[skypilot73]

I have an older furnace (20+ years) and it is keeping us up at night. We had some extra ducts put in when we finished the basement and at the time we were right at the edge of what the furnace could run (it is approx 55% effecient).

The house is always cool and not a lot of heat reaches the vents that are farther away from the furnace. The furnace kicks on and off all night and I haven't had a solid sleep since it went below 0. The furnace is directly below my room so when the furnace kicks on it sound almost like a small explosion it is very loud and aggressive. It will run for 30 seconds and kick off, then 30 seconds later it explodes back on.

Any ideas? My thermostat is digital and it is located on a wall below the attic. I wonder if we have a lightly insulated attic that a draft is confusing the thermostat?

Please Help

Dan

[hvac1000]

Could be the thermostat.
When was the last time you replaced your air filter?
Sounds like it might be going out on the high limit? Is the blower motor working?

[acetc]

This explosion could be caused by delayed ignition perhaps pulling the flame away from the thermocouple and shutting down the burner, delayed ignition may be caused by dirty burners or rusted burners. A twenty year old furnace would use a thermocouple and probably have a pilot relite ,if you watch the lighting of the burners you will notice the delayed ignition, just don't stand too close. Good luck ,Mike

[skypilot73]

I replaced the air filter just last week - what would the blower motor sound like? I assume it is working.

The delayed ignition sounds probable, but I am not sure what the cause is - I replaced the thermocouple 2years ago with a burner relight. We went from a orange flame to a blue flame at that point.

[acetc]

The delayed ignition means that the burners are not lighting fast enough and the gas builds up in the burner compartment until it lites and explodes, this condition is normaly caused by dirty burners, the burners would need to be removed and cleaned with all rust removed then reinstalled. Mike

[skypilot73]

Okay that makes sense how do I get access to the burners? Is that for professionals only?

Thanks

Dan

[skypilot73]

One more thing. I just went down to the furnace room and there is a very large cold draft along the base of the furnace. The cement floor is ice cold. It is -10c outside. The furnace flame is not vertical it appears to be blown off slightly to one side (perhaps from the cold air draft). Would this be normal or is my cold air intake having issues? The furnace is not on right now.

Dan

[hvac1000]

You should have your furnace checked by a professional. It could be the heat exchanger is cracked causing the flames to be offset.

[skypilot73]

Any issue with carbon minoxide concerns - we have detectors

Thanks

Dan

[hvac1000]

As proven many times carbon monoxide detectors (residential hang on the wall types Plug in or battery) are not to be taken as absolute proof in the diagnosis of cracked or damaged heat exchangers. As found by testing many home owners think they are safe when they are not. Many detector manufactures are in the process of dealing with lawsuits for failure of there equipment.

A 20 year old furnace is a prime candidate for cracks etc. Usually a once a year professional test is accepted as a minimal service or furnaces over 5 years old and sooner depending upon the manufactures heat exchanger failure rate. Any company that comes to work on your furnace should check for problems. If they do not have the equipment to do the testing with them call another company.

[labman]

Maybe you need to back off the furnace and look for cold air leaks into the basement.

Take a good look at the blower. See if it spins freely. You should be able to hear it come on a few minutes after the burners come on. If you don't find a problem you can fix by Wednesday, it may be time to call a professional.