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.

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11 votes
2 answers
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How do I identify the C terminal on my HVAC?

How do I identify the C terminal on an HVAC, furnace, or boiler? If the terminals don't have a screw labeled C what should I look for on the wiring diagram? What steps should I take if a wiring ...
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10 votes
1 answer
47k views

How many wires can be connected to the C terminal at the furnace?

I'd like install a new Wi-Fi thermostat. The old one didn't have a C-wire but luckily there is an unused wire on both sides (one coming out of the wall and one at the furnace not connected yet), so I ...
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6 votes
8 answers
18k views

How to Lower the Ouptut of Oversized Furnace

Questions I would like to lower the output capacity of my furnace if possible. How can I do this? Is it worth doing, or should I just live with it? Is there an easy way? Some ideas: replace burner ...
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4 votes
2 answers
25k 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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4 votes
4 answers
25k views

Why is my furnace blowing cold air?

My HEIL 7000 natural gas furnace has stopped working what are the most likely causes, and how to verify faulty parts? Normal operation routine Thermostat sends "need heat" signal. Exhaust blower ...
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4 votes
5 answers
171k views

Why does my pilot light keep going out?

My furnace pilot light keeps going out so I changed the thermocouple. Now the furnace will come on and heat up to the degree set on my thermostat, then the pilot light will go out and the furnace will ...
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2 votes
2 answers
10k views

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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18 votes
10 answers
31k views

Do thermostat-controlled, auto-adjust HVAC vents exist?

The residential forced-air HVAC systems I have seen are controlled by a single thermostat in one room. One has to manually adjust the vents in order to adjust the temperature in other rooms. Is ...
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5 votes
5 answers
51k views

Adding a C wire to a new Honeywell WIfi Thermostat

I am trying to install a new Honeywell touchscreen WIFI thermostat and need to add a C wire to my terminal inside the furnace (using the help found at How can I add a "C" wire to my ...
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7 votes
6 answers
150k views

Why does my furnace need frequent power resets?

I have a NOMA Programmable thermostat attached to my furnace. The set point is usually around 21 degrees, and the room temperature is reading around 17 degrees. The furnace is not coming on. However,...
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5 votes
2 answers
13k 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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4 votes
5 answers
75k views

Why would my Goodman gas furnace start but not stay on for more than 2-3 minutes?

I've got a problem with my 15 year old Goodman furnace. It starts w/o problem, inductor begins working, hot surface ignitor lights up and ignites the gas. Then the main blower starts working and the ...
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6 votes
4 answers
20k views

How can I avoid cold rooms due to combustion air intake?

I have a newer split level house (2006) with unfinished basement. The natural gas furnace is on the lower level in a utility room that is also laundry and bathroom. There's an enormous 8 or 10" pipe ...
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6 votes
2 answers
5k views

Can an electric dryer be next to the gas furnace?

I intend to relocate my washing machine and electric dryer within the basement. The dryer will then be about 2 feet from the furnace. Is that OK?
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3 votes
3 answers
10k 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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  • 31
3 votes
2 answers
750 views

After blowing heat the fan won't stop, continue blowing cold air for prolonged period of time (30+ min)

Not always, but often the furnace continue blowing cold air after blowing heat. It may blow cold air for more than 30 minutes. Under this conditions I also see the error code (8 red flashed) "Ignition ...
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0 votes
4 answers
2k 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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  • 149
10 votes
8 answers
5k 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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10 votes
7 answers
130k views

How much energy will continuously running a furnace fan use?

We have a bi-level (tri-level? There's a small entry way and utility room, then an upstairs living area and master bedroom and a downstairs living area with bedrooms) in mid-Michigan. The downstairs ...
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4 votes
1 answer
7k views

Where to connect c wire in furnace

I have 5 wires running to the thermostat from the furnace. The blue wire is not connected on either side. I'd like to connect it as my c wire for a smart thermostat. On the furnace I see W R Y G and ...
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8 votes
3 answers
4k views

Why are furnace/central AC blowers so inefficient?

I can buy a ceiling fan from Home Depot capable of moving 5,000 CFM of air for about $50, and it uses a mere 50-60 watts while doing it. By contrast, most furnaces seem to have blowers that operate in ...
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6 votes
3 answers
25k views

Do I need a rain\snow cover on this furnace vent?

Just bought a house that had a new furnace installed this summer. Vent number 1 in the image is for the furnace (2 is the water heater and 3 is sump). As you can see in the image, 2 and 3 both would ...
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  • 423
2 votes
5 answers
30k 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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2 votes
1 answer
43k views

Why is my gas furnace now continually just blowing out cold air?

I had my heat set to 70°F all day and my gas furnace was blowing out warm air. Then out of nowhere, it started blowing out cold air for the past 3 hours. I tried turning off the furnace and ...
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  • 21
2 votes
0 answers
107 views

How do I stop the ticking noise coming from my furnace duct? [duplicate]

I've had some HVAC people here to look at the ticking noise coming from our furnace duct. One of them installed a brace on the piece in question. This seemed to make the ticking less frequent, ...
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1 vote
7 answers
31k views

Which furnace thermostats support variable swing/deadband?

My home furnace is currently controlled by a programmable Honeywell thermostat, but it regularly thrashes the furnace by turning the furnace on for just ten or twenty seconds. It seems that the ...
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  • 225
6 votes
6 answers
15k views

How often should the air filter in the furnace be changed?

Does the period of change of this air filter have an affect on the longevity of the heating and a/c system? What is a good rule of thumb to require replacement?
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5 votes
4 answers
13k views

How do I prevent harmonic resonance hum in PVC vent of newly installed hot water heater?

I just had a new power vented water heater installed (HTProducts Phoenix Light Duty) in our crawlspace. The contractor that put it in used part of the existing 3" concentric vent from the furnace we ...
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  • 51
4 votes
7 answers
10k views

What should I do with old furnace filters? [closed]

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, ...
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4 votes
2 answers
129 views

What are my options for heating an energy efficient home with low heating needs?

I have a super insulated, envelope home. I have R-88 in the ceiling and R-44 in the walls. Living in Northern WI I do have heating requirements, but nowhere near the output of the 90,000 BTU furnace ...
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4 votes
2 answers
217 views

How do you calculate the right size furnace to maximize efficiency?

Given that sizing of the equipment is the most important issue to get right to maximize efficiency, what are the factors an installer should take into account to determine the correct size? Is it ...
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4 votes
2 answers
5k views

How bad is it to attach a gas water heater to a gas furnace electrical circuit?

I'm looking to replace my existing water heater with a more efficient model. One of the things that makes better models more efficient is the replacement of the thermocouple / pilot control system ...
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4 votes
2 answers
24k views

Why won't my furnace turn off?

My furnace is running OK and heating the house. The problem is that I have the thermostat set to 66°F and it does not turn off when it reaches that temperature. I can turn it off manually at the ...
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3 votes
1 answer
142 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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  • 185
3 votes
1 answer
848 views

How well would a hydronic furnace work with a gas tankless water heater?

My current heating system (in Ontario) is an oil hot water tank in a closed loop with a hydronic forced-air furnace (Enerzone XAH 68). The water circulates through what is basically a heat exchanger ...
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  • 259
3 votes
1 answer
1k views

Timer for house ventilation switch - high/low voltage wiring

I have a home ventilation switch that I would like to wire a timer to. This switch is located in my upstairs hallway, and when flipped it turns on the furnace fan blower and the main bathroom exhaust ...
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3 votes
2 answers
5k 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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2 votes
1 answer
14k views

Ecobee3 not turning on heat, but fan is on

I have an Ecobee3 that has been successfully working (both heat, fan, and AC) for the past 6 months. Recently I was trying to get my humidifier working so I was playing around with some wires, which ...
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2 votes
1 answer
657 views

Connected C-Wire (previously unused) to thermostat, but still no power?

In search of help with hooking up a Nest Thermostat E. I have seen several threads seeking solutions for similar issues and have troubleshooted with their proposed solutions with no luck. I am ...
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  • 21
2 votes
3 answers
36k views

Furnace runs for about 5-minutes only and shuts off

Furnace (Lennox G40UH, 12 years old) runs for about 5-minutes (sometimes as high as 7-minutes) and they turns off despite the heating call from the thermostat continuing. Flame sensor has been ...
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2 votes
2 answers
725 views

Tempstar (ICP) furnace short cycle (runs 10 -15 minutes) then repeats

I have a tempstar (ICP) furnace put in when the house builder built the house. Model is N9MPD075F12A2. Installed late 2009. This problem only happens with the furnace not the AC. When calling for ...
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  • 51
2 votes
1 answer
4k views

No power coming from c terminal on furnace

I am trying to set up a nest. My system was a simple heat only R/W wire set up. I attached the green wire to the c terminal on my furnace, but no power is being fed from it, or at least the Nest is ...
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  • 297
2 votes
2 answers
338 views

Adding a C Wire using a 24V AC Transformer to a 2 Wire Heating System for Nest

Continuation from Can I use any of my existing oil control terminals (TTFFAA) for a C wire? EDIT: Wanted to finally say this is SOLVED with help from @JPhi1618 (see conversation below). If you have a ...
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  • 33
2 votes
2 answers
10k views

Is it safe to replace a Furnace pressure switch with a different one?

So I had some problem with my gas furnace and a technician came by to install a new one but it doesn't have the same rating and only has one tube instead of two. He assures me it's fine but I thought ...
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2 votes
1 answer
648 views

Low voltage over C wire at thermostat

Similarly to this question of the same name, I am reading low voltage over the R,C wires at the thermostat. Unlike that question, however, the voltage is unusably low. I am only reading 2V over R,C ...
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  • 153
2 votes
1 answer
13k views

Why won't my Heil 7000 natural gas furnace ignite?

I have a Heil 7000 gas furnace Model: NUGK100DH12 Serial: L933050100 When we turn it on at the thermostat, the exhaust blower will kick on. We checked to be sure the gas is reaching the unit and ...
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2 votes
5 answers
36k 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 ...
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  • 128k
2 votes
1 answer
504 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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  • 2,869
1 vote
3 answers
1k views

Will a high efficiency furnace vent etch the brick on my house?

My neighbour just informed me that they had to change the vent on their high efficiency furnace. The furnace vents between our two houses and it used to have an elbow on it directing it along the ...
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1 vote
4 answers
46k 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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