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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No water pressure in heating circuit

I have a natural gas hot water furnace and I can't get heat. First I turn up the temperature at the thermostat and I hear the furnace turn on, the supply line gets hot and half way down the line it ...
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2answers
57 views

Furnace keeps kicking off and on

My furnace runs for a few min then flickers and shuts off and then the system recycles and it fires back up and the process repeats over and over and over etc....
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145 views

Very old, Coleman, through the wall (double sided) mounted gas heater not working

My home was built in 1957, I had a new heat pump system put in (which I now hate) 7 years ago. It works fine in the summer, but in winter it doesn't heat the house very well. At the time, I kept the ...
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2answers
35 views

Furnace fan runs all the time

our furnace fan runs all the time It doesn't switch off when the furnace does and keeps blowing cool air I've replaced the filter and it's still running The thermostat (RTH6400D) isn't set up to ...
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5answers
165 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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1answer
48 views

Can I replace the permanent filter in my furnace?

In my furnace (ruud ubhc-17j14sfa), there is a permanent, washable filter. It was there when we moved in 2 years ago. The house is about 10 years old now. The filter is pretty simple, more like a ...
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1answer
52 views

Pilot lights, but main burners don't on furnace with no flame sensor

I have a Rheem furnace in my house. It recently stopped working. It is the type where the pilot is not always on. Anyways, the ignition will kick in, and the pilot lights just fine. However, the ...
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2answers
69 views

Are my heat pumps using the right amount of power?

I'm trying to figure out if our two heat pumps are being power hogs and if there is something to do about it, or if they're operating normally. We bought our home recently and haven't been in it but a ...
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1answer
81 views

HVAC Contractor Didn't Install Drip Pan

I recently got the A/C unit and furnace in my basement replaced. When the company came out to do the quote, they stated that they thought I should have a drip pan, and the proposal that they gave me ...
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0answers
59 views

Can a furnace safety limit switch with manual reset be changed out with an auto reset switch?

I have a Ruud natural gas furnace from 1987. Overall it works well. I've had my home warranty service send out an HVAC tech a couple times for the high limit switch needing to be reset. It's a manual ...
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0answers
72 views

Is the Thermostat controlling the wrong zone? (Multi-zone heating with gas furnace)

UPDATE 12-29-2015: I've poked around and found, what I believe is, the board controlling the zones (Trol-A-Temp Mini-zone). Before I make any changes there, I chose to replace the thermostat on the ...
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1answer
82 views

How to wire a C-wire from a humidifier to a Carrier furnace?

I need guidance on a wire. One wire connects the humidistat to HUM. Another wire should go from the humidifier to COM24Vac. My COM is taken as you see in the picture. Is it an issue to wire the second ...
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1answer
1k 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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2answers
66 views

Can I retrofit a 2-speed or variable speed blower on a Payne PG8UAA forced air furnace?

My furnace blower is rather loud and runs at one speed. I wish to have the blower run at a slower speed to mix the air in the house when the heat is not called for. I see some furnaces have ...
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0answers
37 views

Oil furnace fan timing, limit temp setting

I just installed a new Crown oil furnace and a two wire thermostat. The furnace fires up fine but the blower won't turn on until it shuts down and the high temp limit control takes over. Then the ...
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2answers
75 views

wiring in a electric furnace to electrical subpanel

I have a 30 amp double breaker in my main home panel feeding my detached garage 100amp sub panel. Can i run a electric furnace with a 90 amp breaker in the subpanel. Or is this setup all wrong
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2answers
100 views

Furnace fan works properly intermittently

My furnace fan sometimes stays on and runs continuously. I can stop it by flipping the breaker for the furnace on and off. It then stays off. When heat is called for, the fan comes on again and ...
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0answers
310 views

My furnace has a C - common wire but air conditioner uses it - how to hook up smart thermostat?

I bought an ecobee3 smart thermostat which requires the C wire. At my furnace there is no circuit board but there was a diagram and I was able to locate the C - common wire, but it seems to be used ...
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1answer
167 views

hooking up a humidifier on a carrier infinity furnace

Hello I would like to hook up my desert spring rotary disc humidifier to my new carrier infinity model #59MN7 furnace. I see the control board in the furnace has a HUM (humidifier) terminal and a ...
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0answers
48 views

new furnace hurts eardrums

I just got a new furnace in my 800 sq. ft apartment. Single stage 80% efficiency 40K BTU Coleman. It seems much louder than my old one. The burners and the blower. And when I walk past the (single) ...
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1answer
111 views

Furnace: are flames in between the tubes bad?

In a Carrier Weathermaker 8000 gas furnace, is it normal for some of the flames to be coming out of the spacers in between the tubes? It seems like they shouldn't be there, since they aren't going ...
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1answer
60 views

Actual efficiency of an old oil furnace?

We purchased a house with what appeared to be a relatively well-maintained oil furnace, about 30 years old (installed in 1984). We don't have any records of annual oil usage, or any way to find that ...
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1answer
44 views

question about a gas furnace having to light repeatedly

I am new to this forum, but I will do my best to answer any questions I can (I am a general contractor with a background in engineering and residential construction and machine design) so, here is my ...
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43 views

Furnace on the Fritz - Any help greatly appreciated

I have a Tran XL90 - Model #: TUX100R948W6 It does not turn on in the "Auto" position on the thermostat. The fan does come on in the "On" position. However, it doesn't blow hot air. It has 3 ...
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23 views

miller mobile home furnace

When I press the reset button my furnace turns on and goes what seems to be a complete cycle. At this time the heat comes from the register nice and strong. When it comes on the second time it shuts ...
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5answers
2k views

Low voltage fuse blowing in furnace

I have an outside A/C compressor and indoor furnace fan combo in the attic. The unit was off and the 3 amp fuse was blown. I replaced the fuse and used the thermostat to turn the fan on followed by ...
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1answer
41 views

0v at DC thermostat terminal in furnace

I have an old (mid 80s) Rheem gas furnace I hope will last me through at least one more California winter. It's been known to go down into the upper fifties, so it has its work cut out for it. In any ...
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1answer
62 views

Furnace Fuse Blows Immediately

This afternoon, our Ruud furnace suddenly stopped working. After poking around a bit, I realized that the 3A fuse on the control board had blown. I ran to the hardware store and replaced it, but no ...
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0answers
7 views

Can I use any C terminal on a furnace to supply power to a thermostat? [duplicate]

I have a dual heat system with a gas and electric plenum. trying to install a wifi thermostat and found that the C wire on the furnace is connected but once it goes up and through the electric plenum ...
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0answers
231 views

No C wire terminal on my electric plenum but there is on my furnace. How do I solve?

I had a brand new furnace installed recently but also now picked up a wifi thermostat. The problem I now encountered while installing the thermostat is that my system also has an electric plenum as ...
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0answers
60 views

wiring for rheem 2 stage furnace

I am trying to wire a Honeywell 2 stage thermostat to a Rheem classic 90 gas furnace. At the furnace there is a white wire with a red strand connected to the R post, a blue to the C, green to G, ...
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2answers
172 views

Rain water leaking around attic furnace

I bought a house a few months ago and when I bought it I noticed what appeared to be a water spot on the ceiling of the top floor. Of course I didn't do anything about it until heavy rains over the ...
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1answer
131 views

How does old wood furnace work?

My mother in law has an old wood furnace in her workshop. It obviously is different than the typical wood stove you see. Does anyone have one of these? Or can anyone explain the theory behind its ...
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1answer
624 views

Correct Wiring for Furnace Blower Motor

After getting my furnace blower motor replaced, it now runs only in the following scenarios: 1. Mode "Cool" Fan "Auto" 2. Mode "Cool" Fan "On" 3. Mode "Heat" Fan "On" In other words it will not run ...
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70 views

Need help with a Trane XR90 gas furnace not heating

Diagnostic blinking light is 3. Tried calling Trane with no returned call and its getting really cold tonight. 30 degrees. Help plese
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2answers
2k views

Hvac Fan only blows in 'fan on' mode while heating

Our HVAC Fan only blows in 'fan on' mode while heating. In other words the fan will not blow in heat mode if switched to "fan auto". Both fan on and fan auto modes work when cooling. See image below, ...
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2answers
69 views

Replace or wash this furnace filter?

My mom's furnace has ductwork until right next to the furnace, where the return air instead goes into an obsolete electronic air cleaner that is basically as big as the furnace itself. The issue is ...
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1answer
76 views

Cant I just use a 24v wall instead of a tranformer?

I can just use a 24v wall transformer that I have plugged into my sprinkler system and use that in place of the transformer on my electric Central coleman furnace right? I would connect the hot line ...
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1answer
252 views

What is the optimal duty cycle for a furnace?

A heat load calculation of my home says it requires ~36K BTU/hr of heat at a normal winter temperature (40°F), and ~52K BTU/hr at the design temperature (24°F). An HVAC contractor has proposed ...
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1answer
45 views

How do I switch the furnace to heat mode?

I have an older good Sears furnace. It was on cool mode this summer and the fan could come on. I can't find how to switch it back to heat mode! Thanks. Linda
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1answer
536 views

What does this device on my new furnace do?

Can someone please tell me what this is? I had a 35-year old oil furnace replaced recently and the new furnace is obviously more complex and has many safety features the old one didn't. I've looked it ...
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1answer
60 views

How do I compare furnace models?

I need a new furnace, and I have quotes from two companies, for three different brands of furnace, Carrier, Trane, and Lennox. Both companies have provided the model numbers of the units they would ...
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1answer
101 views

New Thermostat installed but compressor comes on immediately

I have a new Insteon Thermostat that I'm using to replace my prior Honeywell t-stat. This is installed to a relatively new HVAC system (both AC and Heat) that DOES have a "c" wire. I've attached the ...
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0answers
142 views

What makes a furnace pilot valve whistle?

I have a furnace that started whistling, recently. I have read that gas pressure changes can cause this. Others have remarked how seasonal gas changes can lead to a properly-adjusted furnace to ...
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2answers
253 views

My goodman furnace is not igniting my burners

I have a goodman furnace and when it is calling for heat the ignitor comes on and goes off and comes on again and the burners never comes on what could be the problem
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1answer
25 views

Central Furnace blower alwas on, even with thermostat disconected

A technician told me it was the electronic control board that has the blower relays on it , I replaced it and still has the problem, I've been reading here online about a limit switch for the blower ...
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1answer
84 views

Thermopride OL5-85 oil furnace no longer works

We bought this old house where the oil furnace worked for a while. Now it does not work even after adding enough oil and priming the furnace. We have already pushed the reset button..so I do not dare ...
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1answer
272 views

Furnace reaches temp, shuts off but wont come back on

I have an American Standard furnace (natural gas)with a manufacture date of 2004. The thing won't come on unless I power it off (have a switch right beside it that serves this purpose), let the fan ...
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1answer
36 views

What is required for seasonal maintenace of a heat pump?

Over the years I've had several local HVAC companies provide seasonal maintenance of the heat pumps and propane furnace in my house. It seems that every technician--even within the same company--does ...
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1answer
70 views

How can I improve the directional flow of my furnace exhaust pipe?

This one's for the creative folks. I'm in a condo on the top floor and I have a side neighbor. Both our furnaces exhaust out the back, under a four-foot roof section overhang (sticks out about a foot ...