Why the downdraft?

[velvetfoot]

I've been experiencing some downdraft upon startup recently, like this morning. I can feel the cold air coming down the stack into the house. Cracking open an adjacent window helps. Opening the basement door did nothing. I don't sense any cold wind coming down the oil burner diffuser flap (or whatever it's called) in the basement. It goes away once things are warmed up, like after a piece or two of newspaper is burned. Annoying because smoke comes in the house if above routine is not followed. There were no mechanical draft sources on. Chimney 30' made of 6" stainless liner in a heatilator stack (stove is an insert) enclosed in an insulated chase. House is 2 floors, insert on first. Outside temp was 28F, 1st floor 59F, and basement 55F. I would think it should be cool enough for a natural draft. (Just thought of something: weatherstrip attic hatch - don't think that can be that much of a factor though - it's lying flush with insul on top.) House is a couple of years old, so should be pretty tight, generally.

The first time I got smoke in the house was a little disconcerting. Now, I take the above steps if I feel a cold breeze. Maybe it will be an occasional thing...just got the insert in March.

Opening the window, etc is an incremental hassle.

Any ideas?

 

[elkimmeg]

A lot of times heat would excape up that chase and it was allowed to from you home of the prefab fireplace they are notorious for leakage even insulated chases many times no insulation was placed above the prefab it was to prevent it from over heating anw warping. The chase may be lined but the ctritical space above the insert many times was not.
Insulatind does twojobs helps the heat in but also holds cold temps. Your insulated chase may be doing the job of keeping in the cold.

Stack effect also could play an hand you you have recessed light upstairs and weather stripping the pull down also will help look for leaks in the second floor ceilings to reduce the pressure leaks

 

[tutu_sue]

Elk is right - you could have negative pressure caused by air escaping out of the upper part of your home - recessed lights, attic hatches and exhaust fans can be culprits. As it gets colder out and the temperature differential gets greater, you will notice less of a downdraft. Cracking a window near the stove and warming the chimney with newspaper will correct the flow quicker and cut down on smoke from backing into the room.

 

[begreen]

If the house is pretty tight, how is it ventilated? Is there a whole house ventilation system running?

 

[velvetfoot]

It is ventilated with windows.

 

[wg_bent]

I had this recently. traced it to the attic fan.

Once plugged, no more downdraft.

 

[begreen]

It is ventilated with windows.

A couple years old should be requiring additional ventilation. But you are saying there is no other vents, or heating system air exchangers etc. Most unusual in our neck of the woods for a new house.

 

[velvetfoot]

I'll weatherstrip that attic hatch.

The house has oil hot water baseboard heat and no A/C.