Questions tagged [furnace]

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.

204 questions with no upvoted or accepted answers
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110 views

Furnace keeps going into lockout

My furnace has been going into lockout after several retry cycles. This happens about 30% of the time when we turn on our heat. We had a repair person who came over quite a while ago, and tested all ...
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1answer
1k views

Furnace Connect G Wire

I have a dual energy electric/oil furnace that is wired to a thermostat with 2 wires R and W. I don't have any AC. Inside the furnace there is a switch relay to control the fan but it is not connected ...
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60 views

Why isn't my furnace igniting?

I noticed cold air from my Carrier 58SS furnace. The main burners were not lighting. The pilot flame was strong, but yellow. When I tapped on the gas valve, the pilot shut off. I removed the pilot ...
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2answers
37 views

Installing c wire in older furnace

I just installed a nest thermostat and need to hookup the c wire inside the furnace. I read where you need to connect the c wire to the secondary wire on the 24v side of the transformer. There are 2 ...
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0answers
55 views

Blower turns on before furnace ignites

I have not relocated/changed the thermostat or had any work done on my furnace. The fans turn on well before the furnace starts giving off warm air, which blows a lot of cold air into my home. I have ...
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0answers
16 views

Safe to install humidifier above furnace gas vent?

I'd like to add an AprilAire 600 bypass humidifier. I plan to install the humidifier on the supply plenum, and the bypass duct on the return air. The gas vent coming off the furnace is type B. ...
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124 views

Humidifier not keeping up with HRV

I just moved to an new (for us) house and we seem to not be able to keep the humidity up in the house. The house comes with a Heat Recovery Ventilator (HRV) that in the winter runs all the time on low ...
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29 views

Goodman motherboard with broken/cut wire

I have 2 Goodman furnaces with the same issue. In the middle of the motherboards there is a plug with a red wire and blue wire, and a white wire loop - pictured. My white looped wire is broken or cut. ...
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2k views

Thermostat not getting power (Nest E74)

I replaced an old Honeywell thermostat about a month ago with a Nest thermostat. Friday Nest started displaying an E74 error. I have two furnaces and two outdoor units, one for upstairs and for ...
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77 views

Rheem RGDG unit turns on w/thermostat off, blower come on and inducer motor switches off and on

I've having a problem with my rheem model rgdg-10nbrjr The air conditioning works, turning it on at night it blows cold air and the house indeed gets cold. However the furnace unit itself ...
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37 views

Garage Furnace Runs Only 45 seconds at a time

I have an older Janitrol Moffat furnace in my garage. It was converted sometime in the past from propane to natural gas. It takes quite awhile for it to heat up enough for the fan to kick in and once ...
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100 views

Replacing a motherboard on a Carrier 8000VS Furnace

Hi guys, I am trying to finalize the wiring of my new carrier motherboard. I have about four more wires to connect and the new motherboard is slightly different than the old one. The pictures I’ve ...
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105 views

Converted Oil Furnace to Natural Gas - Fuel Smell Issue

This weekend, we had our fuel oil furnace replaced with a natural gas one. The oil furnace broke near the end of the winter and we were waiting for a deal to kick in on a whole new furnace + A/C unit. ...
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779 views

Installing Ecobee3 with Trane Furance

I am installing an Ecobee3 and have found that, while the common wire exists, it is not connect to the furnace. The wiring schematic for my specific furnace can be found in this PDF There is no ...
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1answer
10k views

Goodman gas furnace limit switch opening, blower only runs with a/c

I apologize in advance for some of my incorrect terminology. My father has a 2004 Goodman GMH80904BN gas furnace with a/c. The a/c has functioned properly all summer here in Ohio, we have recently had ...
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893 views

Constant cold air from vents with new downdraft furnace

Replaced with newer, high efficiency furnace and cold air constantly coming out of vents (except when furnace running). It's like the downdraft is totally free flowing and when windy outside very ...
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3k views

How can I reduce noise from an air handler unit in an open closet?

How can I reduce the noise from an air handler unit? I have a Goodman AR42-1 air handler unit in an open closet. The setup looks like this: When the air handler activates it sounds like this: ...
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1answer
7k views

how to change furnace filter (bottom return) for Lennox G43UF

I have a Lennox G43UF furnace and I am not sure if I need to have both a filter for a side return and bottom return. If I do (which sounds logical), where would the location of the bottom return ...
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0answers
241 views

Would a radiant barrier help stop this heat transfer?

Using my nifty thermal camera, I discovered that my furnace closet's combustion air duct (visible in this question) is getting really hot when the attic heats up, and then (being sheet metal) it ...
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0answers
1k 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 ...
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0answers
335 views

Why won't my condenser turn on when I run my heat pump?

I have a York Affinity condenser. When I run my heat pump, I expect it to turn on somewhere in the cycle but it doesn't. It generally does this once a year. The usual fix is to cycle the power of the ...
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54 views

For a smart thermostat, where do I attach the C wire to my furnace?

I know I've seen several questions out there about getting a C wire for a smart thermostat, however after all the research I've done and people who have given me guidance so far I have still had no ...
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2answers
76 views

Hooking up AC compressor to an old Lennox furnace

I'm trying to connect an ac compressor to an old Lennox G12Q3-110-3 furnace. Tried it a couple of ways and can either get the compressor to turn on or the furnace fan. Not both. Any ideas on how to ...
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2answers
53 views

I need a C wire connection for my new Glas thermostat

I have 3 wires(red,white,and green) going to my thermostat. I’m replacing my old thermostat with a new one the requires a C wire connection. The 3 wires goes to my Honeywell aquastat. The white goes ...
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26 views

Flame sensor keeps getting dirty?

My father replaced his furnace about a year and half ago. His flame sensor every 2 weeks to month stops igniting and he will have to take it out to clean it. He's brought in furnace guys numerous ...
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61 views

What wires do I need to connect to get Aprilaire 600 working?

I just replaced an old Aprilaire with a new 600 model. I wired up all the previous wires to the corresponding spots on the new controller, but there are still open spots and when I turned power back ...
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66 views

C Wire - Williamson Furnace/Honeywell Thermostat

I'm trying to install a new wifi thermostat, but am a little confused. I have 5 wires, but none are connected to the C in the thermostat, as seen below: Additionally, when I trace the thermostat to ...
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131 views

Connecting fresh-air damper to Lennox furnace OR replacing timer with new smart thermostat

We replaced a 20-year-old furnace with a new Lennox furnace and added air conditioning. The new system is still controlled by the 20-year-old Honeywell Chronotherm III thermostat. The furnace had (and ...
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41 views

Furnace setup switches seem to be in the wrong position

My furnace (Bryant 926TA) has to arrays of setup switches. I am particularly concerned with SW1-3 (off in my picture) and SW1-4 (on in my picture). The manual calls SW1-3 Low Heat Rise Adjustment and ...
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24 views

Intermittent pilot light furnace giving up before igniting pilot light (Lennox G20 WhisperHeat)

Background: I have a Lennox G20 WhisperHeat furnace (on natural gas) with an intermittent pilot light. The unit is around 25 years old, and has functioned flawlessly until recently. The problem: ...
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27 views

An unsteady flame when furnace is warming up

When my furnace has warmed up the house and turns off for a bit it struggles to turn back on. While the furnace is cold I can look into the combustion chamber and notice the flame is acting like ...
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14 views

Fixing sub-optimal Tempstar furnace vent installation but can't find part numbers

I have a Tempstar N9MSE0601714A furnace with 2" PCV vent pipes (that mate to 2.5" pipes). Whoever installed it didn't fallow the installation manual and I'm also reducing the number of ...
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1answer
166 views

How can I close a gap between ceiling drywall and a furnace flue?

My gas furnace is located in my laundry/utility and is normal(~80%?) efficiency with a Type B Flue. It goes up through the drywall ceiling into my attic(1 story) and out the roof and I verified that ...
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170 views

Carrier Furnace Pilot light and Main Burner Flames out when main blower kicks in

Carrier furnace runs for about 3 minutes. Hot air comes out from vent for a minute or so it then turns off and kicks back on after 1 minute or so. I cannot find the model of the unit as the tag is so ...
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88 views

Gas furnance runs blower and signals false flame

My 7yo-ish furnace is running blower excessively. It reports (according to manual) a "false flame sensed" (5-blinks). This is NOT, however, in response to the start of a heating cycle. To ...
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2answers
45 views

HVAC / Furnace Evaporator unit in attic leaking cold air

We have an A/C (and heat) unit in the attic with force air ducts going to the ceilings in the rooms. I was in the attic today when the A/C turned on. I felt cold air come on my leg when I was near the ...
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1answer
258 views

Run Only The furnace fan

I have an old unit that has no control board. It works with a sequencer. (Coleman 3500A816) is it possible to wire it up to to be able to call only the blower to come on and not the heat as well? !
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30 views

Fan Only operation not working - gas forced air furnace

So i followed online guidance to enable "fan only" mode for my forced air gas furnace, Essentially that was to connect the "G" terminals on the t-stat and the furnace board. Seems simple enough, but ...
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56 views

Part on furnace making scratching noise

This spinning part on my furnace (not sure what the part is called) is making this scratching noise. When one section of the part hits the area behind it, it makes that noise. Any idea how I can ...
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1answer
59 views

How can we connect a smart thermostat to our heating system, which is a gas furnace and wood fireplace?

We have a KozyHeat wood fireplace connected to our older gas furnace. The idea is that the furnace serves as a fan when the fireplace is hot, or will use gas to heat the house if the fireplace is cold....
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1answer
1k views

Sticky black liquid coming from Furnace / AC Unit

I have this sticky black liquid slowly leaking from my gas furnace / ac unit. I called an HVAC repairman and he wasn’t sure what it was. He said he thinks it’s an old drip pan made of tar (not sure ...
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23 views

Gas furnace ignites but then makes large knocking sound

My gas furnace will ignite, but after the pilot goes on for a moment it creates a large periodic knocking sound over and over again instead of the fan starting. I have my suspicions, but I wanted to ...
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464 views

Thermostats with or without variable temperature differential (swing)

I am looking at replacing my thermostat, and don't really need or want one with geosync. I am thinking of the honeywell RTH9585wf. Currently I have a lux that is not wifi but programmable. It ...
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54 views

Water Dripping From HVAC Furnace PVC

I have 2 PVC pipes coming out of my TRANE gas furnace. Today I noticed that one is dripping water from the top. Picture attached. Its a slow drip. What could this be?
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1answer
36 views

Furnace Inducer Whirrs on and off before igniting, works when I tap circuit board

My furnace gets the signal from the thermostat, then about half of the time, the inducer motor whirrs on and off over and over. Sometimes it runs continuously without ever lighting. When I open it up,...
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188 views

Lennox G51MP shutting down with Primary/secondary switch fault

I have Lennox G51MP-48c-090-06 ~14yrs old, starting up for first time this season. It is throwing error code: Primary or secondary limit switch open. Unit shows normal operation when powered up and ...
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2k views

Only getting 15-16 volts from Furnace R and C

I recently purchased a smart thermostat. Because it needed a common wire and I only had a 3 wire setup, I ran a new thermostat wire to my furnace. However, I now get only 15 volts (inconsistently, ...
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42 views

Furnace blower cutting in and out during A/C use

Backstory: I fired up my air condition for the first time this season (single family house) and felt lukewarm air coming out of my ducts. When i went outside i saw that the condenser was not turning ...
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0answers
28 views

Furnace Pilot Flame ON constant but Main Burner never kicks in

I own an older furnace (Armstrong EG6F80DC12-6 -- natural gas, forced air, single stage, Honeywell S8600C Continuous Re-Try Module, VR8204A Gas Valve w/ Pilot Burner / Igniter-Sensor). It has been ...
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1answer
65 views

Adding split AC to a Dayton oil fired forced hot air furnace

I'm trying to add split central air to my Dayton oil fired forced hot air furnace, mod # 3E268A. The manual clearly says it can accept this but the terminal block in the unit only has (4) lugs. TT and ...

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