# I have a lot of BTUs, is my exhaust vent the right size?



## double-d (Apr 26, 2011)

This is a pre-existing zero clearance gas fireplace with a 10" Class A double-wall pipe. While helping a friend replace his chase cover I thought the flue looked a little small. The fireplace opening is 44" wide and 36" height, 30' tall chimney.
When determining the exhaust size of a 150,000 BTU gas fireplace (if that makes a difference), do you use the same type of calculation as if you were using a wood fireplace? Width x Height and divide by 10 or 12 depending on the chimney height? Can a external exhaust fan be used to make up the difference if the pipe is to small?


----------



## DAKSY (Apr 26, 2011)

This is a pre-existing zero clearance gas fireplace with a 10" Class A double-wall pipe. While helping a friend replace his chase cover I thought the flue looked a little small. 

*Are you sure it's Class A? Most ZC boxes - wood or gas - are NOT vented into Class A chimneys. Is this a factory built gas fire place or a factory built wood-burning fireplace converted to a vented gas log set? See if you can get the model number off the rating plate to help us help you. There should be one on the box & if it has a gas log set, there should be a plate attached to the gas valve.
*

The fireplace opening is 44" wide and 36" height, 30' tall chimney.
When determining the exhaust size of a 150,000 BTU gas fireplace (if that makes a difference), do you use the same type of calculation as if you were using a wood fireplace? Width x Height and divide by 10 or 12 depending on the chimney height? Can a external exhaust fan be used to make up the difference if the pipe is to small?

*If it's a Direct Vent (DV) gas fireplace, the chimney size is specified by the manufacturer, as is the venting configuration.
We are gonna need more info before one of us can answer you correctly *


----------



## double-d (Apr 26, 2011)

Thanks Daksy, I was a little quick, and didn't have all the information, and may still not. It is a brick and mortar chimney that has been added to, they installed a transition plate on top of the chimney, then went through the rafters and roof with Class A and built a case to cover it.
This was an existing setup when they bought the house, I'll see about the other questions and see if I can get some pictures.


----------

