My furnance is driving me crazy

Factual Questions
1

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.

2

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?

3

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.

4

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.

5

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 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.

6

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.

7

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?

8

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.

9

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.

10

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.

11

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.

12

Oh, man, Joey. You have a lot more faith in my abilities than I do. :slight_smile: 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. :wink: Thanks once again for your help.

13

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.

14

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

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

15

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.

16

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?? :smiley:

Odd how I’m being gaslit by my furnance. :wink:

17

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.

18

It is a Hunter 44110.

19

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…

20

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.