doublte walled flues
There is virtually no oil fired equipment in my area, so I all my
experience has been on gas units. The main thing about double walled "B"
vent is allowable clearance to combustibles. It is generally 1 inch with
double and 6 with single. With single wall, a 4 inch pipe would need to
have a 16 inch diameter hole in a roof. Larry
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