Latest Discussions : HVAC


08:32AM | 02/04/05
Member Since: 02/03/05
3 lifetime posts
Can someone please help me - I have a Coleman Propane furnace - 6 years old - It has just started making these loud popping noises which sounds like someone hitting a metal file cabinet..This only occurrs after the furnace has actually ignited and is running then about 1/2 minute or so it POWS/POPS and then runs fine as always , then when it shuts off completely it POWS/POP again in about 1/2 minute... This is very worrisome to me and scary particularly at nite... Help!!


06:29PM | 02/07/05
Member Since: 12/16/04
54 lifetime posts
Could be that the air filter is so dirty its causing the sheetmetal to colaps when the blower starts and stops.


06:56AM | 02/08/05
Member Since: 02/03/05
3 lifetime posts
Please clarify about the air filter - is there an additional air filter inside the furnace that a technician would need to change or are you speaking of my air filters that I change on a regular basis (they are inside my "shutter panel" on the front of the furnance. Please let me know asap...


04:08PM | 02/10/05
Member Since: 12/16/04
54 lifetime posts
Your COleman furnace has the filters on the face is that right? or is there a flat panel and behind the panel up above the furnace inside the sheet metal is where the filter is? If the filters are in front of the furnace on its face, you might try running the furnace fan motor without the front grill on and see if the popping still occurs.


06:40AM | 02/11/05
Member Since: 02/03/05
3 lifetime posts
Hi - I have filters attached to the inside front panels which I change on a regular basis... I removed the panels with the filters and let the furnace run with out the "door panel" to see if the popping noise would stop... No it hasnt - still the same noise - Can you clarify what you mean by air filters inside the top of furnace ?? My original question was:is there an additional filter in the furnace besides the filters I change on the panel doors?


08:21AM | 02/12/06
Member Since: 02/11/06
1 lifetime posts
I have the exact same problem with my furnace - loud bang noise when the furnace shuts off - this happens every 5-10 minutes and i am really uncomfortable - please let me know how you solved this issue - is it to do with the filter only ...


07:44PM | 01/01/13
I was told that when this happens on my furnace,it could be due to a buildup of gas before the pilot light actually ignites the burner(s).


03:09PM | 12/01/14
I have the same thing going on! It started this year and when the noise happens, the pilot light (flame) goes down and then back's where the gas filters into the system in the front.


11:43PM | 03/06/16
We replaced the furnace,it's a heating oil furnace with boiler.The first time starting it ,it ran a little then it popped ,and we shut it off.Anyone help me out as far as what made it do that?


08:52AM | 10/07/18
Check the temperature of the duct at the furnace after it shuts off. It it is hot, you likely have insufficient air circulation and unspent fuel may be combusting without ignition. Almost all furnaces are wire to MED fan for heat cycles. When a furnace is onstalled on ground level rqther than in a basement, there is additional airflow restriction on the ductwork, and rewiring the heat fan to HI in the blower cabinet will improve heating efficienct and likely eliminate the popping sound after shut down as well as reduce the temperature of the ductwork the furnace.



08:55AM | 10/07/18
As you can see from my typing issues, perfection needs to be earned with this wave of grads.


07:44PM | 10/08/18
There is a term known as puffback, similar to automotive backfire. The furnace's manual specifies a temperature rise that needs to be maintained if adjusting circulator blower speeds. On a 5-speed blower it can be also set to MED-HI. Of course, there may be other problems such as a sooted combustion chamber and exhaust, dirty nozzle, popping ducts, etc. for which this is not the solution although definitely worth mentioning.


08:28PM | 10/08/18


11:19PM | 10/08/18
In addition to the above, inadequate ventilation could be starving the oil furnace of oxygen, causing excessive soot to accumulate. This may be the fault of the homeowner making the house air tight to better insulate. A fine balance of energy efficiency and adequate ventilation is tricky at sub zero temperatures, and especially sub -30C.

Older houses provided adequate ventilation via infiltration through leaking windows as well as breathers in the masonry and other places. This may need to be supplemented by a combination of slightly open window(s) and ventilation/draft blower(s) in a newer or renovated home. It is good practice to control the vent fans with dimmers/rheostats or timers for fine tuning.


09:32PM | 10/13/18
In my case for my Lennox Elite oil furnace the problem surfaced after installing a filtrete allergen filter. I usually run all my furnaces with a low restriction (econo duststop) filter. Prior to the problem the furnace was running with no filter and there was no popping noise after shutdown.

I installed the filtrete because none of the local retailers (Canadian Tire, Home Hardware, etc) had stock of the econo ones.

I suggest running the furnace without a filter as a first step in diagnosing this type of problem.


09:34PM | 10/13/18
Sorry I meant Walmart not Home Hardware. I managed to find a 3pack of dust stops for 5.99 at Home Hardware. Oh my word . . . I was seriously thinking of getting a new furnace!


01:22AM | 10/14/18
One of the bloggers in this thread has a good point about latent heat buildup causing a second fan cycle after furnace shuts off.

This is the problem with increasing blower speed to compensate for other problems such as a restrictive filter or duct.


03:51AM | 10/14/18
Another cause could be the fan off (delay-off) setting on the control board being too short. This is the amount of time the fan runs after the burner shuts down. With the Lennox, the factory default is 90 seconds. The dip switches can be reconfigured to increase this to 120s or 150s. With this increased, the 2nd fan cycle and popping noise may be eliminated.


11:12AM | 01/07/19
I had puffback after burner shutoff when using pink dyed farm diesel. It went away when I switched over to clear diesel.

"What you pay is what you get".


11:57PM | 01/15/19
Popping ducts may also be cured by eliminating the horizontal gradient throughout the house. This can be done with 2 inexpensive digital thermometers placed at opposite ends of the house. If the vent grilles cannot be adjusted to get equal readings, the house may have a missing duct.


04:31PM | 04/14/22
It’s probably not puff back but actually the blower compartment door popping between a concave and convex shape. Ignition sequence starts then fan turns on and depressurizes the blower cab sucking the door in. Design temp reached and burners shut down then fan shuts off. Once it winds down enough pressure equalizes and door pops back out.

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