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 do I reduce the noise from my forced air furnace?

We recently had a new forced air furnace and return installed. The unit works great, but the return (which is in an adjacent closet to the furnace closet) is quite loud. What are some solutions I can ...
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35 views

Is it normal for the burner in my furnace to turn on and off during a single heating cycle?

During the heating time when the furnace is running to reach the temperature ask for, the burners will run for 3.5 to 4 mins.than shut off for 1 min. Then turn on again.it will do this until temp. is ...
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49 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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44 views

Carrier 60,000 BTU 92% Furnace vs Carrier 40,000 BTU 95% AFCU Furnace

I have about 900 finished square feet in my house, and I'll eventually be adding another 200 or so finished sq/ft in my basement. I'm looking to get my furnace replaced and have been quoted two ...
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19 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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23 views

What could cause the furnace to not come on after airing out the house?

Turned the furnace system off and manually turned fan on at the thermostat to air out the house after staining woodwork. Now the system is turned back to Heat and Auto Fan but will not cycle on. The ...
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40 views

The hot water is working but the radiators will not heat up!

We have a Utica Boiler model number SFH4150WT and we are receiving hot water but the radiators do not heat up!!. We tried bleeding the radiators, they only heated up a little bit but after about 5 min ...
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28 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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35 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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59 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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22 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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56 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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40 views

Possible to check NEST system compatibility by looking at current thermostat model?

I'd like to replace my Honeywell CT87A thermostat with a Nest thermostat. I see that Nest has a page to check system compatibility. Is it possible to identify if my system is compatible without taking ...
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44 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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91 views

My furnace cycles once, then won't ignite again. What could be wrong?

My furnace is not working properly. I shut down the whole electricity and also the switch on my furnice and waiting a few minutes to turn all back on. It will heat up the house and turns off ...
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45 views

How do I calculate how long a furnace has to work to compensate a given temp drop?

I am trying to understand the dynamics of heating a home after the furnace size was calculated. Say you have a 60000BTU furnace to heat a 2000 sqft home. At the beginning of the heating season you ...
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102 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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66 views

furnace blower motor vibration when working hard

A few weeks ago my furnace developed a vibration that can be heard throughout the house. If I remove the side panel of the furnace or if I remove the filter, the vibration goes away. My theory is ...
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108 views

Can I connect an electronic air cleaner to the 24v terminals of my furnace?

I have a Goodman GKS90904CX furnace and looking to install an Electro Breeze Air Cleaner. The air cleaner needs an R and C 24v terminal for power or a power outlet with the supplied transformer. I ...
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39 views

Do natural gas furnaces have internal breakers?

I rent a house with a natural gas furnace. The furnace was not working at the beginning of this winter, and so we called the landlord to fix it. The landlord hired a repair man, who came and noticed ...
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24 views

train xl 80 unit fires up then shuts right off

i have a train xl80 furnace. When it calls for heat the draft inducer fan turns on and then the burner fires up for a short time then shuts off then it starts all over again.I am thinking its the ...
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20 views

Limit switch is good but no heat

I am getting a 4 blink indicator saying my limit switch is bad. I tested the switch and it is good. What else could it be?
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129 views

What could cause a flame sensor to stop working so frequently?

Over a year ago after a month in our new house, we came back one evening to a cold home and after some googling, I found out that the flame sensor was dirty and the furnace was starting the flame and ...
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110 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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40 views

How do you troubleshoot a baseboard heater that is not heating up?

I have baseboard heat and we are not getting heat on one room. Can't bleed air from the baseboard itself. How do I troubleshoot the issue?
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53 views

wiring furnace draft inducer fan

I replaced a draft inducer fan on my furnace, the two wires in the furnace that connected to the old fan are black and white. The wires from the new fan are both black. How do I know which to connect ...
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68 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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50 views

Closing off heating ducts

We have a natural gas furnace that currently heats our entire 2400 square foot home. We plan on putting in a rental suite in the basement which will require closing up all the duct work into the suite ...
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18 views

I have a slantfin hot water furnace ,it goes on then shuts off every 2 min until. It reaches the set temp

Slantfin furnace goes on and off every 2 min until it reaches set temp
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28 views

Main burner will not light, but the pilot is ok

I have an old Heil unit 100,000 BTU, it has been working fine up until Tuesday night. The pilot light is on. I replaced the gas control valve, I know it has limit switches should I replace them all or ...
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114 views

Gas furnace air is cooler (but NOT COLD) during bitter cold days - why?

I have a Lennox central gas furnace. It is only about 3 years old, and was on the very high end of the models available in terms of energy efficiency and such. I sprung for a more expensive model ...
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71 views

Blower fan speed selection

I am reading a book about HVACs (not finished yet,I might find my answer down the road) and they say that you can increase the speed of your blower (well ..you can adjusted) to obtain the airflow you ...
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1answer
46 views

A professional to test asbestos safety in furnace ducts

We live in a rented house with an old furnace duct system (probably 1960's). There is asbestos-containing duct-wrap all around the ducts, and it starts to crumble in some places (it's located in the ...
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1answer
108 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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54 views

Very old furnace- I need a technician to inspect it-What would be a good check up list?

First of all you should know that this is about a 25 years furnace that is very simple and that if nothing is wrong with the heat exchanger it should last forever since, IMHO, the parts are very ...
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73 views

How do I check if this furnace switch the blower to second speed

My furnace is overheating and I suspect that the blower motor does not go into high speed. Can anybody say what is the cause or how can I check if it indeed switches to high speed? Here is the wiring ...
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39 views

With registers fully open I have unbalanced air flow upstairs vs downstairs

Upstairs the airflow is OK Downstairs I have 4 registers. Three out of four have very weak air flow while the fourth one is blowing like hell Is the problem in the furnace or in the air ducts?
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50 views

Asbestos in my furnace closet - should I get rid of it?

I have a home built in 1958 with a closet inside the house that contains the furnace. When the house was constructed this closet was lined with asbestos as a safety measure. How dangerous is it for my ...
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1answer
59 views

What temperatures are normal in this area of my furnace?

Please see the attached picture and pay attention to the "temperature dial" in the inset With the current settings the gas burner cycles like this -limit temperature 200F -at that temperature the ...
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1answer
199 views

Where do I connect the C wire in my furnace?

I am upgrading my thermostat to a Nest, and would like to add a common wire. My current furnace controller doesn't have a C terminal, but the current thermostat wire has 2 unused wires (black and ...
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1answer
109 views

What is wrong with my gas furnace?

Note: the below was solved. It was a loose wire between the controller and the gas valve (the white wire on the diagram) This is about an old UltraMax Olsen HCS2 81AD gas furnace it looks like this ...
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4answers
99 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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52 views

What is the smell coming through my HVAC system?

If I leave the furnace fan always running for an extended period of time (to circulate and filter the air), when the central AC turns on there is a not-so-fresh smell that is emitted through the ...
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1answer
69 views

Is there any way to stop the air leak through my furnace without compromising its operation?

My house has an 80% efficiency gas furnace in an interior mechanical closet with the return air path below the furnace and through a grille under the closet. However, since the furnace is not a sealed ...
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1answer
271 views

How can I connect a humidifier to a Goodman dual fuel heating system?

Purchased a dual fuel goodman system with CTK04 comfortnet thermostat. The thermostat installtion guide shows wiring of a humidifier to the (2) Hum terminals on the furnace IFC. My furnace model is ...
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26 views

How do I get the main furnace blower to come on when the wood burner furnace calls for heat?

I need to know how to wire the gas furnace blower to come on when the wood burner's blower kicks on.
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1answer
169 views

What could be causing vibration in my furnace?

I have a vibraton in furnace only when flame is lit. Blower motor seems fine. Is this vibration normal? Recently replaced inducer motor. Heat exchanger has been replaced once. Does not appear to be ...
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2answers
463 views

Where's the C terminal on my boiler control?

The new thermostat I purchased doesn't run on batteries, and needs 24 volt power. I have only a red and a white wire connected between the boiler and the thermostat, but there is also a third, unused ...
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40 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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70 views

What could cause my old gas furnace to keep cutting out?

I have a old gas furnace that keeps cutting out. It turns on and the when it hits the temp it turns off and then when it turns on it will not give it gas. It will just sound like it blowing but no air ...