep.) On weekend mornings, I will set it to hold at 70-72 degrees and it will run for three hours straight or more and never reach the set temp. If it's set to 70, it will hit 69 and stay there for hours. If it's set to 71, it'll hit 70 and stay there for hours.

Anyway, I know that I need to push my landlord on this, but if there's anything that springs to mind on what the problem is, it may help me get him to hire someone to fix it. I appreciate any ideas you may have.

[Joey P]

I'm not sure if you tried this, but I'll repeat my suggestion. Crank the heat waaay up. Add say, 15 degrees to the t-stat. It should not stop running until it get's there. If it keeps running in 6 minute shots, something is wrong with the furnace. I think that's the case, especailyl since you said that after a while it stopped for 20 minutes (that's probably when it hit the preset limit). My guess, assuming the motor is working okay, is that either A)an intermittent flame sensor problem (not likely based on the symptoms) B) Clogged AC evap coils (very possible) C) Bad limit sensor.
My guess would be for B or C.
Also, I assume you've checked the furnace filter, that could be the culprit as well.
See, the my guess is, that there isn't enough airflow, which means too much heat is building up inside the plenum/furnace and tripping the limit switch. The limit switch has thee settings. One setting says, "hey, there's some heat in here, kick the fan on" another say "uhh, somethings wrong, waaay to hot, shut everything down" and a third setting says "heats gone, shut down the fan" What typically happens is that the fire comes on, heats up the plenum and when it get's hot enough the limit switch kicks the fan on (this is so you don't get a blast of cold air at the beginning). When your house warms up, the fire shuts off but the blower stays on until the plenum get's rid of all the warm air so it doesn't go to waste (this is the cool air you feel at the end of they cycle).

If there's not enough airflow (clogged filter, bad fan, too many closed vents, clogged AC coils etc) the furnace can't move the heat out, the limit switch shuts down the furnace and the fan keeps spinning until all the heat is out.

As you may be able to guess, a faulty limit switch could also be the culprit.

Do you have central air? If you do, you might want to see if you can peel back or remove the access panel on the furnace plenum and take a look at the evap coils to make sure they are nice and clean. Check the furnace filter while you are there. Assuming that is in good shape and the motor is running properly. My next suspect would be the limit switch.
Actually, before that, I would check to make sure all the vents and returns as well as any inline dampers are all wide open.

ETA, one more thing. I don't know how much your landlord knows about furnaces so he may have checked this, but pull of the bottom panel of your furnace and find the circuit board, there should be an LED on it. It should be solid. If it's blinking, find out what that means. Either on the internet or a troubleshooting guide stuck to the panel you removed.

[Carol the Impaler]

Oh, man, Joey. You have a lot more faith in my abilities than I do. :) I will say it can't (I presume) be the filter. I change it on the first weekend of every month. They are most certainly not clogged beyond recognition.

Nevertheless, I will try to check things out as you suggest. Or, at the very least, spout your stuff off to my landlord so that it doesn't appear as if I am a total goob. I'm not running tests tonight, though, I'll be honest. Tonight is for wine and reading. ;) Thanks once again for your help.

[Joey P]

If you don't know much about furnaces, not big deal. But you can flip the furnace on and at least make sure you have a good amount of airflow coming out of all your registers. If not, that will narrow this down a bit.

Also, do you have central air?

Yeah, if you're not comfortable tinkering, there's only so much we can do (which is fine, it's hard to do 'blind' harder to do when the other person doesn't know what they're doing either), but we may still be able to narrow it down without using to much more then a screwdriver and a flashlight.

BTW, where's Raindog been during all this? He normally shows up in nearly any HVAC related thread. Honestly as much as I like being confirmed, I like being corrected as well when I'm wrong.

[Carol the Impaler]

I do have central air. Honestly? I am glad this problem will not involve me assessing anything called a squirrel cage. :)

Ok, it's 7:00 where I am. I just cranked the heat to 85. I'll be back.

[Joey P]

You don't have to let it get that hot. All I want to know is it starts and stops on it's way to 85. What it should do is run continuously until it get's there. If it starts and stops that's one thing. If it makes it all the way there in one shot and then cycles on and off it's something else entirely (but I don't think that's going to be the case).

If it's cycles on and off constantly like it's been doing before getting anywhere near 85, you can abort the test, that's all we need to know.

[Carol the Impaler]

Well, let's take a typical Saturday morning, for example. The thermostat is programmed to be at 60 degrees overnight, then at 6:00AM to fire up to 68 degrees. The furnance will kick on at 5:30AM and not stop until many hours later and not ever really hit 68 degrees. Then, after say three or more hours of running constantly, it will finally hit 68 degrees whereupon it shuts off. For two minutes. Then the temperature drops to 67 degrees and it kicks back on. For approximately six minutes. Hits 68, cycle starts over again. At about 2 or 3:00PM it finally stops this six minute cycle, and shuts off for 20 minutes or so at a time. Warm air at the beginning of the cycle, cool(er) air at the end. So much so that I catch a chill and know the furnance is about to shut off.

Gah, I turning the furnance down! I'm a boilin'! (Data point, the furnance has been running constantly for 23 minutes, so no short cycles.)

Hey, wasn't I supposed to be drinking and reading?? :D

Odd how I'm being gaslit by my furnance. ;)

[Joey P]

Okay, that's good. Running 23 minutes without stopping blows my busted furnace problem right out of the water. Again, good thing. Unless of course, your furnace is gaslighting you in which case we have yet a new problem to investigate. We'll come back to that later. Might need a priest.

What is the brand and model number of your t-stat? I'd like to have you make an adjustment to it.

[Carol the Impaler]

It is a Hunter 44110.

[Joey P]

Hold the up and down buttons at the same time until SPAN comes up. It should say "2". Hit the up button. I'm not sure how high you can set it, but I'd go for at least 4 or 6 based on what you've been telling me.

What SPAN does is tells the T-stat when to turn on and off. A setting of 2 means it goes +/- 1 degree. If it's set to 68. The heat turns on at 67 and runs to 69. At 4 it'll turn on at 66 and run to 70.

On most other T-stats this is called Swing.

At the least, this should slow down the constant on/off/on/off/on/off/on/off. It'll run for longer but it'll be off for longer as well.

Something else odd. You said that after it ran for 23 minutes it was sweltering (or is that from drinking (only kind of joking)) but earlier you said it takes hours to get from 60 to 68. It seems like one of those statements is wrong.
Eitherway, re-reading this, it seems that what's going on is that it A)takes a long time to get to the set temp and then b)has a hard time maintaining said temp once it's there. In which case, perhaps it is more of an issue with the house. You might want to look into some weather proofing. Check for drafts under doors. If there is a door to the basement close that. If there are drafts around windows see what you can do to seal them up etc....

[Johnny L.A.]

My propane wall furnace would howl a high note. It was driving me nuts. Turned out the gas orifice was too small. The repairman drilled it out and it's been quiet since.

[Carol the Impaler]

Hold the up and down buttons at the same time until SPAN comes up. It should say "2". Hit the up button. I'm not sure how high you can set it, but I'd go for at least 4 or 6 based on what you've been telling me.

What SPAN does is tells the T-stat when to turn on and off. A setting of 2 means it goes +/- 1 degree. If it's set to 68. The heat turns on at 67 and runs to 69. At 4 it'll turn on at 66 and run to 70.

On most other T-stats this is called Swing.

At the least, this should slow down the constant on/off/on/off/on/off/on/off. It'll run for longer but it'll be off for longer as well.

Ahah!! I bet you that is a big part of the problem.

Something else odd. You said that after it ran for 23 minutes it was sweltering (or is that from drinking (only kind of joking)) but earlier you said it takes hours to get from 60 to 68. It seems like one of those statements is wrong.

Nope, I swear on my eyeballs it's true. But keep in mind that the furnance has been running now since 2:30 when I got home from errands. After many hours it does hit and keep temperature better.

Eitherway, re-reading this, it seems that what's going on is that it A)takes a long time to get to the set temp and then b)has a hard time maintaining said temp once it's there. In which case, perhaps it is more of an issue with the house. You might want to look into some weather proofing. Check for drafts under doors. If there is a door to the basement close that. If there are drafts around windows see what you can do to seal them up etc....

Agree. Without question there are insulation problems here.

I think the Span resolution will make a big difference.

Wait. Only kind of joking??????

[Carol the Impaler]

My propane wall furnace would howl a high note. It was driving me nuts. Turned out the gas orifice was too small. The repairman drilled it out and it's been quiet since.

Yipes. That sounds... painful. And oddly... personal. :eek:

[Carol the Impaler]

Well, my Span only goes up to 3. So I'll see how much help that is. Also, just noticed I done spelt furnace wrong in my title.

[Batfish]

I'd be pretty annoyed at a thermostat that controlled to more than +/- .5 degF. A total span of 3 would drive me nuts.

Did Joey P's suggestion about thermostat span help? If it did it's good information but I suspect it's attacking the symptom not the problem.

The problem may be that the t-stat is not sensing the correct temperature. Is the furnace air blowing directly on the t-stat from the supply registers?

You mentioned at the beginning that the air "roars" out of the registers, perhaps the blower should be running at a lower speed.

[Joey P]

I'd be pretty annoyed at a thermostat that controlled to more than +/- .5 degF. A total span of 3 would drive me nuts.
On most T-stats the minimum +/- is 1 degF. Less then that and you would have a near constant cycling and would drive you more nuts then you realize. It also isn't good for the equipment as well as being less efficient.


Did Joey P's suggestion about thermostat span help? If it did it's good information but I suspect it's attacking the symptom not the problem.

I fully suspect that to be the case. I was just trying to offer a solution for major complaint which seems to be the cycling. The reason for the cycling still should be addressed though.

The problem may be that the t-stat is not sensing the correct temperature. Is the furnace air blowing directly on the t-stat from the supply registers?

Good idea, I hadn't thought of that. Carol is that a possibility? I'm thinking it's probably not since we had the furnace running for a solid 23 minutes, but it's worth walking over and checking into. Anything blowing on it? Is it in the sun (during the day)? Near any other heat sources like a stove, fridge, TV, computer, lamp, track light pointing at it etc?

[raindog]

Carol the Impaler what you described in post 10# is most commonly caused by a unit "cycling on the limits." I think Joey P is probably right.

Although many things (some of them uncommon) can cause this, I'd check the following:

1) Are the burners cycling off, or the fan? The burners and the fan are controlled in different ways. The fan may be running continuously, and therefore leaving you with the impression that the whole furnace, burners and all, are running, when maybe what's happening is that the burners are cutting in and out with enough rapidity that the blower never cycles off. It is common to hear that "my furnace never shuts off" , not realizing that the burners are indeed shutting off ("cycling on the limits") and it is only the blower that's not shutting off.

Unless you've done this, I would repeat Joey P's experiment, making sure to see if the burners-----not just the fan----stay on during the whole time the stat is calling for heat. It is possible that the furnace is overheating and the furnace stays warm enough to keep the blower on, but without your awareness it is periodically cycling the burners off due to an overheated condition.

The way to check this: Most manufacturers will design a "temperature rise" of 35°-70F. What that means is that the furnace will warm the incoming air (return air) 35-70 degrees. So......if your return air is 70, the air leaving the furnace will be 105-140. (assuming you're using natural gas) What is the temperature of the air coming out of the furnace? If it's hotter, that's usually an indicator of a dirty coil or anything that would inhibit air flow. If your air temp leaving the furnace is much more that 125ish, I'd suspect a furnace that's running hot and cycling on the limits. (which is unsafe, btw)

[raindog]

other experiences..........

Unless your furnace is 35+ it has no belt.

It usually isn't the stat. That doesn't keep homeowners of all stripes from changing them out. Its a logical assumption, but usually wrong.

Bearings going bad will usually whine, rumble, or make some other noise. Metal on metal is usually a squirrel cage that's rubbing against the fan housing. The set screw has come loose and the squirrel cage has shifted. Most modern blower motors have sealed bearings and need *no* oil.

Digital stats have different forms of "adaptive intelligence." What that means is that if you program it to be comfortable at 6:00 am, it will learn what time it needs to start to be comfortable at 6:00am. IOW, it isn't starting at 6:00 am, it recognizes it needs to be at set point at 6:00 am, so it will start earlier.

[raindog]

Other potential issues

1) A main high limit going bad. Maybe the furnace is not too hot, but the limit is weakening.

2) Where is your return air duct? Read the temperature at the return air register. Then read the return air at the furnace. They should be within 1°. If it is colder at the furnace than it is at the register you likely have some return air duct that is compromised/broken and you're picking up cold attic/crawlspace air. IOW, you're trying to heat the neighborhood.

3) A flame sensor. Pay close attention to the burners at start up. Do the burners ever shut off after 1-3 seconds? If so, you have a dirty flame sensor, an easy and inexpensive DIY fix.

[raindog]

can you tell us the brand and model of the furnace and stat?

[raindog]

Just throwing stuff on the wall to see what sticks.........

A "roaring" air noise may be an indicator of a dirty coil. Just as putting your thumb over the garden hose will cause greater velocity, a dirty coil may cause greater noise/velocity.

High air noises, coupled with high discharge air temperatures (greater that 120ish) makes me go looking for air flow issues.

[raindog]

It's Joey P's fault for my verbosity. He asked where I was. :D

All furnaces have a delay at the end of a call for heat to allow the furnace to deliver the last remaining heat content into the house. This delay is accomplished by shutting down the burners when the stat is "satisfied" and having the blower run another 90-120 seconds.

Theres 2 reasons for this: 1) It keeps the furnace cool. 2) You paid for the heat, so it makes sense to bring it into the home for your comfort.

However........that's only for 90 seconds or so. If its on long enough for you to perceive "cool air" that suggests to me a furnace that id cycling on the limit.

IOW, the stat is not satisfied, and there is still a call for heat. But a safety device has shut down the burners, and the fan continues to run. The fan cools the furnace down and Voila! the burners are allowed to come back on.

[Joey P]

Other potential issues

1) A main high limit going bad. Maybe the furnace is not too hot, but the limit is weakening. I learned about this in an odd way. I walked into work to hear. "Hey Joey, the furnace has been running for three solid hours." Well, since it was still a normal temp in the building I concluded it hadn't actually been firing for that long, so it must have been the fan. Some voltage testing and wire following led me to this odd thing with a dial and some buttons on it (what I later learned was the limit switch). Hmm, I thought...I'll bet if I [swift blow with a screwdriver handle] yup that did it...."ok" I announced proudly to anyone within earshot, "I need a new one of these brown things." (FTR, I knew what it was, I just like being overly vague).


3) A flame sensor. Pay close attention to the burners at start up. Do the burners ever shut off after 1-3 seconds? If so, you have a dirty flame sensor, an easy and inexpensive DIY fix.

Some sandpaper, may be all that's needed, but, a quick look at the circuit board should for a for a flashing LED should diagnose that and a host of other possible issues.

Like forgetting that your multimeter is in continuity mode and trying to test voltage and blowing a fuse on the circuit board :smack:

[Carol the Impaler]

I'd be pretty annoyed at a thermostat that controlled to more than +/- .5 degF. A total span of 3 would drive me nuts.

Did Joey P's suggestion about thermostat span help? If it did it's good information but I suspect it's attacking the symptom not the problem.

The problem may be that the t-stat is not sensing the correct temperature. Is the furnace air blowing directly on the t-stat from the supply registers?

You mentioned at the beginning that the air "roars" out of the registers, perhaps the blower should be running at a lower speed.

RE: the span suggestion. Has helped some, the cycles are longer. But the problem continues about the constant cycling.

As to the roar, I'll have to wait until my landlord is back to have him check the furnace out. Again.

[Carol the Impaler]

On most T-stats the minimum +/- is 1 degF. Less then that and you would have a near constant cycling and would drive you more nuts then you realize. It also isn't good for the equipment as well as being less efficient.


I fully suspect that to be the case. I was just trying to offer a solution for major complaint which seems to be the cycling. The reason for the cycling still should be addressed though.

Good idea, I hadn't thought of that. Carol is that a possibility? I'm thinking it's probably not since we had the furnace running for a solid 23 minutes, but it's worth walking over and checking into. Anything blowing on it? Is it in the sun (during the day)? Near any other heat sources like a stove, fridge, TV, computer, lamp, track light pointing at it etc?

Nope, not near any heat sources. Unless you count my burning anger. Heh.

[Carol the Impaler]

other experiences..........

Unless your furnace is 35+ it has no belt.

It usually isn't the stat. That doesn't keep homeowners of all stripes from changing them out. Its a logical assumption, but usually wrong.

Bearings going bad will usually whine, rumble, or make some other noise. Metal on metal is usually a squirrel cage that's rubbing against the fan housing. The set screw has come loose and the squirrel cage has shifted. Most modern blower motors have sealed bearings and need *no* oil.

Digital stats have different forms of "adaptive intelligence." What that means is that if you program it to be comfortable at 6:00 am, it will learn what time it needs to start to be comfortable at 6:00am. IOW, it isn't starting at 6:00 am, it recognizes it needs to be at set point at 6:00 am, so it will start earlier.

Roger. The grating metal on metal sound is gone since my landlord greased the furnace up. (I swear to God, I can't stop spelling that word wrong.) I wouldn't mind my furnace being all considerate of my needs at 5:30AM if it didn't have the godawful roar. In the meantime, I'll reset the program so start at 6:30.

[Carol the Impaler]

Other potential issues

1) A main high limit going bad. Maybe the furnace is not too hot, but the limit is weakening.

2) Where is your return air duct? Read the temperature at the return air register. Then read the return air at the furnace. They should be within 1°. If it is colder at the furnace than it is at the register you likely have some return air duct that is compromised/broken and you're picking up cold attic/crawlspace air. IOW, you're trying to heat the neighborhood.

3) A flame sensor. Pay close attention to the burners at start up. Do the burners ever shut off after 1-3 seconds? If so, you have a dirty flame sensor, an easy and inexpensive DIY fix.

Stupid question... are the return air duct and the return air register the same thing? What is the difference between reading the temp at the return air register vs. the return air at the furnace?

[Carol the Impaler]

can you tell us the brand and model of the furnace and stat?

The stat is a Hunter 44110. The furnace is a Tempstar N8MPN oro N8MPL (that's what the manual says, I can't find a model number on the unit).

[Carol the Impaler]

Carol the Impaler what you described in post 10# is most commonly caused by a unit "cycling on the limits." I think Joey P is probably right.

Although many things (some of them uncommon) can cause this, I'd check the following:

1) Are the burners cycling off, or the fan? The burners and the fan are controlled in different ways. The fan may be running continuously, and therefore leaving you with the impression that the whole furnace, burners and all, are running, when maybe what's happening is that the burners are cutting in and out with enough rapidity that the blower never cycles off. It is common to hear that "my furnace never shuts off" , not realizing that the burners are indeed shutting off ("cycling on the limits") and it is only the blower that's not shutting off.

Unless you've done this, I would repeat Joey P's experiment, making sure to see if the burners-----not just the fan----stay on during the whole time the stat is calling for heat. It is possible that the furnace is overheating and the furnace stays warm enough to keep the blower on, but without your awareness it is periodically cycling the burners off due to an overheated condition.

The way to check this: Most manufacturers will design a "temperature rise" of 35°-70F. What that means is that the furnace will warm the incoming air (return air) 35-70 degrees. So......if your return air is 70, the air leaving the furnace will be 105-140. (assuming you're using natural gas) What is the temperature of the air coming out of the furnace? If it's hotter, that's usually an indicator of a dirty coil or anything that would inhibit air flow. If your air temp leaving the furnace is much more that 125ish, I'd suspect a furnace that's running hot and cycling on the limits. (which is unsafe, btw)

A fan and a blower are the same thing? Forgive please, my ignorance, but I don't want to assume I undersand your questions.

Here's how it goes based on my observations just now at the furnace. The system powers up. Burners start one to two minutes later? Blower starts about a minute later? Burners stay on for a good ten minutes, then shut off. Blowers shut off two or so minutes after that. Then the whole system shuts off. IOW, the blower is not running constantly.

I don't have any kind of thermometer that could measure the air temp.

[Carol the Impaler]

I learned about this in an odd way. I walked into work to hear. "Hey Joey, the furnace has been running for three solid hours." Well, since it was still a normal temp in the building I concluded it hadn't actually been firing for that long, so it must have been the fan. Some voltage testing and wire following led me to this odd thing with a dial and some buttons on it (what I later learned was the limit switch). Hmm, I thought...I'll bet if I [swift blow with a screwdriver handle] yup that did it...."ok" I announced proudly to anyone within earshot, "I need a new one of these brown things." (FTR, I knew what it was, I just like being overly vague).



Some sandpaper, may be all that's needed, but, a quick look at the circuit board should for a for a flashing LED should diagnose that and a host of other possible issues.

Like forgetting that your multimeter is in continuity mode and trying to test voltage and blowing a fuse on the circuit board :smack:

The burners run consistently until they shut off at the end of the cycle. The LED flashes normal, according to the guide on the furnace (IOW, in a hearbeat pattern, dimmer then brighter, dimmer than brighter).

[Joey P]

Stupid question... are the return air duct and the return air register the same thing? What is the difference between reading the temp at the return air register vs. the return air at the furnace?

No, The registers blow air, the returns suck air. An easy way to tell is to hold a piece of paper up to the grate. When the furnace is running the returns will hold the paper up against the grate while the register will (as you might guess) blow it away. What Raindog is asking you to do is check the temp at one of the returns and at the furnace. I'll admit, I don't fully understand where he's going with this, but the easiest way is going to be with an infrared thermometer (in layman's terms a laser thermometer). Let the furnace run for a while, in face, I think you could just let the fan run for a few minutes. Check the temp of one of the grates. Now go to the basement and check the temperature of the sheet metal surrounding the filter area. Actually, even better (if you do have a laser thermometer), slide the filter out and check it. The sheet metal might be cold from the basement.

I think what he's suggesting is that if there's a big drop from the return grate to the basement that it's possible that your sucking in cold air somewhere and just making more work for your furnace and it's taking longer to heat the house. But I argue that unless it is a helluva a break this probably wouldn't be the case since A)once it does get to temp, the house isn't maintaining temp and B)newer furnaces pull outside air in by design.

OTOH (and maybe this what you were getting at) it could be making the noise.

[Joey P]

A fan and a blower are the same thing? Forgive please, my ignorance, but I don't want to assume I undersand your questions.

Here's how it goes based on my observations just now at the furnace. The system powers up. Burners start one to two minutes later? Blower starts about a minute later? Burners stay on for a good ten minutes, then shut off. Blowers shut off two or so minutes after that. Then the whole system shuts off. IOW, the blower is not running constantly.

I don't have any kind of thermometer that could measure the air temp.

That all sounds good.
Fan/blowers, yeah, usually the same thing. Few questions though. Does this furnace have two pieces of PVC coming out of it or one metal exhaust pipe that goes to a chimney or combines with a water heater exhaust.

Actually, that might answer my other question.

[Carol the Impaler]

One metal exhaust pipe that goes into the wall. The water heater pipe goes into the same wall but six inches below the furnace pipe.

[Joey P]

Nevermind, got my answer, it should have a single metal pipe coming out the top. Now, just to be clear, when you talk about the time between the system powering up and the burners coming on, assuming you are referring to another blower near the top of the unit that you can hear, right. That's the inducer motor. It comes online just before the gas starts (to induce a draft), runs the entire time the gas is on and the for a little while after the gas shuts off.

[Carol the Impaler]

To put it in terms of roar... Inducer motor starts, burners start, ROAR, burners shut off, ROAR continues for a few minutes, ROAR stops and there is blessed silence.

Am I losing you with the technical language? :D

Sorry to be such a inaccurate neophyte. But thank you for being so patient.

[Joey P]

To put it in terms of roar... Inducer motor starts, burners start, ROAR, burners shut off, ROAR continues for a few minutes, ROAR stops and there is blessed silence.

Am I losing you with the technical language? :D

Sorry to be such a inaccurate neophyte. But thank you for being so patient.

No but, (not that it was a concern since it was more or less ruled out earlier) inducer motor is ruled out as causing ROAR, as are burners. Leaves motor itself (along with squirrel cage) and ductwork.
And to go back to something I said earlier. There's a good chance that getting rid of the roar will get rid of the cycling. It's possible they are both caused by (or causing) low airflow.

[Carol the Impaler]

Gotcha. My landlord is out of town for the next few weeks, so it will be a bit before I can have him bring someone over. I don't think he's a furnace kinda guy. But at least I have a handful of symptoms and possible solutions for him to have a professional check.

[t-bonham@scc.net]

Gotcha. My landlord is out of town for the next few weeks, so it will be a bit before I can have him bring someone over. I don't think he's a furnace kinda guy. This is ridiculous.
Why should you have to wait weeks to get a heating problem fixed just because he's out of town? All the furnace repair people aren't out of town, are they? He can just call the HVAC company he uses and have them send someone over.

And why would the landlord have to be there anyway? He can't describe the symptoms, because he doesn't live there -- you would do that. If he's not "a furnace kinda guy", he won't be of much use in fixing this, he should leave it to a HVAC expert.

Contact your landlord, and tell him he needs to call in a HVAC professional NOW, not make you wait until he returns in 'a few weeks'.

[Carol the Impaler]

Yipes! Ok, I will, I promise! :eek:

:)

[Joey P]

If it makes you feel any better I just got back from fixing my parents furnace. It sounded like a washing machine that was ready to explode. Turns out some of the fins on the inducer motor squirrel cage came off, unbalanced the motor and it was wobbling something awful. Luckily she turned if off and it has a good set of shock absorbers so it didn't rattle the whole furnace apart.
$50 for the part, $5 for some caulk (since they didn't sell the gasket on it's own) and about 20 minuets of labor....and 13 friggen screws to get it out. Turns out a dab of caulk on the top of the screw makes it a lot easier to get a screw into a screw hole that's too far back to reach with your fingers.


:cool:


What's odd is that they have two furnaces, both scheduled to be replaced some time in the next few months. I'm surprised they didn't just take this opportunity to do it. Whatever, I like fixing things and it's their money.

[Carol the Impaler]

Yeah, I need to try to set a different expectation with my landlord. I'm trying not to be/sound annoyed with him (although I really am). But, yeah, I'm over-correcting into doormat territory because I don't trust myself to not be bitchy. Once again an opportunity to practice walking the middle path.

[Joey P]

Who pays the gas/electric bills?

[Carol the Impaler]

I do.

[Joey P]

That's what I figured. Otherwise, I was going to suggest you start cranking it way up to 85 or so and deal with the noise. Then turn it back down to something reasonable so you have some quiet for an hour or two. This would likely get his attention.

I think something you can do is to work on sealing up any drafts you can find. Get that plastic shrink wrap for the windows. Draft stoppers for the doors, keep the basement door shut (if there is one). If you have any unused rooms close the doors and shut the vents. Maybe even think about getting a space heater in the main part of the house. Even if you get the noise to stop, you're still likely losing heat to the outside...barring Raindog's theory of a leak in the return air ducting sucking in cold air from the attic or basement.

[Carol the Impaler]

Yep, I'll be taking care of sealing up drafts this week and getting a space heater. And I'll call my landlord.

[Joey P]

Those two things alone will probably make a world of difference. Make sure the space heater is the same space as the t-stat. Also, as you start sealing up the house, start in that area and work outwards for faster results.
If it's at all windy out, a book of matches (or a candle) will make it easier to find drafts around doors and windows. Also, if your house is old (and I assume it is). The electrical wiring is most likely all in conduit (as opposed to romex). If you put your hand near the outlets and switches you'll probably be able to feel a draft from there as well, make sure to get those sealed up.

[Carol the Impaler]

Yep, built in 1928. Seal the outlets and switches, too, huh? Maybe it would be cheaper to wrap myself in plastic sheet wrap. ;)

[Joey P]

Well, yeah, that would probably do the trick, but then you might want to run a small AC inside the plastic sheeting to deal the humility and we'd have a whole new set of problems.

As for sealing them up. A lot of this you can tell just by putting your hand near the offending areas (especially when its windy and/or really cold). Run your hand along the perimeter of exterior doors and windows, outlets, by the base of cabinets, under the window sills etc, you'll be able to tell where the cold air is coming in from. Start with those places then work towards the ones that you don't readily notice but based on things you hear about in the news or read about on the internet (do google searches for things like "weatherproofing your home" or "energy saving tips" and most energy company's websites have tips as well) you assume probably do leak.

[Carol the Impaler]

Good advice. You're very helpful. You should start a blog. No, seriously!

Ok, my ambien is kicking in. Time to go.

[t-bonham@scc.net]

Yep, built in 1928. Seal the outlets and switches, too, huh? Maybe it would be cheaper to wrap myself in plastic sheet wrap. ;)
Do NOT -- repeat NOT -- try to look that up on the Internet. You will get lots of sites that are not safe for work, and indeed, not safe to look at without nightmares!

But these things to fix drafts, etc. are pretty easy to do, and will make you a lot more comfortable, too. And they are mostly cheap. In fact, ones that involve permanent fixes to the house your landlord should pay for (or at least deduct from your rent). Don't expect payment for your labor, but the materials he should cover. So fixes like foam sealer or caulk around outlets & windows, weatherstrips (the kind that are attached permanently to the bottom of doors, not sand-filled bags in front of the door) and so forth are improvements to his property, and he should be willing to pay for them -- especially as you do the work of installing them. My family always did with our rental houses, and were happy to have tenants who did this.

[Carol the Impaler]

Huh, that's an interesting idea. I hadn't thought of that.

[Carol the Impaler]

Ok, so the furnace guy finally came out yesterday. Turned down the blower motor which took care of the roar. Cleaned the flame sensor which he said was really filthy.

Except that the on off on off hasn't changed. The thermostat is on the wall perpendicular to the opposite wall in the living room which has a big ole vent on bottom of the wall. The air blows warm until the burners shut off, then cold(er) and you can watch the temp on the thermostat drop... drop... one degree... then two... then the blowers shut off and four minutes later that... laaaast... final degree drop and it kicks back on.

Grrrrrrrrrrrrrrreat.

Tonight and last night it was taking about four minutes for it to start back up.

[capybara]

The last rental house I lived in had an ancient furnace (like, 1940) and when it was done heating something would kick back on after a short time for a few minutes-- I thought it was a touchy swing or whatever, but the equally ancient man I had look at it (pilot light issue) said that it was "venting" after the heating cycle. It's possible that it's something like that,

[Carol the Impaler]

Yeah, if you mean blowing out all the remaining hot air once the burners shut off? That's what the fine gentlemen of The Dope (you guys are all guys right?) taught me above is normal. (I have an entirely different need for venting after dealing with stupid furnace for a month ha.) My concern is that the last minute and a half the blowers are blowing out cool to cold air and that is making the thermostat think the air temp has dropped and hey time to turn back on! when what's causing the temp drop is the frickin' cold air coming out of the vent mere feet from the thermostat. And that the air shouldn't be THAT much cooler at the end of the cycle. (It's so much cooler that I can feel it as I sit here across the room about ten feet away. When the cold air starts, I know the furnace is going to shut off in five... four... three... ).

[Joey P]

Close the vent that's blowing on the T-stat or find some way to block the T-stat. Can you put a piece of furniture in front of the vent? Is the room set up in such a way that you could push a big chair (like a recliner) or a couch in front of it for a day (about a foot away) just to test out the theory? This way the room is still getting heat with the vent blowing directly onto the T-stat.

If that works, we can come up with a more permanent solution.
Depending on the style of grate over the vent it might even be as simple as getting one that blows the air in a different direction or putting a deflector over it (they sell them at home depot for about $5).
Otherwise, moving the T-stat around the corner isn't a big deal, it's just low voltage wiring with and small hole in the drywall/plaster.

[raindog]

Yeah, if you mean blowing out all the remaining hot air once the burners shut off? That's what the fine gentlemen of The Dope (you guys are all guys right?) taught me above is normal. (I have an entirely different need for venting after dealing with stupid furnace for a month ha.) My concern is that the last minute and a half the blowers are blowing out cool to cold air and that is making the thermostat think the air temp has dropped and hey time to turn back on! when what's causing the temp drop is the frickin' cold air coming out of the vent mere feet from the thermostat. And that the air shouldn't be THAT much cooler at the end of the cycle. (It's so much cooler that I can feel it as I sit here across the room about ten feet away. When the cold air starts, I know the furnace is going to shut off in five... four... three... ).

Ok......I know a little about this........

Your thermostat controls the burners, not the blower. The thermostat "calls" for heat and ignites the burners. At the end of the heating cycle----the point in which the thermostat is "satisfied"----the thermostat shuts off the burners.

You may ask then, "raindog, what's the deal with the blower if the thermostat doesn't control it?"; to which I say, "Good question, Carol the Impaler." ;)

If you have an older furnace the blower is controlled by a "fan/limit combination switch", a switch that is controlled by a temperature probe inserted into the furnace.

If you have a newer furnace it's done electronically via a circuit board that controls much of the furnace's functions. When it's done electronically, its strictly a timer: 120 seconds or so after the burners start the blower comes on, and 180 seconds after the burners shut off the blower turns off. The blower "lags' the initiation of the burners and the termination of the burners. (the times vary by mfr, and are approximate)

If you have an older furnace, it is common for the fan/limit combination to "stick"; because of old age/corrosion it "hangs up" and keeps the blower on too long after a heating cycle.

If you give us the make/ model number we can tell you what you have.

If its a newer furnace that uses an electronic timer, you have few options. They are generally preset on the circuit board and not adjustable. The solution then may be to set the fan speed on the motor to the lowest speed.

[Joey P]

Missed the edit window
Here's an example of a deflector
http://www.floorregisterresources.com/prodimages/sidewall%20decflector2.jpg
http://www.cornerhardware.com/images/5454.jpg

[Joey P]

Raindog, quick question for you. On newer furnaces, say installed within the last year or so. If you crank the T-stat up higher is the gas output higher as well? I tried to explain to two people the other day that the T-stat is simply a switch. It says "Hey, I need heat" and then later "That's enough heat, shut it down" but one person, who I generally trust, was telling me that with newer energy efficient furnaces that if the gap between what the room is and what you want it to be is larger that the furnace will have a higher output. It doesn't seem correct to me since, to the best of my knowledge, the t-stat has no way of sending the furnace this info. Am I wrong?

[raindog]

The Honeywell control (which is the most common but not the only one....) may look like this (http://www.inspectapedia.com/heat/FanLimitSwitch_L4064B_Settings.htm) or this (http://toad.net/~jsmeenen/blower.html) or this. (http://www.fixya.com/support/p524620-honeywell_l4064b2236_fan_limit_control)

[Carol the Impaler]

Ok......I know a little about this........

Your thermostat controls the burners, not the blower. The thermostat "calls" for heat and ignites the burners. At the end of the heating cycle----the point in which the thermostat is "satisfied"----the thermostat shuts off the burners.

You may ask then, "raindog, what's the deal with the blower if the thermostat doesn't control it?"; to which I say, "Good question, Carol the Impaler." ;)

If you have an older furnace the blower is controlled by a "fan/limit combination switch", a switch that is controlled by a temperature probe inserted into the furnace.

If you have a newer furnace it's done electronically via a circuit board that controls much of the furnace's functions. When it's done electronically, its strictly a timer: 120 seconds or so after the burners start the blower comes on, and 180 seconds after the burners shut off the blower turns off. The blower "lags' the initiation of the burners and the termination of the burners. (the times vary by mfr, and are approximate)

If you have an older furnace, it is common for the fan/limit combination to "stick"; because of old age/corrosion it "hangs up" and keeps the blower on too long after a heating cycle.

If you give us the make/ model number we can tell you what you have.

If its a newer furnace that uses an electronic timer, you have few options. They are generally preset on the circuit board and not adjustable. The solution then may be to set the fan speed on the motor to the lowest speed.

The furnace is a Tempstar N8MPN or N8MPL.

[raindog]

Raindog, quick question for you. On newer furnaces, say installed within the last year or so. If you crank the T-stat up higher is the gas output higher as well? I tried to explain to two people the other day that the T-stat is simply a switch. It says "Hey, I need heat" and then later "That's enough heat, shut it down" but one person, who I generally trust, was telling me that with newer energy efficient furnaces that if the gap between what the room is and what you want it to be is larger that the furnace will have a higher output. It doesn't seem correct to me since, to the best of my knowledge, the t-stat has no way of sending the furnace this info. Am I wrong?

You are right. (with a couple wrinkles)

The stat is a switch, like you said. It only knows that the switch has been thrown; that there is a call for heat.

The 2 wrinkles are these:

1) On a 2 stage furnace that is utilizing a 2 stage thermostat if the stat isn't satisfied within the time designed in the stats circuit board/ algorithm it will essentially throw a second switch----the second stage. ("W2" on most stats.) So....in that instance the stat could conceivably ask for more heat via a second stage terminal going to a 2 stage gas valve that a higher output on second stage.

2) The most advanced furnaces on the market today have a variable gas valve---called a "modulating gas valve." In those instances the gas valve is much like a variable speed blower; rather than one speed it has infinite speeds as it ramps up or down. With a modulating gas valve the ramping up or ramping down is not accomplished via the thermostat but the logic in the furnace circuit board. If the furnace is running for some specified period it ramps up or down based on run time. It is possible that some stats are integrated so that they are looking at the difference between space temp and set point, but in almost every instance it is the furnace that controls a modulating gas valve, not the stat. I would add that a modulating furnace is a great but expensive machine and represents a small percentage of all furnaces installed.

I say you're right.

[raindog]

Carol
I can check tomorrow to see how the fan is controlled and whether it is adjustable. I'm gonna guess you have a new enough furnace that the blower is controlled via a timer on the board.

[Carol the Impaler]

Thanks, Mr. Dog. Thanks, also, Joey. I have an non-standard sized vent so I'll head down to the Ace Hardware and see if they have something. I've just now closed the vent closest to the stat to see if that helps.

Hey, a drawer in my kitchen is broken. One of you guys want to take care of that?

[Joey P]

You are right. (with a couple wrinkles)

The stat is a switch, like you said. It only knows that the switch has been thrown; that there is a call for heat.
Good, just wanted to make sure I wasn't going crazy. This all started because one of my employees mentioned that it was cold. I went in back, checked, turned it up and told her I did so. She commented that it already felt warmer. I replied "Umm, no, it was running when you made the comment that you were cold, it's still running now" which eventually got to "It doesn't get hotter, it runs longer" blah blah blah, you've heard it a million times. Relaying the argument to someone later on, he told me I might be wrong. Maybe I was. I'll have to look at my furnace in the morning. Personally, I think my employee just thinks the air got hotter.


The 2 wrinkles are these:

1) On a 2 stage furnace that is utilizing a 2 stage thermostat if the stat isn't satisfied within the time designed in the stats circuit board/ algorithm it will essentially throw a second switch----the second stage. ("W2" on most stats.) So....in that instance the stat could conceivably ask for more heat via a second stage terminal going to a 2 stage gas valve that a higher output on second stage.

I know for a fact the T-stat is not a two-state t-stat, or at least that it's not wired as such. I wired it myself. In fact, I have a two stage t-stat in my house that you helped me wire (which due to another feature, I ended up not needing the two-state part)

2) The most advanced furnaces on the market today have a variable gas valve---called a "modulating gas valve." In those instances the gas valve is much like a variable speed blower; rather than one speed it has infinite speeds as it ramps up or down. With a modulating gas valve the ramping up or ramping down is not accomplished via the thermostat but the logic in the furnace circuit board. If the furnace is running for some specified period it ramps up or down based on run time. It is possible that some stats are integrated so that they are looking at the difference between space temp and set point, but in almost every instance it is the furnace that controls a modulating gas valve, not the stat. I would add that a modulating furnace is a great but expensive machine and represents a small percentage of all furnaces installed.

I know the motor doesn't modulate since when we installed it (in summer) it was so ungodly loud we couldn't talk over it so I changed the speed for the AC from High to Medium. I'm kind of curious about the gas valve though. I'll have to look at it in the morning.[/QUOTE]

[Carol the Impaler]

Hey, BTW, thanks again for mentioning the issue with the blower motor speed. Turning that down has made a ton of difference in my enjoyment of my home. It's so nice and quiet in here!

[Joey P]

Thanks, Mr. Dog. Thanks, also, Joey. I have an non-standard sized vent so I'll head down to the Ace Hardware and see if they have something. I've just now closed the vent closest to the stat to see if that helps.

Hey, a drawer in my kitchen is broken. One of you guys want to take care of that?

Most of the deflectors I've seen are two part things the slide in and out to fit multiple size registers.

[Carol the Impaler]

By God, it's that kind of engineering miracle that may just save me a shit-ton of money on my gas bill!

[raindog]

I seem to remember that all modulating gas valve furnaces also have variable speed blowers.

That would tend to make sense since a variable modulating output gas valve would need to be synchronized with a variable speed blower: when the gas valve modulates (ramps) up the variable speed blower needs to ramp up to meet the demand of the higher output of the gas valve.

So I thin it's a safe bet that if the furnace doesn't have a variable speed blower it likely doesn't have a modulating gas valve either.