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.
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,
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… ).
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.
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.
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?
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:
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.
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.
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.
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?
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.
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)
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.
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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!
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.
