[Muadi]

Hi,

My 1992 furnace acts up once in a while. The pilot light works fine. Cleaned and maintained burners. Over-all, the furnace is in good shape.

On cold, damp, high-humidity days, I have my problems. When the furnace starts up, it fires up the pilot. The pilot burns for about 1 minute. After that, the main gas flows, and the burners light up. The problem is with the exhaust. The exhaust begins to bloil-over into the furnace room, instead of going up and out the exhaust pipe, up through the chimney. I put my hand on the pipe, and it is cold. Colder than ambient. What I am noticing is that the cold, heavy air from outside is coming down the tube into the furnace area.

I'm guessing that the job of the pilot light running for about 1 minute is to 1) get ready to fire the main gas up; 2) heat up the flu enough to operate properly. What I am finding is the heat rising from the pilot, through the flu, is not enough to overcome the cold air coming into the house. The cold air is winning the fight.

So, when the furnace fires up, the exhaust has no where to go, and comes out the front of the furnace, sending my co2 detectors into a frenzy.

This is not an everyday occurrence. 2-4 times a year when the environment is as described.

I have had thoughts of trying to find some high-temperature heat tape to apply to the exhaust tubing, to try and pre-heat it?

Any thoughts? Thanks in advance. :)

[hvac1000]

You know what your problem is for sure but how to correct it will be a trial and error process one your part. One thing you can do is to stop the negative pressure in the house. Other household items dryers/water heaters/bath fans etc are drawing air out and it is a possibility that the replacement air is coming from the furnace flue as a down draft. At least yours is just a problem every once in a while. I have seen this many times in homes that the furnace will do it all the time.

[Muadi]

I'm sure there are other things that will cause the air to leave the house, but the only one I can think of is the dryer vent, which is upstairs. The furnace is in the basement. Cold air falling, warm air rising out the dryer vent? Interesting idea.

Is it done/recommended/etc to put a dryer type flaper valve on an exhaust vent for a water heater/house heater in the chimney area?

That would help to slow down any flow, but certainly may cause other issues... thoughts?

[hvac1000]

Is it done/recommended/etc to put a dryer type flapper valve on an exhaust vent for a water heater/house heater in the chimney area?

NO NO and NO. I hope that is clear. No obstruction of any kind unless approved shall be placed in a vent for water heaters or furnaces. There are companies that make power venters with block off devices but you do not want to go there.
Your furnace is a 1992 and close to needing a replacement (16 years old) when the time comes just get a high efficiency one and your problems go away.

[Muadi]

OK,

Thanks for the advice.