Wednesday, October 15, 2008

Doesn't Suck Hard Enough


As I wrote in my post about this house's heating, the previous owners installed a wood stove insert into the first floor fireplace.  The darn thing billows smoke and ash into the room whenever the door is opened for reloading. 

I've been following the instructions: Before opening the door I fully-open the insert's air inlet and shove the outlet baffles out of the way. But even so, even after one week of operation everything in the room is getting ash all over it. 

So I had a chimney sweep come out and see what's up. 

Turns out that while the chimney flue's wide throat works well for a fireplace, which is inefficient and sends vast amounts of hot gases up the flue, it's far too fat for an insert. Inserts put out less exhaust, and cooler exhaust,  too, than a fire. This is because they are so much more efficient at getting the heat out of the fire before it goes up the chimney. 

As a result, they are unable to develop much draw in a fat chimney. The problem is exacerbated by how tall our chimney is: it rises two floors before climbing up through the crawl space then up above the roof. That's just too much volume of air to expect a fire in an insert to get into motion. 

Which explains why the fire and smoke billows out when the door is opened: it's probably easier for the smoke to go into the room than up the flue, especially when it's really cold outside or when wind is fluttering across the flue opening. 

The solution is to put a liner--essentially a stainless steel stovepipe--down the flue to the opening on the top of the stove. The sweep said it's a straight shot down to the insert so it should be an easy job. 

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