Smoke puffing out of furnace door

How old is this thing?
KNow the make and model?
Is this a new problem or has it been going on for a long time?
This is a wood furnace?
When was the chimney last cleaned?
Are you burning dry seasoned wood (split and stacked in a dry location for about 2 years for hardwoods)?
What kind of chimney does it have? size / style?
How talll is the chimney?

Crack the feed door open a little for about 10 to 20 seconds, then open it up. When its opened up too quickly, it allows for too much air and it ignites causing the mini explosion. It works for me with my furnace. If opened too quick, the same thing will happen to me.

"I think its more prone if the wood is damper than this, maybe 1 or 2 not-so-well-seasoned pieces. Its only in this warm weather when its not roaring so much all the time. Occurs when its smouldering more".


Sounds like the problem. More draft needed.

You could have a low pressure in your basement. Lower than outside anyway. If you have any wood in there that has a lot of moisture in it all the energy of the fire goes into boiling the moisture out of the wood and the flue gasses become a lot cooler. With less fire (smoldering wood) you also have cooler flue gasses. With cooler flue gasses comes less draft and with less draft and a negative pressure in the room smoke will spill into the room.

I agree with Laynes, crack the door open for at least 10 seconds. But with my furnace, the most important thing is to make sure the damper is open any time you open the door.

I forgot about that, you will know right away if the stack damper is closed. I keep mine open all of the time now. I finally realized I didn't need it. I use a baro.

What's happening, Dean, is that when your air supply shuts off, an oxygen-started gas mixture is created in the firebox, at least until the fire has a chance to adjust to the new, oxygen-deprived environment. If you open the door, it puffs out and ignites in your face. From your description, though, it sounds like it's puffing when you don't have the door open. What's happening in that case is that you have an air leak somewhere that's letting in just enough oxygen to cause a series of small explosions in the firebox. They blow exhaust back out the air intake and into the basement.

You need to either find the source of the leak and correct it, or rig up your air inlet so that it never closes completely, thus never letting your furnace become oxygen-deprived. The furnace is designed to operate with the air completely shut off, I'll bet. That's because if you can't completely cut off the air supply, you may not be able to control the temp of the furnace, especially when there's strong draft.

I'd try to find the leak, starting with the gaskets around the doors. You should also check the gaskets for the draft blower (if you have one) or the seal around the oil burner backup, if it has one of those.

In my experience, this can be an intermittent problem, depending on the draft.