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Furnace Change-out

If it’s time to replace your old and rusty furnace you can get all the info you need almost instantly in the chapter from my Ductwork Installation Guide book below!

During 30 years in the ductwork and furnace installation and replacement business I personally installed and replaced hundreds if not thousands of furnaces and in this chapter you can find everything you can think of!

The chapter is written for the basement furnace replacements and covering:

  • Replacement of the 50% to 60% eff. furnace with 80% eff. furnace
  • Replacement of the 80% eff. furnace with 80% eff. furnace
  • Replacement of 90%+ eff. furnace with 90%+ (95%, 96%, 97%) eff. furnace

If you are replacing an 80% or 50 % to 60% eff. furnace with a 90%+, then you may need to purchase two additional chapters from my Ductwork Installation Guide book that are covering PVC venting and condensate lines installations. Both chapters and much more you can conveniently find on this page.

Questions? Comments? Type them on this page.

59. Furnace Change-out – the chapter is dedicated to the furnace replacement part of the trade and describes everything that an installer is suppose to know.

The chapter has 72 pictures; 27 pages

Purchase this chapter at the discount price and save!  
The price is only
$11.98 (Instant Access)

The Chapter has Links to:

  • Furnace Replacement in Pictures
  • International Code

PDF files:

  • A Guide to Residential Wood Heating
  • Proper Subcooling Charging Techniques
  • Installation of Gas Piping
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List of Noises 5:

Chirping noise 1
Clicking noise 1
Clicking noise 2
Explosion sound 1
Clacking noise 1
Boom sound

If your Atwood 8525-IV furnace makes loud bird chirping periodically, then you can disassemble the furnace until you could reach both ends of the fan motor. Remove the inlet side of the "squirrel cage" and see if there is rust powder just below the motor shaft. Squirt some oil it into the bearing, rotate the shaft and squirt it a couple of more times, to make sure that you had saturated the area. Reassembled enough to get the fan to run and make sure that chirp was gone.

If you have clicking in the gas line whenever the furnace kicks on, then it could be the outside meter dial had gotten wet and was frozen. When the gas turned on (for example when the furnace kicked on) the gear inside the meter turned and the outside one stayed immobile, causing a clicking noise.

If your old furnace calls for heat, the pilot light turns on, but no hot air, after the pilot light kicks on, it makes this clicking noise, like the stove makes before it ignites, then you may need to replace the whole pilot assembly.
However, before doing that you can try to take the assembly out and use some sand paper to clean the metal strip that the flame 'strikes' or comes into contact with. Because the bi-metal surface can't tell that there is actually a flame present it's doing two things: 1) it keeps clicking, trying to establish a flame/pilot, and; 2) it's preventing the gas valve from opening, because if there was no flame raw unburned gas would be flowing into your home.

If your Armstrong ultra sx80 furnace that has an electronic ignition started making a loud explosion sound upon lighting the burner. It could as if the igniter isn't lighting quickly enough and then after a second or two it lights with a loud boom (whoosh), then maybe the igniter has become loose from its bracket and its position has shifted, so the incoming gas does not see it until too much of a build-up in the combustion chamber.
Maybe also there is rust build-up at one of the burners, the one near the igniter and that is deflecting the gas, so there is a delay in igniting it. Low gas pressure could also cause this problem or you may have delayed ignition.

If you noticed that when there is a call for heat, your Carrier Infinity furnace goes through it's pre-cycle and before the igniter glows and lights the flame and before the actual circulating fan kicks up to a higher speed there is a noticeably loud clack, then it could be a throttling valve on the outlet side of a two-stage gas valve.

If your furnace is making some terrifyingly loud booms within about 60-90 seconds, with ticking in between: tick...tick...tick....BOOM...tick...tick....tick...tick...BOOM... and then the blowers will kick in.
Sometimes it only booms once, sometimes 3+ times. Then the burners are dirty or out of alignment/pilot is dirty/gas pressure is wrong. If it gets bad enough the flames will roll out the front of the furnace and burn up all the wiring and do major damage.

List of Noises 6:

Boom sound
Clicking noise 3
Clacking noise 2
Chattering noise
Ratcheting sound
Groaning noise 2
Hissing/screaming noise
Horrid sound

If the pilot light on your furnace going out and you have to relight it about every 2 or 3 days, If sometimes when the heat is on, you may hear a big boom sound from the furnace.
Then for some reason the pilot may not be close enough or high enough to the gas flow output on the burners to ignite the gas as soon as the gas valve opens the flow. The pilot is apparently strong enough to keep itself burning by the gas control valve. Maybe a draft is blowing the gas away from the pilot.
Anything that will momentarily suck the gas away from the pilot flame like a small vent suction or a cracked heat exchanger small suction can give the gas time to build up. A dislocated pilot tube is another. That's all it takes to cause an explosion.
A few seconds later the "on" gas that did not light immediately, accumulated greatly, and finally found the pilot flame then it make a boom. That was an explosion and it blows out the pilot. So if this is a case you need an inspection of the pilot lighting or it could be rust flakes on the burner clogging the gas output right at the pilot area. Vacuum the burner tops and area anyway. If you do have a lot of rust make sure you inspect the burner chamber for cracks and leaks.

If your 1986 vintage Rheem furnace when heat is called for, often it works normally, but often the gas valve will click, the pilot comes on (electric spark ignition), and the burner will fire, then the gas valve starts clicking on and off, very fast, randomly (no cadence), and the unit will shut down.
Or, it starts clicking madly as soon as the pilot lights and the burner will not fire. Or some variation of this, but always the gas valve is clicking madly. Then if you do have a meter, take a reading on R and W, and see if that power is steady. If turns out it's steady, then take a reading as the gas valve, and see if power is steady. If it's on and off then it's the ignition control module. But if the power is steady, then it's the gas valve itself.

If your gas valve is clacking and chattering, also the furnace will fire up sometimes, and sometimes not, then it might need to be cleaned out the burners and cleaned the flame rod.

If your Trane furnace makes annoying ratcheting sound, then the chatter is being caused by feedback or voltage loss in the thermostat circuit and it could just be that when the humidifier engages it causes disruption in the voltage that engages the chattering relay.

If your Comfortmaker furnace makes a loud 60 Hz hum startup noise, and it may varies in pitch as the motor groans to spin up the blower (wa.....wa...wa..wa,wa,wa,wa). After a few seconds, the noise disappears and the blower continues to spin up until operating at full speed, then you may need to replace your motor with a Balder motor that is twice the weight of the noisy motor.

If your Rheem air handler that has just recently started making an odd hissing/screaming noise, then you may check out the bearings and if the fan isn’t kinda wobbly. If this is the case, then your blower wheel might be out of balance causing it to scrape the housing as it starts up. After running, it straightens out and doesn’t scrape.

If you are hearing a horrid sound coming from your furnace – it sounds like a motor was going bad. If your unit has a LED light on the control board that blinks a pattern to show what is wrong with the unit and there are 3 blinks, which mean: "Pressure switch failed to close."
If you examine inducer motor closely - the plastic wheel does spin the inside gear but it seems restricted/doesn't spin as freely as it should, then you need a new inducer motor.

List of Noises 7:

Banging noise
Popping noise
Rattling noise
Squeaky noise
Whirring noise
Whistling noise
– watch the video below
Whoosh noise

If your 30 years old wall furnace when it cycles off, it makes a series of banging noises as it cools down, then that could very well be a cracked heat exchanger. Wall furnaces are dirt-cheap, just buy a new one.

If you have noticed that your furnace is making a whirring noise: something like whir-whir-whir-whir and it does this from the time it kicks on until it shuts off, then it could be the impeller on the exhaust/inducer motor was broken making it unbalanced creating the noise.

If you turn a thermostat up and furnace clicks. Then at the actual heater is you hear a whirring motor come on. Then another click and igniter glows orange goes out and you hear the whoosh sound of the burners lighting then they go out and the whirring sound stops. Then the whirring motor you hear is the draft inducer fan, and the glowing thing is the igniter. If the burners are igniting and then going out right away, the most common cause of this would be that the flame sensor rod needs cleaned. It is just a little rod that sticks out into the flame, shut off power to your furnace and gently scrape or sand it, then turn the furnace back on and you should be good. If a flame sensor needs to be cleaned: It looks like a piece clothes hanger (as big around) and is mounted on a ceramic disk. It has 1 wire coming out the bottom. You can either try to clean it with it in the furnace or you can remove the ¼" hex head nut and remove it, and to clean it you will need an emery board or finger nail file. All you need to do is remove the oxidation from the sensor and reinstall it, and turn it back on.

If when the thermostat calls furnace to turn off and the burner shuts off, there is a squeaky rattling noise. It may sounds like it's coming from the heat exchanger area and not the blower, then it could be a new filter you put in is too thick and there's not enough air flow so the motor is working harder, and vibrates due to the higher negative air pressure inside.

If your furnace is in a mobile home and it lights off ok, but starts popping after 2 to 3 minutes then have your local licensed hvac repair guy check this furnace out. Problem might be the high temperature limit switch intermittently opening up the circuit then almost instantly closing. This caused the burner to shut down then immediately relight. Since this furnace may has a two stage gas valve, (low fire on start up then high fire on run mode). With the high limit cycling on, off, on in less than two seconds the relight is rough, always in high fire, causing the popping noise. Replacement high temperature limit switch may fix the problem.

List of Noises 8:

Banging noise
Clicking noise 4
Grinding noise 1
Growling/rattling noise
High pitched sound
Humming/whistling noise
Rubbing sound
Scraping noise
Woof sound

When your Nordyne gas furnace turned on it starts the heating coil heats up and you may hear the clicking sound for the ignition. The ignition never happens and you may hear an another clicking sound following the heating coil shuts down and the same procedure continues for 4 times and then you can start seeing a flashing red (flashes 4 times), according to the information on the back door four flashes = Ignition Problem - Check Ground. Then your hot surface ignitor does not get hot enough, it will not set off the gas. You can ohms test the coil across it's two wires, with a volt-ohmmeter. It should be about less than 100 ohms, to set off the gas. Or, you could have such dirty burners in the area of the glow coil that, it can't set off the gas in the 3 second safety allotment time.

If your furnace when the blower motor comes on  makes a grinding noise and blows the fuse, a grinding noise is usually the fan being loose or the bearings in the motor are defective. Depending upon what kind of noise it really is it could also be the start capacitor.

If you have Miller oil furnace and the blower is making a scraping sound, then it might be the screw that holds the cage to the motor shaft is loose, just lock-tighten it.

If your Armstrong high efficiency furnace is making a high pitched sound – it kind of sounds like locusts. In the fan only mode, there is no sound, then, to your knowledge, typically the inducer motors have sealed bearings. If the motor is squealing it is time for a new one. Inducers are usually sold as an entire assembly which makes it easier to replace.

If you have an old (25y.o.) GE model furnace and it refuses to stay lit. The igniter will ignite the gas, and then as soon as the spark goes out, the gas shuts down. Ends up sounding like woof, woof, and woof, then you should check the pilot orifice to make sure it is completely open. Just take the pilot apart and there are two small holes, one of which could be partially plugged. Ran chemical cleaner thru it.

If your furnace give a big bang just before the heat comes on, then you may call a gas company out to check out if the burners are out of line and not filling up with gas evenly, so there could be an excess of gas so when the burner came on it is a small explosion each time.

If you have a Carrier 58 PAV furnace that is making a high pitched humming/whistling noise that is coming from the induction motor assembly. When the motor assembly turns off, it sounds like a jet engine powering down. Then you can pull the lowest drain tube the black rubber ones on the inducer enclosure and see if water comes out (more than a couple drops) if so drain trap may be clogged and preventing proper drainage making the blower wheel become a paddlewheel.

If you have a Carrier 58PAV (12 yrs old) and it makes growling/rattling noise coming from somewhere in the inducer motor assembly. A PAV is a mid efficiency furnace with no drain hoses. You need to replace both the motor and wheel as it gets off balance. Be very careful how you handle those wheels as they bend very easy and get off balance and will create vibration and future noise.

If your furnace when it starts up making a rubbing sound. Then three screws should hold the motor and squirrel so the fan housing stays in place. You'll have the motor and squirrel in hand. There is an Allen key or locking ring pinching the squirrel to shaft, might need to pull it up a bit on the shaft. Eye ball it, spin it both ways so you know it’s not the bearings.

Is it time to replace your furnace? Fill out a Repair or Replace Report Card

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