The furnace is part of an HVAC or central heating system used to generate heat. Typically this is done with gas, a heat pump, or an electric element. For hot water and radiator based heating, use the boiler tag.

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How to wire multiple thermostats

I would like to have two thermostats controlling a single furnace. However I'm not 100% sure how I would need to wire everything to achieve the correct effect. Assuming a thermostat simply acts like ...
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3answers
5k views

How do I wire a humidifier without a 24 VAC IN terminal?

The instructions for the humidifier I'm installing says to connect the humidistat wiring to the two terminals "marked 24 VAC IN". My furnace doesn't have terminals marked that. I have R,C,W,Y.G. Am ...
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0answers
113 views

How should I shut down a woodburner that is attached to an electric furnace for the night?

I have a Monarch Add-A-Furnace wood burner connected by ductwork to my Armstrong Air electric furnace. I use the wood burner when it gets really cold outside, but shut it down at night because I do ...
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4answers
4k views

Why would a furnace overheat with a standard density filter?

Some time ago I found my furnace (gas, forced air, downdraft) was getting stuck on, blowing cold air. I could reset it, but it would happen again after a while. After calling out a service man, I ...
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1answer
133 views

Legal requirements regarding 100% asbestos duct work [closed]

I am renting a condo. After starting the heater, dusty air came out of the registers, so I called out a company to clean the ducts. They verified the ducts are 100% asbestos and cannot be cleaned. ...
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0answers
1k views

Why is my furnace limit tripping?

My furnace is tripping the high limit. It is a Downflow Payne 90+ have replaced the limit switch. I pulled the blower door off and checked all vents to ensure they are open and it still short cycles. ...
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1answer
149 views

Can I install a flow through humidifier on either side of the duct?

I was about to install a Wait6000 whole home humidifier when I hit this snag in the plan. On page 3 of their manual (PDF), it says the cold air return duct must be at least 10" wide. The diagram ...
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3answers
511 views

Should the fill line be removed when decommissioning an old oil tank?

So, I have a contractor decommissioning my old 650-gallon oil tank. There is a 3" metal tube coming out of the ground from the tank that is what I believe to be the receptacle used to fill the tank ...
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2answers
8k views

What size breaker and wire do I need for central air conditioning?

I am getting ready to hang drywall in my basement but before I do that, I need to run wire from the main panel upstairs to the future location of the central AC furnace through the basement ceiling ...
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2answers
265 views

How do I close this hole in the HVAC vent?

What's the best way to close up this hole in the venting leaving the hvac? Would foil tape be sufficient? Right now it bleeds out hot air into the basement in the winter, and cold air in the summer. ...
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1answer
1k views

Furnace won't adjust to thermostat setting

I have a 2007 Trane furnace that has been working the AC all summer just fine. With the cooler weather, when I turn on the heat and set the thermostat to 72 degrees, the furnace comes on but heats the ...
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4answers
1k views

Are 5" thick filters for furnace/Central AC still available?

My furnace/AC was installed about three years ago. It uses 16" X 25" X 5" filters. The problem is when I try to find a replacement at my local home center: at Lowe's, Home Depot, (you name it), I ...
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1answer
477 views

How do I maintain an 80% efficient natural gas furnace?

I have an 80% efficient gas furnace at my house, that is seemingly working well and is configured with an air conditioner. What preventative maintenance should be done to it, and at what interval? Is ...
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2answers
3k views

lennox furnace not working pilot light on but burner doesn't start

lennox furnace, model # G20Q2E-75-C1, serial #6392H32332, pilot light lights, blower motor turns on, burner doesn't burn
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2answers
2k views

Can I piggyback a thermostat with a C Wire hookup on a furnace?

I'm trying to install a new thermostat that needs a C wire hookup. There are currently 4 wires running from the thermostat to the furnace, none of them are a c wire. When I look at my furnace itself ...
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1answer
179 views

Should I use a quick or gradual 90 in my flexible A/C ductwork?

To elaborate a bit more. If you are running an 8" duct off the supply, would you do a quick 90 degree towards the destination or do a gradual 90 degree? I would guess a quick would be better because ...
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2answers
2k views

Can I remove the fresh air supply that is attached next to my furnace?

It looks like my gas furnace is already vented but I'm not sure. There are two white pipes from the top of the furnace that are vented outside. The furnace is a Trane XR90. We have cold winter climate ...
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1answer
950 views

How can I prevent water from entering through water heater/furnace exhaust vent?

I have an exhaust vent in my basement (Amerivent Type B) which takes the exhaust from my gas furnace and water heater goes out the basement wall, and up my chimney. A little bit water is coming in to ...
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1answer
202 views

Replacing Oil Furnace with Heat Pump

My wife and I would like to remove the older oil heat from our home and replace it with a heat pump. We currently have an Amana central air conditioning unit (3 ton), and an oil furnace in the ...
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1answer
15k views

Why is water collecting in the base of my furnace?

I changed my filter the other day and noticed a pool of water in the bottom of the furnace, below the filter. The humidifier has been off so that's not the issue. I removed the furnace panels and see ...
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1answer
2k views

Why is the circuit breaker for my furnace stuck in the off position?

The breaker for my furnace is stuck in the off position. We were away for the winter and had someone shut it off, and now the breaker won't turn on at all. We shut off the thermostat upstairs thinking ...
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1answer
117 views

Can a non-expandable filter be used in place of an EZ flex furnace filter?

My Carrier furnace has the EZ flex filters (16x25x5). These come with the plastic end caps that fit on the expandable filters. Can a regular filter, non expandable, of the same dimensions be used as ...
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7answers
4k views

What should I do with old furnace filters?

I seem to be stock piling used furnace filters, are there any uses for these things once the furnace is done with them? It seems a shame to throw them out; given that I change them once a month, ...
2
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1answer
308 views

What is a quieter alternative to gas forced air heating?

My small 1BR apartment has an old gas furnace that works great, but costs my landlord too much to insure. He plans to install gas forced air, an in-unit upright furnace. I'd love to suggest a ...
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1answer
116 views

What to look for in a new furnace

I've recently been told that my furnace, which is about 20 years old, is on it's last stretch and that I should consider replacing it now rather than waiting for it to fail - potentially at a very ...
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2answers
5k views

How do I build a firewall around my furnace/water heater?

I'm in the planning stage of finishing my basement. I'd like to section off the furnace and water heater, and am assuming that I should fireproof that section of the build. What's the best way to go ...
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2answers
679 views

How is a high altitude natural gas burner different?

What is the difference between high altitude natural gas burner and conventional low altitude gas burner and why high altitude natural gas burner are needed?
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1answer
322 views

Should I relocate the HVAC unit in my attic?

I have had a couple of estimates to replace our HVAC system and one contractor says he would relocate the system to a more central location in the attic. One says there is no need to relocate. There ...
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3answers
12k views

If I turn off the breaker to the Gas furnace will the pilot light go out?

I need to turn off the breaker for the furnace but am afraid this will turn off the pilot light to my gas furnace & I don't know how to relight it. Are any special steps necessary to prevent ...
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2answers
269 views

How do I interpret my furnace clearance diagram?

My brother-in-law and I are going to be finishing my basement. We just got the permit from the building inspector. When they returned my plans there was a note that told me to make sure furnace and ...
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2answers
2k views

Why is my furnace blower coming on so early in the ignition process?

Alright, I installed a new furnace a few months ago and have begun to notice an issue with the blowers. When the furnace first starts up, the exhaust blower should turn on to expel gas, then the ...
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2answers
487 views

Can I move my furnace room ventilation intake closer to my furnace?

I live in a 3 story townhouse with a garage in the basement. Off the side of the garage is our furnace room. The ventilation and exhaust for the furnace goes to the roof. For ventilation (air coming ...
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4answers
17k views

Does lowering the blower speed of a forced-air furnace lower its efficiency?

My gas furnace has two options for the blower speed: MED, and MED-HI. It had been set on the higher speed, but that was too harsh, so I lowered it to the slower speed. Does that have any impact on the ...
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2answers
14k views

What does a Summer/Winter switch on furnace air ducts do?

On some of our furnace ducts, there is a switch/valve for Summer/Winter or S/W. What does changing this switch/lever accomplish? Can bad things happen if I forget to switch it? Bonus question: ...
4
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1answer
607 views

How can I unbend a bent furnace filter slot?

I recently bought a new home. When going to change the furnace filter, I couldn't get the original furnace filter out of the slot at the last part of the filter (where the cardboard border is). Since ...
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0answers
451 views

Why is my furnace blowing hot air outside?

So I have been having trouble heating my home. I noticed today that there is a vent blowing hot air outside. It is not the return, chimney or venting. Any ideas other that the builder thought we ...
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0answers
274 views

How can I provide my furnace with outside combustion makeup air?

I cut a 6" opening in an insulated door into the utility room then installed a 6" metal duct with a plastic exterior vent cover. I put 6" insulated flexible duct on the interior stub and let it hang ...
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1answer
6k views

Can a washer and dryer be next to a water heater?

I have a GE gas dryer (DSXH47GGWW) that is currently next to an exterior basement wall. I'd like to move it to the opposite wall (shared with the crawl space) right next to the water heater next to ...
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2answers
18k views

How can I determine why my furnace is not blowing enough heat?

During a cold spell last week when temperatures got down to -23f (-31C) my furnace started showing issues with blowing enough air and the air was not very warm. Last winter it did not have any issues ...
2
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1answer
950 views

How can I stop my house from waking my wife up every day in the winter?

I'd like to preface this post with the fact that I'm a complete diy amateur. I may say stupid things, or things that make no sense. Please feel free to correct me as I'm always open to learn. So, ...
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3answers
12k views

Why is my Lennox g40uh series furnace not turning on?

I have a Lennox g40uh series furnace and it just stopped working today. I can reset the furnace and can see that on the control board both LEDs (green and red) are blinking together which indicates ...
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0answers
970 views

What's causing my draft inducer to stay on?

I have a new, 3-year old, high-efficiency, gas furnace in my home. I recently realized that my draft inducer, which normally kicks on before the burners and before the main blower, is not stopping. ...
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3answers
7k views

What's causing the rumbling sound when my furnace kicks on?

I have a new, 3-year old, high-efficiency furnace in my home. Last year it started making a slight whining noise that was audible during the very first stage, before the blower motor started. No ...
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0answers
282 views

Are w1 and w2 both energized during a second stage heat call from the thermostat?

Short version: does two-stage thermostat always close W1 circuit when it closes W2 circuit, or they might be closed independently? Long version: I have two-stage furnace, currently connected to older ...
2
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1answer
396 views

Will I see any performance gains if I reconfigure my thermostat to control the second stage of my 2 stage furnace?

Our furnace is a two stage one that was installed last year (a Bryant 80t). When it was installed, it was installed with a thermostat for a one stage furnace. This appears to be because this model ...
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1answer
3k views

Why does my pilot light go out continuously?

My furnace pilot light keeps going out. The furnace will come on and heat up to the degree set on my thermostat, then the pilot goes out and the furnace will not come back on. Could the thermostat be ...
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2answers
251 views

Furnace control board - interchangeable?

A few months ago, I had someone working on my outdoor a/c unit, and he accidentally shorted out the control board in the furnace (it's a Goodman gas furnace GKS91155DX). He replaced the board, and the ...
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7answers
3k views

How can I audit my furnace?

I want to keep track of when my furnace is on, with an eye to reducing how much energy I use to heat my house. I could compare it with weather data (temperature, wind speed, precipitation). I could ...
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4answers
660 views

Is it expensive to switch from an 80% to a 90% efficient furnace, to comply with the new mandate?

I'm told by some HVAC companies via mail flyers and websites (example) that it may be very expensive to retrofit new PVC pipes to update an 80% efficient furnace to a 90% one. Therefore, the logic ...
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1answer
1k views

why won't my furnace turn off once it reaches the desired temperature

I have a moncrief furnace and replaced the thermostat but the furnace will not cut off once it reaches the desired temperature. What could be wrong?