I’m installing a vented HWH for a heated slab system in my workshop. Location is next to an exterior wall. Don’t really want to put the 3″ class B up through the attic and steel roof because it will be very difficult to access from the inside for fireproofing through the blown in FG. Trusses are on 7′ 9″ centers and I didn’t put a catwalk in for access to this space.
So I’m considering a through-the-wall approach with a listed wall thimble. OK so far, but can I just leave it at that? 3″ class B through the wall, an elbow up with short vertical extension and rain cap that will terminate a few feet under the soffit? Or would I run into back draft or insufficient draft with such a short verticle run? I put a direct vent sealed combustion space heater in that way according to the instructions. Actually, the space heater vent just runs right out the wall about 8″ with no vertical upturn.
There are no windows or doors at all on that side oif the building.
Or, should I extend the exterior vertical run through the soffit and roof steel (flashed, of course) with fire stop (4″ or 6″ galvinized) to protect any stray pieces of FG that could get hot against the class B? And if so, how far should it extend vertically above the eave. This is a 4-12 pitch with 16′ of run between ridge and eave. This I could access, cut holes, flash etc, from a ladder outside.
I am concerned with snow (SE MN) sliding off the roof and taking the vent with it, so don’t want to hang the vertical run off the gutter.
Thanks in advance for your advice.
Replies
I don't know that an elbow and cap are necessary. I saw one recently with a special cap assembly that bolted flat on the wall. Don't know the brand. It looked nice. But, that may have been specific to the brand and type of water heater. As far as under the soffit, at least around here, that is allowed as long as it is more than 3 feet from a window. If it is considered a chimney and not a vent, it has to go up 2 feet higher than any part of the roof within 10 feet. Tall.
Many manufacturers make what's called a sidewall vent kit for just this application. These kits are tested and approved for proper safety and operation of the equipment they're attached to. Call your local distributor for more information.