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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2answers
177 views

Do cold air return vents also supply combustion air?

I’m wondering if the cold air return vents located inside certain rooms of the house are also the intakes for furnace combustion air. In other words, are those the vents that feed fresh air into the ...
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2answers
960 views

What should the plenum temperature be on a modern furnace

I had a tech out to review my furnace that's not keeping up - a Trane XV80. They poked around, and saw that the plenum temperature is 95F. They then told me that it should be around 140F, which is ...
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1answer
413 views

Flame sensor in Trane XV90

I have Trane XV90 that was blowing cold air while it was on heat. I have recently changed the ignitor (which seems to work just fine) and the flame sensor (which seems to be failing already). I just ...
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3answers
7k 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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1answer
409 views

Not able to find Lennox ML193UH furnace filter

I have a Lennox Merit series gas furnace ML193UH in my attic. The furnace turns on, but no air blows out of it. So i figured the filter needs to be changed. But I'm not able to find it. The pictures ...
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35 views

What can cause a furnace to work worse

I have a 10 y/o trane xv80. It’s -3F in Chicago, and the furnace is struggling to keep 64F in the house, while set for 72. I don’t remember it being this bad in years past. I had the furnace taken ...
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1answer
56 views

Fuel oil burner running intermittently

Fuel oil (Beckett oil burner) here. It's -20°F outside right now and the house is at 61°F even though I have the thermostat cranked up to 75°F (we have a thermometer in the house as well, ...
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780 views

Need Help on Adding a Common Wire for Nest

I recently purchased a Nest thermostat. After couple weeks of usage, the Nest is constantly shut down due to low battery. I search online that adding a common wire is the go solution for this. However,...
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385 views

Hot surface ignitor does not glow occasionally

Can one of you experts please help with this unusual issue? The hot surface ignitor does not go on occasionally. So far, I had this issue 3 time in the past week. My furnace: York gas furnace with ...
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0answers
547 views

Goodman furnace starts after turning on / off 7 times

I have a Goodman furnace from 2000 has been running great until recently it does not seem to cinc with thermostat. when you shut unit down and turn back on it will go through all motions of starting ...
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2answers
230 views

Why would furnace not come on immediately?

I had a brief scare just now. It is 7-degrees right now and getting colder so I definitely don't want a furnace failure. I came home and house was at 62 with thermostat at 64 (my standard not-at-home ...
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1answer
180 views

Ecobee3 Setup and furnace only has W G R

My existing thermostat has 4 wires (missing C) so I'm attempting to use the Power Extender Kit (PEK) at the furnace control board. Only problem is, I only have 3 wires that are obviously labelled at ...
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1answer
63 views

Does anything look wrong with this Furnace burner start up?

Here is the back story: Starting to finish basement, needed to exhaust my furnace outside instead of drawing in air for combustion inside the house. Hired HVAC person to do this in the fall. Winter ...
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3answers
543 views

Why is the furnace heating the house far past the thermostat setting

Problem: Furnace came on as usual in the morning but failed to shut off after the set temp on the thermostat was reached. The house temp (as measured on the thermostat) reached about 10 degrees higher ...
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2answers
693 views

Furnace entering lockout mode - air flow problem?

I have a Nordyne KG7SA, about 2009 vintage, which has begun acting strangely. We started noticing that the thermostat would drop several degrees below the set temperature before engaging. More ...
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2answers
2k views

Can I add four new ducts to my HVAC trunk line?

I am finishing my basement and need some insight from someone who understand HVAC design. I would like to know if my main trunk line (the 34' one in the diagram) can handle another four 6" ducts off ...
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2answers
1k views

Can I use the Y wire in place of the C wire for my new thermostat?

I'm looking to wire a Honeywell Lyric T5 to my furnace (I do not have an air conditioner, I do have a humidistat). My current wiring at the thermostat is G,W,Y,R. At the furnace it's G,R,C, and 2 at W,...
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1answer
59 views

Rapid on/off cycling of furnace

My 50-year old wall furnace keeps cycling on and off as it gets near the set temperature. Can I fix this by changing to a new thermostat? It's a 2-conductor cable (no blower).
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1answer
293 views

Resonance in pipes, heating system

I have resonance in the heating system pipes. Touching the pipes near the boiler (natural gas) pump I can feel ever so slight vibration, most detectable by touching the pump motor. Background: About ...
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1answer
312 views

Armstrong S-25 Pump Motor Lubrication?

Recently replaced a leaking bearing assembly on my Armstrong S-25 pump. The previous one required oiling, the new one is the permanently lubricated MF/BF model. I look forward to not having to ...
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1answer
2k views

Thermostat won't always start heater on its own

I have a gas furnace that seems to work fine; it keeps the house warm when things are running as expected. Sometimes, however, we'll notice the house is getting cold. The temperature on the ...
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1answer
4k views

HELP!! Why is my stove turning my lights and furnace back on when they go out?

For the last few days whenever I have more than one or three lights on they go out(includes the furnace) and the only thing that turns them back on is my stove. What is this?!?!
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17 views

Furnace motor not kicking on

I have a goodman furnace who's fan motor will keep running. it's like it is trying to kick on, but it can't will run fast then slow down then fast again. the only way it will kick on is to turn ...
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3answers
1k views

Need info on AFCI requirements

Are AFCI breakers required on 30 amp dryer circuits and 50 amp furnace and stove circuits or just the 20 and 15's? I haven't done residential in a long time. Thanks fellas.
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42 views

furnace wont kick in

My furnace seems to work intermittently. overnight its seems to stop... i have checked the thermostat and it shows says it is heating. fan is on auto, but nothing coming out. when i turn heat to off, ...
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1answer
1k views

Blower motor turns on before furnace heats up all the way

I have a Honeywell furnace and when it starts the exhaust fan kicks on then the flame starts (it's a propane furnace) it warms up between 30 seconds to a minute then the main blower kicks on but it ...
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2k views

Goodman gas furnace won't light

I am trying to resurrect a Goodman gas furnace that hasn't run in a few years. I have gas to the unit, but no ignition. Vent blower starts up initially, but soon goes to intermittent operation, I ...
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1answer
194 views

Where to connect c wire

I’m installing a new WiFi thermostat that needs the c wire. I ended up running new thermostat wires that contained the common wire but now I’m stuck on where to connect it to the furnace. Can ...
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1answer
7k 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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1answer
464 views

C Wire for Thermostat

I am upgrading my thermostat (Have AC & Heat) and found that it doesn't have the "C" wire that I need to power my new thermostat. The furnace does have a terminal for C, but only condensation pump ...
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1answer
776 views

Aprilaire 56 Humidistat not getting power

I have an Aprialaire 56 humidistat that is connected to an Aprialaire 560 humidifier. Currently the humidifier is not turning on and after testing the wiring with a multimeter, the wires going in to ...
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1answer
1k views

Separate furnace & a/c units on same breaker

Long story short: with both units on one breaker, each one is kicking on one after the other to try to reach one temperature. I have turned the a/c disconnect at the outside box, and the a/c is still ...
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1answer
2k views

Blower fan works w/ a/c “auto”, not with heat “auto”

I know there are similar questions out there but are there any new ideas? When I turn on my heater, the gas fires up but the fan doesn't turn on. I know the fan is still working because it will turn ...
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3answers
3k views

How do i hook up a new 5 wire cable to an existing 4 wire furnace

I would like to replace the existing thermostat wires on my 2000's era janitorial furnace with the upgraded 5 wire setup that will allow fan control of my Honeywell wifi 9000 thermostat. I was going ...
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127 views

how to deal with oversized furnace

I recently got a new furnace for our 1200 sqft house in Denver CO. We are planning on adding a second story in a year and I was going to wait until we did that to replace the furnace. Then the furnace ...
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1answer
2k views

How to use a gas fireplace and a furnace together?

So here's my setup: Living room has both a thermostat for the gas fireplace (dumb on/off thermostat) and a thermostat for the whole house (smart/Nest thermostat) on the wall together. Living room has ...
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1answer
349 views

Help with smart thermostat wiring

Installing an ecobee4 thermostat. Have a 2 stage furnace with ac. Had a Trane furnace installed couple years ago and just noticed it's jumpered between W1-W2. Old thermostat wire was only 4, ...
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4answers
1k views

Rust and ash in my AC/furnace - should I be concerned?

TL;DR - Furnace/AC generates a lot of rust flakes and ash, not sure what this means. UPDATE - An inspector came by to look at the furnace. While the inspector didn't find anything broken, he said it ...
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2answers
207 views

Need to wire “C” wire to thermostat

This is my furnace board. I don't see anything with a C terminal. Are there any connections on this board that I can use as a "C" terminal? Below is the thermostat I'm trying to hook up. This is how ...
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1answer
49 views

Furnace stop and start continuesly

I notice today that my new furnace will stop after about half hour and start again in a few minutes. The room temperature is 66 and I set it to 70. It took several stop and start before it reaches 70. ...
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1answer
31 views

Lennox HE propane furnace

I have a Lennox HE propane furnace in the cottage that is set to 41 degrees when we are not there. We head up most weekends and when we get their I boost the temp to 65 deg and get a fire going in the ...
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0answers
152 views

Inside HVAC furnace, zero ohm between R wire and W wire, is that normal?

I have a Lennox system (G27M series). The transformer has a 3amp breaker. It trips time when the R wire and W wire are connected (heat is on). To find out where the circuit is short, I attempted to ...
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2answers
225 views

Furnace Defective Vacuum Switch

The furnace in my house is having a problem. The furnace overall works well and heats the house fine. The problem is that it cannot turn itself on. There is a Nordyne vacuum switch on it that is ...
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2answers
426 views

B-Vent Flue Condensation

We have had a water spot appear and not go away in our master bath. After looking around I found out that the flue pipe, B-Vent, is dripping with condensation when the furnace is running. I have ...
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2answers
912 views

Furnace keeps cycling on and off until it's up to set Temp

I have a Philco 80,000 btu two stage with variable speed blower, high efficiency furnace with a two wire thermostat, on/off. The furnace 6.5 years old and when the thermostat calls for heat the ...
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3answers
621 views

How do I connect a Class B vent to this heater

When I moved in a two years ago this heater wasn't working. Turns out the tree roots crushed the gas line. When I did my patio I had a new gas line put in. The heater fires up and runs good. The prior ...
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1answer
692 views

Gas Furnace blowing hot air into room, flue is cold

We have a 2-year old gas furnace connected to water pipes and radiators throughout the house. It just turned on for the first time this year and is blowing a large amount of very hot air directly into ...
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0answers
23 views

coleman gas heat only furnace,

When heat comes on, furnace runs for about 8 mins then cycles off. When the heat clicks off I get a switch open code from the board. While the furnace is running I get a normal operation code. As soon ...
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1answer
2k views

Where is the pilot light on my Carrier Infinity Series 48XT dual fuel hybrid furnace/Air Conditioner?

THE ISSUE We bought a new home and it came with this state-of-art system. The model number is #48XT-A6011530TP. Haven't had much luck finding information about this model or type of unit online. I'...
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2answers
71 views

Furnace third burner won't come on

I have a Trane furnace and the third out of three burners doesn't want to come on. The surface ignitor will light, the gas to the first two burners kicks on, but the third burner that that shoots ...