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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3k 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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3answers
12k views

Why does the gas furnace blow cold air at the start of the heating cycle?

What does this problem sound like? There is a 25 year old gas furnace in the house we rent. (The guy that owns the place claims there is NO problem at all. He said the igniter is brand new and ...
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2answers
1k views

How is a high altitude natural gas burner different?

What is the difference between high altitude natural gas burner and conventional low altitude gas burner and why high altitude natural gas burner are needed?
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1answer
83 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
283 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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2answers
750 views

What is this name of this vent attachment next to my furnace?

What is the name of this silver vent attachment thing at the bottom of the picture? It is attached to the side of our gas furnace. The black part is an insulated air duct which goes to a vent ...
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1answer
90 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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3answers
6k 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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1answer
27k views

Why is water collecting in the base of my furnace?

I changed my filter the other day and noticed a pool of water in the bottom of the furnace, below the filter. The humidifier has been off so that's not the issue. I removed the furnace panels and see ...
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2answers
3k views

How do I troubleshoot an electric furnace?

I have a Coleman 3300-9051 electric furnace w/AC. The blower continually runs. Where do I find a repair manual and/or what could be the problem. How do I test it.
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2answers
7k views

What would cause a furnace to shut off prematurely?

I've got a Carrier Weathermaker 8000 furnace that shuts off about 90 seconds or so after ignition, started doing this recently. I get flashing code "33" which indicates: The code indicates: 33 ...
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3answers
22k 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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2answers
354 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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3answers
248 views

Can a furnace with a variable speed blower be used in a multistory house?

I just had an HVAC guy out to give me an estimate on a new Carrier Infinity series furnace and he said the second floor rooms will always be colder because the thermostat is on the first floor and not ...
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1answer
274 views

Should I use a quick or gradual 90 in my flexible A/C ductwork?

To elaborate a bit more. If you are running an 8" duct off the supply, would you do a quick 90 degree towards the destination or do a gradual 90 degree? I would guess a quick would be better because ...
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1answer
1k views

How can I prevent water from entering through water heater/furnace exhaust vent?

I have an exhaust vent in my basement (Amerivent Type B) which takes the exhaust from my gas furnace and water heater goes out the basement wall, and up my chimney. A little bit water is coming in to ...
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1answer
578 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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4answers
7k views

Why would a furnace overheat with a standard density filter?

Some time ago I found my furnace (gas, forced air, downdraft) was getting stuck on, blowing cold air. I could reset it, but it would happen again after a while. After calling out a service man, I ...
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2answers
539 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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1answer
99 views

Can I replace my draft inducer blower with a model of a slightly different speed?

My furnaces draft inducer blower sounds like a snow blower running, so I set out to replace it. Finding a replacement part proved difficult, but I found a site advertising a compatible part and ...
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1answer
357 views

Is it normal for air to be leaking from where the drain hose connects to the central A/C unit?

I'm trying to determine if I have a leak around my central AC unit. Basically when the unit is on, I feel cool air blowing outside the "furnace plenum" as I believe its called. If you look at this ...
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1answer
207 views

Where can I find resources on Gas Furnace manufacturers

We are going to replace a 30 year old residential gas furnace. We have estimates for furnaces from Rheem, Trane and Bryant. This is a rental, so we aren't going for the 95% with tax rebate but ...
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1answer
103 views

Why does my gas furnace run once then wont come back on until reset when temps are below 30 outside?

THE PROBLEM: My gas furnace will run one cycle and then not come back on until the switch is reset. Once the switch is reset it will kick on immediately run once and again I will have to reset before ...
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3answers
8k views

Does a whole house humidifier go on the intake or outlet of the furnace?

On what side of the furnace do I install the tank of the humidifier (the warm side or the return air side)?
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5answers
65k 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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2answers
845 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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1answer
52 views

furnace question

I have a tenant that constantly sets the thermostat at 90 degrees for the heat. I have told her several times to stop because she will burn the unit up. What are the consequences of this and how long ...
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1answer
10k views

Which way does the air flow through my furnace?

Below is my furnace and I need to change the filter however I am unsure which way is the airflow direction. Red or Blue?
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2answers
3k views

Furnace flashing 4 times (Ducane)

My Ducane furnace flashes 4 times, runs for 5 minutes, and then the burner goes off. When the limit switch is jumped it runs good. What needs to be changed here?
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1answer
7k views

Why does my pilot light go out when I release the pilot light knob?

My furnace pilot light will not stay lit. I can light it and depress the pilot switch for 2 minutes. But, once I let go of the button, the pilot immediately goes out. Does my thermocouple need ...
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2answers
2k views

Does it matter where my furnace condensate pump gets power from?

The existing condensate pump for my furnace recently died. It was hard-wired directly into the electrical panel of the furnace but I was able to disconnect it. However, when looking for a new pump, ...
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1answer
35 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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2answers
4k views

Should my furnace closet have this huge duct opening into the unconditioned vented attic?

So my interior furnace closet has a huge duct in it that connects the closet to the unconditioned vented attic right above it. Needless to say, this is a huge air leak into the conditioned part of the ...
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2answers
12k views

Is my furnace operating normally?

I just moved into my house and I am wondering if this is normal for a furnace. So I have my furnace set to 68 degrees. The temperature on the thermostat says 66 degrees. The furnace is on, but does ...
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1answer
22 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
171 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
137 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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2answers
2k 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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1answer
220 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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1answer
365 views

How do I determine/control which heat source is used (heat pump, oil)

I have a heat pump and an oil furnace for backup. How does the HVAC system know when to use the heat pump and when to use the oil furnace? Specifics: I have a Honeywell TH8320U1008 thermostat ...
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1answer
295 views

Is it a problem that I have two of each color wires on my Honeywell thermostat?

I am thinking about upgrading my Honeywell thermostat. Every thing I have seen describes / shows a single wire for each color. My current thermostat has two wires connected to each terminal (two green ...
2
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1answer
546 views

Can I properly install Roxul mineral wool batts in a mostly-drywalled stud bay by pushing them up from below?

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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2answers
460 views

What could be causing my gas furnace to make a loud noise?

I have a comfort air natural gas furnace when it call for heat,their is a loud boom noise,could the hot surface ignitor have a crack or needs replacing?
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2answers
584 views

How do I make my gas furnace throw out warmer air?

I just bought a new house. It has a 2007 gas furnace. The make is a 2007 heil furnace . I would like to know how to adjust the furnace to make it throw warmer air out of the ducts.
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2answers
3k views

Can I remove the fresh air supply that is attached next to my furnace?

It looks like my gas furnace is already vented but I'm not sure. There are two white pipes from the top of the furnace that are vented outside. The furnace is a Trane XR90. We have cold winter climate ...
2
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1answer
480 views

What is a quieter alternative to gas forced air heating?

My small 1BR apartment has an old gas furnace that works great, but costs my landlord too much to insure. He plans to install gas forced air, an in-unit upright furnace. I'd love to suggest a ...
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2answers
698 views

Can I move my furnace room ventilation intake closer to my furnace?

I live in a 3 story townhouse with a garage in the basement. Off the side of the garage is our furnace room. The ventilation and exhaust for the furnace goes to the roof. For ventilation (air coming ...
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1answer
6k 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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1answer
247 views

Is there a standard length on the PVC furnace pipes coming outside the exterior?

We have a high-efficiency furnace. Two pipes are coming outside the house as expected. However, right now, there is at least 2 feet or more of extra PVC on the exterior showing. Is there any ...
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1answer
585 views

Will I see any performance gains if I reconfigure my thermostat to control the second stage of my 2 stage furnace?

Our furnace is a two stage one that was installed last year (a Bryant 80t). When it was installed, it was installed with a thermostat for a one stage furnace. This appears to be because this model ...