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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Goodman GM100 Failure to recycle

Our Goodman Furnace Model GM100 Serial# 9412063230 will start up and run but will not recycle after initially satisfying the thermostat. If you wiggle the gray,(ground), wire on the gas valve, it ...
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34 views

my furnace fan stays on even when at temperature

I recently installed a 2nd generation NEST thermostat. I'm not home very often, but I was paying particularly close attention to the furnace after installing this thermostat and I noticed that the ...
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20 views

Why does my furnace only heat up to a certain temperature?

Why does my furnace only heat up to a certain temperature, then it stops heating the home? My programmable thermostat is set to go up to 70 degrees (to heat the home) and for some reason when it ...
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15 views

Can a full expansion tank prevent the furnace from going on?

Woke up this morning and the furnace wasn't working. The furnace is relatively new, and there appears to be a small amount of water dripping from the top of the expansion tank. I know that the ...
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14 views

Why won't my furnace turn off after replacing the igniter?

My igniter on my Frigidaire furnace went out. before replacing it I reset a limit switch that set off. I changed the ignitor and everything works, however now the thermostat is not shutting it down at ...
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21 views

Replaced Thermostat, Furnace worked for 1 cycle now blows cold

Hello I just replaced my old White-Rodgers thermostat because it just wasn't working consistently (sometimes it would turn on the furnace, but mostly it wouldn't). I swapped it with a White-Rodgers ...
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26 views

Why won't my my furnace stop running unless I shut it off at the breaker?

I can't get my furnace to shut down unless I turn off the breaker. Why is this happening, and how do I fix it?
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29 views

Why would a gas furnace shut down after 20-30 seconds?

I have an 18yo Lennox gas furnace (Modle 23G89). It starts and runs for 20-30 seconds then shuts off. The light blinks in a steady state- no code. Then I removed the filter to guarantee a clogged ...
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27 views

Lennox G40UH takes a long time for the heat to come on

The digital thermostat lights up with "HEAT ON" but it takes the furnace up to an hour to kick start. Once it does, it puts out heat. We set it to 69 here in Michigan with the outside temp at Zero. ...
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29 views

How to clean carbon build-up on Honeywell whole house air purifier made of aluminum?

Bought a house recently that has a Honeywell F300 whole electric house air purifier/cleaner. The cell's aluminum fins have a black baked-on dust that I expect is preventing the unit from working as ...
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34 views

What type of furnace vent pipe is this?

I need to extend my furnace vent pipe up 2 foot above the ridge of my roof to comply with IBC. So I need to couple this pipe somehow and extend it up. Any idea what type of pipe this is and how I ...
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42 views

Testing the exhaust of a natural gas furnace?

I recently had maintenance performed on my natural gas forced-air furnace. During this maintenance, the technician went outside and used an electronic handheld device with a wire-attached probe to ...
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27 views

Identify/troubleshoot this millivolt furnace valve

I have an old millivolt gas furnace that's stopped working. The pilot stays lit fine and the thermopile generates about 360 millivolts, and there's no problem at the thermostat (checked voltage and ...
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78 views

Why would only 1/3 of my registers be blowing warm air?

I have a Coleman gas furnace in a wall space in my house which somehow shares the blower on my a/c unit on the roof because it turns on when furnace is called to start, though it does bump up after a ...
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124 views

Can I use the T terminal in my furnace as the C for a Wifi Thermostat?

I've read many posts on this, and believe I know what to do, but want to make sure. My furnace (a Lennox G14 Series) does not have a C terminal which needs to be connected to the C terminal in my new ...
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279 views

Could wind be causing my high efficiency furnace exhaust to back up into the house?

I am Toronto based, and just installed a new high efficiency furnace (York YP9C 080 model) in November. Later on I smell odor in my house when the heat started. It is more apparent when it is a gusty ...
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213 views

What could be causing my furnace burners to fire up, then shut off due to partially open door?

I have a 10 year old Carrier gas furnace that keeps shutting off every 24-48 hrs. First I thought it might be the flare sensor but then I checked the bottom door and it wasn't completely closed. I ...
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3k views

What could cause a Trane furnace to not start heating?

I have a newer (2007?) Trane XL90 (model: tdx2b080a9422aa)forced air gas furnace. The problem I am having is the burner and fan will not start. The thermostat is set at 67 degrees and shows it is ...
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557 views

Why is my furnace blower running at low speed?

My Payne gas furnace (PG8UAA 42091) automatically shuts down after it lights and burns for two minutes. It then gives a 33 fault code. I've done some research and some testing and have narrowed the ...
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75 views

Furnace reset problem

I have a new Goodman high efficient furnace model number GMH950703BXAG1. And this is the problem I'm having now: Turn on the furnace power (after ~1 hour off) Turn on the thermostat with Temp ...
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360 views

Why is my new high efficiency furnace blowing cold air sometimes?

Why does my new furnace high efficient Payne furnace blow cold air,not constantly but at least 3 different times in a day, my thermastat is set on auto but when the weather is cold outside it will ...
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223 views

Can I relocate my furnace exhaust?

When my new furnace was installed, the vent was put outside the house next to landscaping bushes. It has killed one of my bushes. It used to be vented up to my roof and out. Can I move this outside ...
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129 views

How can I install a furnace register in a kitchen-cabinet toe kick?

I'm planning to install new kitchen cabinets. I'll be covering up the kitchen's existing sidewall diffuser with new cabinets, so I'd like to relocate it to a new register in the toe kick of the sink ...
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114 views

Why won't a NEST that shares control of a furnace with a conventional thermostat turn on the heat?

I have three floors in my home. The bottom floor has its own gas furnace and the 2nd and 3rd floors share another gas furnace. Everything was working great until I added a NEST to the first and ...
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114 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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170 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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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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466 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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1k 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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268 views

How can I clean out the pressure switch port at the inducer housing on a Lennox G40UH furnace?

I have a Lennox G40UH(x) furnace, but the gas does not ignite, because water may have entered the system while raining, or the the pressure switch port at the inducer housing has just to be cleaned. ...
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2answers
225 views

Oil-fired furnace sight window repair

I have an 20+ year old oil burner and a tankless boiler/furnace. There is a small round (2-3" diameter) window above the burner that lets you see the flame, I assume as an aid to tuning the burner. ...
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90 views

Can you vent electric dryer into furnace return?

I've got an electric dryer currently vented outside: Behind the door to the right is our heat pump furnace: I was thinking about, during the winter, venting the dryer (properly filtered for lint) ...
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1k views

How do I connect a WiFi thermostat to my furnace's primary control?

I would like to install a Honeywell WiFi controlled thermostat to connect to a Honeywell R7184U primary control. My question concerns the "C" wire. The R7184 has the terminals labeled 1, 2, 3 and 4 ...
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3answers
81 views

My lennox furnace has no filter

I searched for 30 minutes, and I could not find the furnace filter, is it possible to install/build a filter slot? my whole family got allergy after turning on heater this winter. Thank you! Lennox ...
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3answers
26 views

Can't select some temperatures with the thermostat of my furnace

I have a problem with the thermostat of my furnace. This problem is wired but I'll try to explain it as clearly as possible. When I turn the button of the thermostat, some temperatures can't be ...
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2answers
512 views

Should I replace my Pressure Reducing Valve?

A few weeks ago, my oil-fired water boiler started continuously leaking water out of the pressure release valve on the top of the unit. I know this is leaking steadily because it drains into a 5gal ...
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58k views

How can I test whether my furnace issue is the limit switch or the thermostat?

I suspected this issue during the winter and confirmed it now in the summer. Regardless of the temp in my home, the blower motor runs non-stop. In the winter this must have been causing my home to got ...
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2answers
49 views

Can I remove a furnace compartment vent that's obstructing roof repair?

There are two vents going up to our roof, one is the normal vent from the furnace exhaust straight up to the roof. But right next to it there's a second vent pipe, a little larger and single wall. ...
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2answers
52 views

HVAC system setup

I have a builder building me a home right now and we had agreed to set up two separate heating and cooling systems for the first floor and second floor of the house. I raised the issue the other day ...
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190 views

How do I connect my whole house humidifier to my furnace?

Connecting Desert spring Humidifier to the furnace: Do I eliminate the 24V transformer that came with it? The furnace Keeprite has the the electronic board says Humidifier W1 and C. where can I ...
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103 views

Condensation at roof, down outside of furnace/water heater vent. What is happening?

I am getting condensation dripping down the outside face of my furnace vent at the roof. I think I know why this is happening I'm just curious how to remedy it. There is a cast iron exhaust pipe that ...
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1answer
181 views

Does the pilot flame of a gas furnace stay on for the duration of a heating cycle?

I was looking at my furnace a couple of days ago and I notice one thing: there is something red hot there where the spark igniter and the thermocouple assembly is. I can hardly see it and I am not ...
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4answers
124 views

Is it safe to use an HVAC system even though the duct wrap contains asbestos?

In our rental house the furnace ducts are very dirty. We brought an expert to clean it, but he said he just won't do it because the tape around the ducts (in the attic) is probably asbestos. After ...
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1answer
47 views

If flame sensor will affect Motor assembly's functionality of furnace? How does that work? [closed]

I have two Air conditioning company. A is the self-hired for my A/C, and B is assigned by home warranty company. This summer, the technician with A came out for an annual maintenance on both A/C and ...
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1answer
2k views

gas furnace pilot light is lit,,won't produce heat, making a clicking sound,,,

my gas furnace isn't producing heat the pilot light is on and it's making a clicking sound what can I do? I've tapped the flame rod.
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1k views

Why does my furnace drip bucket fill up so frequently?

We have an oil furnace that heats the house using a two-zone hot-water circuit, and also acts as an on-demand hot water heater. There is a pipe coming off the collection of pipes coming out of it that ...
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203 views

How can I prevent my furnace exhaust pipe from freezing?

My furnace keeps on turning off because my air intake freezes. The reason it freezes up is because my neighbors exhaust vent blows directly on it. What can I do to prevent this?
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251 views

Would a failing igniter cause my furnace to blow cold air?

I noticed tonight my furnace was firing up, but not actually blowing out heat. I turned the thermostat down so it was no longer triggering it, let it sit for a couple of minutes, and then turned it ...
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139 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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3answers
6k views

Why isn't the spark gap lighting the pilot on my furnace?

I've got a Carrier 58GS natural draft furnace, which has a spark gap for igniting the pilot. Unfortunately, the spark gap has not been successfully doing its job. The spark clicks away as the gas ...