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QUESTION:Hi I need some advice. I have a friend who is installing a hot water heater
in his garage this weekend. His vent will go basically vertical for about
25 feet. He wants to make his own "B" vent with regular single wall venting
by placing a 3" vent inside a 4" vent. The vent will terminate with the 4"
cap below the 3" cap, the 4" cap having a 3" hole cut through it so that the
3" pipe can rise through it and terminate above in its own 3" cap.
The reason he wants to use this system is so that the exhaust will exit the
3" vent and (in theory) the outer 4" in vent will draw down fresh air, warm
up as it comes down by the exhaust gas, and provide -warm- fresh air needed
for the combustion air.
My concern is 1) not code and may void his insurance policy, and 2) because
the air in the garage is often warmer that the outside air, (in the winter
anyway), the warmer air will rise in the 4" tube and will do the opposite of
what he wants.
What are your thoughts on this?
ANSWER: Should have told him to buy a State Water heater, they sidewall vent with a
concentric kit and are approved that way. I believe it is a 4 inch vent
inside a 6 inch intake.This 4 inside a 6 suggests the area of the annulus is
equal to the area of the vent. Sounds like he is mimicking a trailer
furnace.
You are correct that he will void his insurance policy as an appliance is
being installed in a manner that has not been approved.
He is right about conserving energy however it is peanuts. If combustion air
is drawn from the garage, cold outside air will infiltrate in from the
outside to replace the air going up the stack.
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