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Can an 80% efficiency, draft hood, 40k BTU, water heater be vented through a 2x10 wood rim joist with painted cedar siding? Assume proper pipe sloping.

The termination would be roughly 2 feet above ground (knee height). The house is colonial and the eaves/soffit are about 25 feet up.

Does a Type B double wall pipe make a difference? How far from the siding does the pipe have to extend before terminating? If it can go out the rim joist then do I have to terminate above the roof line?

Why am I asking this?

It currently vents through a chimney but it would be nice to demolish the chimney. The water heater is fairly new and works really well; even during power outages!

If it makes a difference, I live in Central NY.

MonkeyZeus
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2 Answers2

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4" B vent requires 1" to combustibles and has an OD of 4.5".

So, can you put a 6.5" hole in a 10" rim joist? IDK, the rule for joists is one third their depth.

I wouldn't butcher a hole that big for an 'eighty'. When you upgrade to a power vent it will be a 4" concentric, or two 2" holes.

Mazura
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That may be why it was done that way in the first place. Just be cognisant of the minimum rise per foot then exceed it when you replace it and it should go great. Keep the 90s to a minimum, there is a maximum you can use.

This was published in my water heater instructions. It is probably correct but it must be checked with your local building department to be sure. Sorry I do not know put it in a table. These are maximum values.

Allowable Elbows & Lengths for Direct Vent Gas Water Heater Exhaust

With 1-90  3" = 35'  4" = 80' 4" 
     2-90  3" = 20'  4" = 75' 
     3-90  3" = 15'  4" = 70' 
     4-90  3" = 10'  4" = 65'

Many localities require the vent to be through the roof if there is no chimney. They also state it must have an approved cap on the pipe and it must be above specified roof line heidghts. Your best friend in this would be your local building department.

isherwood
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Gil
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