This brief period of pressurization is followed immediately by extreme depressurization, as the explosion consumes all the available oxygen, and another gulp of air is pulled down the chimney, causing the process to repeat. When this pocket of air hits the fire, a mini-explosion occurs, and the resulting sudden extreme pressurization inside the firebox forces smoke out through the draft control, door gasketing and other tiny openings that exist in even the most “airtight” woodstoves. If strong enough, this vacuum will sometimes reverse the flow inside the chimney, pulling a “gulp” of air back down the flue into the firebox. If you cut down the supply of air too abruptly, the fire instantly consumes the available air, creating a powerful vacuum inside the stove. When you have a rip-roaring woodstove fire going, and a chimney charged with rising superheated exhaust gases, the air flow through the firebox is considerable.
Will the flue solve the puff-back problem?Ī: Chances are your back-puffing episodes aren’t being caused entirely by the lack of a properly sized flue, although the extreme updraft that can be created by an oversized flue could certainly be a contributing factor.
The chimney is very tall and oversized for the stove. Q: Last year I was experiencing puff-backs, particularly on cold evenings, when I set back the fire unit for the evening.