Warm air furnace installation, troubleshooting, repair FAQs:

Questions & answers about how to repair a home heating furnace - force warm air heat troubleshooting.

This article series answers just about any question about forced air or warm air furnace central heating system troubleshooting, inspection, diagnosis, and repairs in residential buildings and homes. Sketch at page top courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

Warm Air Furnace Troubleshooting or Inspection FAQs

These questions and answers about warm air heating system furnaces were posted originally at FURNACES, HEATING - home. That's a great place to start reading if you're having trouble with your furnace.

If you have no heat a all and your heat is by forced or gravity warm air, see HEATING LOSS DIAGNOSIS-FURNACES.

If you don't know what kind of heat your building uses, we explain how to figure out the answer in more detail

at HEATING SYSTEM TYPES.

On 2019-01-14 by (mod) - how to find out the age of your furnace

Todd to find out how old your furnace is,

Check the furnace brand and model, find the data tag, and if there is no manufacture date on the data tag, find the serial number on the data tag.

The manufacture date is usually encoded in the furnace serial number.

But exactly how the manufacture date is encoded in the furnace serial number is at least brand-dependent.

For that reason, once you know at least your furnace brand (manufacturer) and have found its serial number, you can look up the furnace age decoding guide for your particular heater

at AGE of HEATERS, BOILERS, FURNACES

where we give several documents that decode those serial numbers.

In that article we also give links to Furnace and Boiler manuals, age decoders, and contact information sorted alphabetically by manufacturer.

For example suppose your furnace is made by American Standard

in the article I gave you'd find this link

MANUALS & PARTS GUIDES - HVAC Brands A-E - & Master Index to All Brand Names, HVAC manuals, wiring diagrams, installation and repair guides -

and at that page you'd scroll down through the alphabetically-organized list of manufacturers (or using your browser's search feature to search our page for AMERICAN STANDARD)

Until you find find this link:

AMERICAN STANDARD boilers & furnaces

and clicking on that link

you'd find all the information we have on that brand, including an

American Standard HVAC Data Tag Age Decoder

On 2019-01-14 by Todd Robinson

How do I find out how old my furnace is from the information inside with the

On 2018-03-07 by (mod) - if you smell burning at heating equipment

Shirley

Watch out: Any time you smell burning at heating equipment there is a risk that the system is unsafe - it should be left off and of course you'd call your heating company for emergency repair.

On 2018-03-07 by Shirley Nixon

I’m worried cause last night the heater ,fan and all just stopped, you could smell like burning something just before it stopped but I’m worried cause after all day and a few hours of last night it stopping working, it just made a air release like noise and the thermostat is completely turned off / it did this for maybe 30 seconds , but’s quiet now , could it be dangerous to us?

On 2018-01-02 by (mod) - knocking sound at furnace

Is the knocking sound is continuous, look for a loose blower or squirrel cage fan or fan bearing.

By the way a washing machine that's out of balance or has its feet set un evenly on the floor will wobble and make horrible knocking sounds.

On 2018-01-02 by L

Gas warm air furnace located in attic of townhouse. Entry is in 2nd floor laundry closet above washing machine connection

s. Temps are unusually cold at 23 Fahrenheit. Heat set on 71. When air is blowing I hear a knocking noise coming from laundry closet.

Thought perhaps water connections for washer but no change when I turned them off.

No other issues other than frequency of how often unit runs but assuming that is due to weather. It turns on every 15 minutes or so and stays on about 3-5 minutes.

On 2017-12-07 by Jon

My forced air heater works great then just stops & the safety button pops out. I start it again & it runs for a minute or 2 then stops again. I restart it usually 2 more times then it stays running. It runs for a day or 2 then does it again. I’ve bled it several times but it keeps happening. Maybe an air bubble still or the pickup is dirty? Help!

On 2017-12-04 by (mod) -

Gary, it's normal for the blower fan to continue to run for a short time after the furnace turns off. If your fan runs continuously without stopping you might want to start with the Diagnostics in this article

https://inspectapedia.com/aircond/HVAC_Blower_Fan.php

On 2017-12-03 by Gary

Forced air unit..sounds like the blower is still running after the heat goes off.?

On 2017-11-26 by (mod) -

You would know if the furnace turned on because you would hear the noise first of the burner even a quiet gas burner make some sound, and second when the heat exchanger warms up you would hear the blower fan turn on. If your furnace exhaust flue stays cold that's another clue that there is no flame fire nor anyone Singing Stars and Stripes Forever

On 2017-11-19 by todd

this will be a side wall of residence venter installation

consolidated industries mba100 nh5r quatro natural gas furnace and air-conditioning air handler.
has a draft inducer located inside the main access panel, and is oriented to discharge out the side of the unit.
this furnace located in the crawl space of the residence vents toward the base of the chimney, where it transitions to aluminum flexible dryer duct and enters the chimney into a cracked flue liner.

i would like to know if a power venter (i.e. field control type swg) installation is in addition to the furnace draft inducer or in lieu of the draft inducer.
the flue liner is cracked

On 2017-11-11 by Dina

Hi, I just moved into a home with a floor furnace. I believe it's a gravity furnace and I'm also thinking antique! So, I have the serial number, which is 29566, but I can't read who made it or the model number at all.

I can see the pilot light down inside but I'm wondering how do I know if the burner is functioning? I used the handy dandy key to make sure the burner is in the 'on' position, but now what? I don't know if it's supposed to remain quiet, hum, or flat out sing a few lines of America the Beautiful so I will know it's working.

Any advice at all, if even possible, would be awesome. Thanks!

On 2017-11-02 by james

we have an outside air conditioner which cools and runs through our clectric furnace system this summer everything worked fine then when weather changed and i switched the air off and went to the electric furnace and ran it for the day

I noticed a faint burn smell like hot wires but i took everything apart and vacumed the inside everything looked fine! do you need to replace the elements or what? this furnace might be about 1991 or so- I just bougth the house 2yrs ago but did not notice any smell last winter.

this is the first electric furnace I've had and not sure how they function?

On 2017-10-31 by Bev

My mother has cool air drifting lightly through the floor furnace vents when the furnace is not running. Is it normal to have this continuous air movement. The house is warm the floor is not cold but the air movement bothers her.

On 2017-09-22 by (mod) -

Dan,

If you are speaking about the place on the furnace itself to which the stovepipe, or what I call flue vent connector, actually connects to the heating Appliance, it might be called a color. But the part is going to be specific to the particular brand and model heater that you have.

If you tell me the brand and model I can help you find the parts explosion and we can use exactly the name that the manufacturer uses.

For example the part might actually be formed as the entire top of the Furnace itself or the furnace top cover.

On 2017-09-22 02:09:03.796767 by dan

need to replace part on hot air furnace where stove pipe connects. what is this called? flue box? breeching?

On 2017-09-17 01:19:21.175324 by (mod) - banging soun ds

Alice

If a heating equipment is making banging sounds it could be dangerous - you should indeed ask for it to be serviced.

Banging can be a flame or combustion problem; of course there could be other noise sources - such as some of the banging noises at

HVAC NOISE DIAGNOSIS

(that list includes both heating and cooling systems)

Let me know what you're told is found.

On 2017-09-16 04:21:51.196960 by Alice

Hi InspectApedia,

I've just moved into a place and the furnace downstairs sounds really sick. At some point in its cycle, it bangs repeatedly, like the sound a dryer or front loading washer if the drum has dropped and is scraping the chassis as it turns, banging on a rhythm- not good.

And at 11pm it's very loud. It does this several times over the evening, banging for approx 5-10 minutes each time at 15 minute intervals before suddenly falling silent. What does this indicate? Should I ask for it to be serviced?
Sleepy and grateful for your help,

Alice

On 2017-03-04 00:37:35.047955 by Anonymous

Thanks Tim I should have included that part in my suggestions - I was thinking of older gas fired appliances that don't use a solid state control module.

Your feedback will help other readers.

Usually a bad ignition controller will prevent the gas flame from igniting at all. That's not the same issue as a flame that ignites but then goes out.

On 2017-03-04 00:26:57.343751 by Tim - found a bad ignition controller

Just had that happen to ours last month...

in our case it was a bad ignition controller. Our furnace (circa 1980) has an intermittent pilot, meaning when you get a call for heat, it first turns on gas to the pilot and then ignites it with an electric spark, then once it senses the flame, turns on gas the main burners, which get ignited by the pilot.

Our old controller had failed so that as soon as the main gas valve came on, voltage would drop to zero, which would shut it off, then this would happen 6 or 8 times before the controller went into fail-safe mode and shut down.

On 2017-02-27 by (mod) - gas burner keeps going out after a few seconds

Check for a bad thermocouple or flame sensor

Check for CO or flue gas spillage at the draft hood

Check for inadequate combustion air

Watch out: these conditions are unsafe and risk fatal carbon monoxide poisoning

Check for a fuel delivery problem: blocked gas line, blocked pilot or burner orifices, spiders in the igniter, (really), lack of combustion air

On 2017-02-27 by Miguel

My gas furnace ignites but won't stay on for more than a few seconds before it goes out again. The induction fan and blower seem to be working fine.

The furnace just seems to go through a series of igniting then going out right away.

Sometimes, after a while it will stay on and heat to set temp and shut down appropriately, but then after the temp drops it will go back to a series of igniting then then flame out.

On 2017-02-27 by (mod) - gas furnace burner ignites but won't stay lit

Check for a bad thermocouple or flame sensor

Check for CO or flue gas spillage at the draft hood

On 2017-02-27 3 by Miguel

My gas furnace ignites but won't stay on for more than a few seconds before it goes out again. The induction fan and blower seem to be working fine. The furnace just seems to go through a series of igniting then going out right away. Sometimes, after a while it will stay on and heat to set temp and shut down appropriately, but then after the temp drops it will go back to a series of igniting then then flame out.

On 2017-02-18 by (mod)

Dave,

Please search InspectApedia for FURNACE RETURN AIR IMPROVEMENT to read some diagnostic and repair suggestions. It's pretty easy to make a lay-person's assessment of return air adequacy.

That's where I'd start. A more powerful fan isn't enough if the return ducts are inadequate, blocked, leaking, etc.

On 2017-02-18 by Dave

I'm told my very efficient, gas, forced hot air furnace is only operating at 50% because it lacks return air. I thought this furnace was more powerful and more efficient than the old one. I ran two cold air returns and one heat duct to the new large bedroom.

It doesn't do much. I was told to cut a large cold air return into my hardwood floor, in the hallway up stairs. I really don't want to do that. I have easy access in the finished basement dropped ceiling. will that work? Furnace is a Trane XL80 upflow / horizontal, gas-fired 2 stage, fan assisted combustion system the house is a ranch 24'x 60'. We heat 60% of the finished downstairs as well. Thanks for your consideration.

On 2017-01-11 by (mod)

Theo

I can only answer in theory as we have not a shred of information about your home. It is common for upper floors in homes to be warmer than we'd like and for lower floors to be cooler, if for no other reason than warm air rises by natural convection, passing upwards by stairways and even by smaller openings.

It would be very odd for that imbalance in heat to be caused by a thermostat as long as the thermostat is properly responding to calls for heat by turning the heating system on when temperature at the thermostat is below its setting and turning heat off when it senses that the call for heat has been met.

Sometimes a very simple winter-time step can improve the heat balance: closing upstairs room doors or even hanging a blanket or curtain across the top or bottom (better) of a stairwell can cut back the movement of downstairs heat up the stairwell.

On 2017-01-11 by theo

I have a two family home I had thermostat replace on bolt 1 st and the second floor and still the 2nd floor is too hot even when it shut the thermostat off

On 2016-09-26 by Sheila

I own a condo, 1,600 sq. ft. In a vintage 3 flat in Chicago. We have radiators and furnace serving all 3 units.

We are looking into individual heating units with central air in each unit. How long, would you estimate the work, how messy and how do we have heat during the installation.

Also rough estimate of cost for units, installation, labor?

On 2016-06-07

by (mod)

Do keep me posted - what you learn will help others, Chuck and stay safe.

Daniel

On 2016-06-07 by Chuck Milne

Good advice about the CM detector. I fitted three 18 months ago, in strategic places i.e. in the utility room the furnace is in, another outside the room, and yet another upstairs in the gallery bedroom.

The property is unusual in that it is a voluminous cavern of a living space (100'x 30'x 35' open plan) so my guess is the experts will take it at face value and throw away the standard rule book. I'll keep you posted.

On 2016-06-07 by (mod)

It makes sense to be careful where life safety questions are involved. I agree with bringing in a trained, experienced gas heat service technician. Your gas supplier should also be able to help.

Basically if a heater is installed in a small space it may lack enough air for the gas burner to completely consume it's fuel.

Complete combustion produces just CO2 (carbon dioxide) and water vapor.

Incomplete combustion Occurs if the gas burnerlacks enough oxygen (in air) so it then produces CO (dangerous Carbon monoxide)

An expert tests the exhaust for unsafe levels of CO using an instrument.

That could be due to improper chimney draft, bad burner adjustment, or insufficient combustion air.

In the last case one may add air from outside.

There are also simple rules of thumb about burner size in BTUs and room size that can suggest inadequate combustion air.

A pro can sort out the question for you.

Your immediate safety action must be to be sure your home has properly installed, located, tested Carbon Monxide detector alarms. If an alarm sounds, get everyone out right away and call emergency services.

Please keep me posted on what you are told.

On 2016-06-07 by Chuck Milne

Thanks again for your comments. I did study the link but couldn't determine a definitive answer. Unfortunately it's all getting a bit to technical for me as I'm not an engineer and I don't understand the jargon. Your efforts to help is much appreciated but I think the best way forward is to ask for a second opinion from another company. Kind Regards. Chuck

On 2016-06-03 by (mod)

Is your "engineer" actually a P.E. ?
Does the engineer actually have expertise in gas fired furnaces, chimneys, combustion air? P.E.s usually have something better and more profitable to do than servicing furnaces.
How did the engineer determine that the furnace lacked adequate combustion air.

Did you search InspectApedia for COMBUSTION AIR REQUIREMENTS to read details about estimating combustion air needs? It's true that gas fired equipment is **VERY** dangerous if there is inadequate combustion air as you'll produce high CO.

On 2016-06-03 by Chuck Milne

Hi. Sorry, yes my question was basic but just to start the conversation. The system is gas fired warm air and has venting going from the unit to a chimney on the roof. The unit is in a large utility room which has a good sized window which has an air vent.

The engineer has suggested I need to get a builder to punch a hole through the granite wall and install a vent. It has been in the building (Converted Church Hall) for up to 20 years but seems very efficient and we've experience 2 Aberdeen winters. I just thought it prudent to have it serviced but it seems to have opened a can of worms. Any comments would be appreciated

On 2016-06-02 by (mod)

Chuck It would be a bit of a stretch for me to pronounce legality having almost no information about your system, fuel, venting, etc. (and technically it's your local code inspector who declares it "legal" or not under building codes.

But certainly if the system is fossil fueled (oil or gas) its exhaust needs to connect to a working chimney and vent to outside.

Speculating and guessing all over the place since your question didn't give much information, if your engineer is referring to inadequate combustion air, that she thinks would be solved by providing outside air, that's a critical safety observation. Search InspectApedia for COMBUSTION AIR REQUIREMENTS to read details.

On 2016-06-02 by Chuck Milne

Hi. I have inherited a Johnson & Starley warm air heating system. I asked a local engineer to service it and he advised that it was illegal because there was not outside venting in the utility room it is housed in. Is he correct?

On 2016-02-21 by (mod)

If the thermostat is calling for heat and the furnace is not turning on, I suspect a loose wire or a bad control board. Intermittents are hard to find. Start by eliminating the thermostat and its wiring from the equation: connect the two thermostat wire terminals at the furnace (the same as the thermostat calling for heat). If the furnace runs OK the issue is in the TT or its wiring.

On 2016-02-21 by Roy

I have a gas furnace high efficient Bryant plus 90. It was not heating to the appropriate temperature and at times would not come on until I turned off the power at the furnace and turned it back on. I check the thermostat and cleaned the electronic filters. It worked correctly momentarily but now is back to not coming on at times until I reset it and then doesn't heat to the temperature setting. other times it cycles and works properly.

On 2016-02-04 by Amanda

Hi. Our hvac system is now making a buzzing sound when the heat comes on. A few days befor I noticed the emergency heat came on for no apparent reason. I am calling for technician, but wondered if anyone had any thoughts? Thank you.

On 2016-01-31 by (mod)

You are describing what may be a very dangerous condition. If the furnace heat exchanger is cracked, rusted, or has a hole in it then you may be venting dangerous flue gases including potentially fatal carbon monoxide into the occupied space. My suggestion is to ask for an inspection by a trained heating service company technician.

On 2016-01-31 by JaPete

My fiancee's house (manufactured) has forced hot air oil furnace. During times he's not there, the thermostat is set at 58. When returning home, the heat is turned up to 72. While the furnace is running, it smells like exhaust coming through the ductwork. The furnace was cleaned 4 months ago.

There is no basement in the home, only a crawlspace. This is where the oil tank is located. There is a woodstove set up in another room but is not using the same chimney.

What can be causing this problem?
The man who cleans the furnace doesn't find anything.

On 2016-01-15 by Real8@cox.net

Is the noted furnace 110 or 220 volt supplied

On 2016-01-09 by (mod)

check for fuel supply, then check for a bad thermocouple

On 2016-01-09 by neon

My conv. heating system will start but will not ignite and fire the gas burner?

On 2016-01-06 by (mod)

I would shut the system off and call for repair; it may be overheating.

On 2016-01-06 by (mod)

Re-posting:

AUTHOR:Darrell cotrell (no email)
COMMENT:Space heater,it's brand new is making a high pitched noise when burner comes on and I'm finding a white powdery substance on top of heater surface.

On 2016-01-06 by (mod)

Re-posting:

AUTHOR:Darrell cotrell (no email)
COMMENT:Space heater,it's brand new is making a high pitched noise when burner comes on and I'm finding a white powdery substance on top of heater surface.

On 2016-01-06 by (mod)

Re-posting:

AUTHOR:Darrell cotrell (no email)
COMMENT:Space heater,it's brand new is making a high pitched noise when burner comes on and I'm finding a white powdery substance on top of heater surface.

On 2016-01-06 by (mod)

Re-posting:

AUTHOR:Darrell cotrell (no email)
COMMENT:Space heater,it's brand new is making a high pitched noise when burner comes on and I'm finding a white powdery substance on top of heater surface.

On 2016-01-06 by (mod)

Re-posting:

AUTHOR:Darrell cotrell (no email)
COMMENT:Space heater,it's brand new is making a high pitched noise when burner comes on and I'm finding a white powdery substance on top of heater surface.

On 2016-01-06 by (mod)

Re-posting:

AUTHOR:Darrell cotrell (no email)
COMMENT:Space heater,it's brand new is making a high pitched noise when burner comes on and I'm finding a white powdery substance on top of heater surface.

On 2016-01-06 by (mod)

Anon: please search InspectApedia.com for HEAT EXCHANGER LEAK TEST to see details.

On 2015-10-28 by Anonymous

How to tell if the heat exchanger is gone

On 2015-10-17 by Anonymous

I cannot find where to replace the filter. I have a gas heater with forced air. It's not in the furnace.

Question: how to find the age of my Lennox GN1-105C Gas Furnace

(Nov 23, 2011) jack said:
I am trying to find the age of my Lennox model GN1-105C gas, gravity fed air, furnace which the only thing I have had to do to it in the last 40 years besides cleaning is change the thermo-couple.

Reply:

Jack, in the ARTICLE INDEX near the end of this page where you see our links to heating-related articles and at the ARTICLE INDEX found at CONTINUE READING just above I have added
AGE of HEATERS, BOILERS, FURNACES
please take a look at that article and if questions remain just ask and I'll do my best to assist further.

Question: why won't my furnace heat the house to the thermostat set temperature

(Jan 4, 2012) patrick said:
My furnace will not reach the set temperature (winter now). I'd set it to 22c, the room temp starts at 17c, the furnace comes on, but can never hit 22c before it turns off again. I have no leakages. What could be the possible reasons?

Reply:

Check the building for unusual heat loss points;

Check the furnace BTUh rating against the building size and rough estimate of heat loss

Check the furnace for overheating in the heat exchanger by watching the fan limit switch dial to see if it's cutting off at high temperature

Question: musty odor from heating registers

(Jan 17, 2012) Musty smell said:
I have musty smell coming from registers. Furnace is on concrete in basement, but basement is dirt floors and dirt wall. Any ideas how to fix this. I was told when they put it in the basement that the basement smell would not be smelled through duct work. Otherwise, I would have put furnace in garage.

Reply:

Musty, there is not enough information in your note to reliably diagnose and cure your musty smell complaint, but I can suggest some places to start investigating:

1. leaks into the return duct from unconditioned spaces such as dirt floor and wall basement

2. improper return air source register location picking up air and odors from #1

3. water or moisture sources in the duct system or air handler contributing to mold growth

4. a mold reservoir in the building that has not been found, telegraphed via the HVAC system

Question: furnace motor runs for no reason

(May 7, 2012) MB said:
My furnace "motor" runs on its own and for seemingly no reason. For example the temp in the house today is 67 and the thermostat is set at 58. The motor will run for hours with out the burner or blower turning on. To clarify; I only have heat and not ac.

Reply:

Check for shorting wires controlling the furnace or fan or thermostat

Question: can a heat exchanger be cracked

(Nov 10, 2012) Eddie C said:
My furnace its going on and off. The repair man upon inspetion said: the heat exchange it's cracked and need to be replaced. Is that possible? It is an upflown system fairly modern, i'm unable to tell the brand for i'm away from home. Please advise thanks.

Reply:

A cracked heat exchanger is unsafe and should be replaced. I can't guess why that'd cause the furnace to cycle on and off; they may be separate problems.

Question:

(Dec 24, 2012) Robin G said:
I have a wood stove in my basement (family room). This stove heats 2/3's of my house nicely (via convection up the stair way. However, the family room is unbearably hot and the far end of the house is 5 degrees cooler than desirable.

I am thinking of running some duct work with an inline fan (air boost fan) to pump the hot air from my basement over to the other end of the house. The duct inlet temperature will be approximately 120-130 deg. F. The duct insulation will be R5. Length of duct run is approximately 90 feet.

Question: How many CFM and at what static pressure should the fan be rated for? (room size = 14 x 14 ft)

Question: OK to leave the furnace shut off?

(Dec 29, 2012) William Wotton said:
I have heard that it is not good to leave my oil furnace shut off for extended periods of time...I am heating with wood & would like to keep my furnace as a backup but do not want to keep it on for the sake of keeping it on.

Reply:

The concerns are:

1. moisture causing rust in a furnace that never is heated to dry out - more of a concern for steel furnaces than cast iron units

2. solidification of soot and creosote deposits making the unit hard to clean

Have the unit thoroughly cleaned before shutting it down; inspect for and fix any unusual moisture sources.

Question: diagnosing furnace noises: a humming

(Nov 5, 2014) Af said:
Low pitch humming now that heating is on. Furnace is in basement and noises come from 2nd floor

Reply:

Check for a failing transformer or motor.

See these articles

• NOISE AIR CONDITIONER / HEAT PUMP
• NOISE DIAGNOSIS, HEATING SYSTEM
• NOISE, DUCT VIBRATION DAMPENERS
• NOISE, HEATING SYSTEMS

Question: Lennox Conservalor III forced hot air furnace shuts off too much

(Feb 15, 2015) RLongfield3rd@hotmail.com said:
I have a gas Lennox Conservalor III forced hot air furnace. Sometimes it shuts off and the temperature drops quickly. When I reset the Carrier thermostat installed by Con Ed, the fan will go on, but no heat. When I go down to the furnace I can hear/see the electric starter spark, but the furnace does not ignite. I then shut off the switch next to the furnace for a couple minutes and then switch it back on and the spark begins again and usually the furnace fire up, but sometimes it takes a couple of times.
This problem occurs sporadically, but during this cool spell it has happened twice in two days. Obviously, if we ware on vacation then we would have suffered broken water pipes etc.
One addition point is that the ‘clean air filter’ message is always present even though I change the filter.
I did inform a company to come in to check it. They went through the same procedure and then just opened exhaust pipes and cleaned them out, but after awhile this problem reoccurred.
Is there something between the spark and ignition of the gas that could be the problem?

Reply:

Sure; it's time for a detailed inspection by your heating service technician. If the unit is not igniting there may be a burner, fuel, or control problem. Don't force the system to ignite as you may blow yourself up.

...

Continue reading at FURNACES, HEATING - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• FURNACE CONTROLS & SWITCHES
• HEATING FURNACE INSPECTION GUIDE
• NO HEAT - FURNACE
• FURNACE OPERATION DETAILS

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FURNACE HEATING FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING FURNACES

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