Brian Allen

Is the 6" system enough for that size of building, or do you wish it was 8"?

Yes, I plan to have a cast cover that will seal off the feed tube once the fire dies down.

Thanks!

Thanks, Brad.  It's a steel building with no attic and the plan is to have the RMH be about 12 from the closest outside wall, so it's either bring in combustion air through the roof or through the various leaks in the building (which are few, just around the 2 garage doors and man door).

I think I'll still try it first without. I can always add it later.

Is your RMH an 8" system? How does it do heating that big of a building?

Graham Chiu wrote:https://woodheat.org/the-outdoor-air-myth-exposed.html

Thanks for sharing this link.  After reading up on it I think I'm convinced to build and run the RMH without any outside combustion air (aside from what gets naturally pulled in around the doors). I can always revisit the issue if there is a problem to be solved.

However, reading that has caused me to question what will happen when I turn on the exhaust fan for my laser cutter!  It has the potential to make my RMH way less rockety, or perhaps even draft the wrong way.  It's a pretty powerful fan and is moving a lot of air directly outside. I'll have to watch that and may have to give the laser cutter area a way to bring air IN at the same approximate rate its going OUT while the exhaust fan is on.

Thanks everyone.

Jean-Paul Calderone wrote:How tight is your steel shop?

It's pretty tight for a steel building because every joint and corner has been sealed with the 1.5" of closed-cell foam. Really the only places air is coming in or going out is around the 2 garage doors and the steel man door. There are no windows. The garage doors don't have weather seals yet, but I'm adding them.

Jean-Paul Calderone wrote:What's your motivation for providing a dedicated air supply for the RMH?

The only motivation is direct delivery of the combustion air, to keep it from pulling cold air in through the cracks around the doors and across the shop space to the fire.  I have a big laser cutter in the shop and when the exhaust fan (one of the fans used to blow up residential grade inflatable water slides, going out through 4" duct and moving quite a bit of air) is on in the winter you can noticeably feel the temperature drop, like 10 or 15 degrees in a half hour.  I was hoping to avoid the same affect (though far smaller compared to the laser cutter exhaust fan) with the combustion air draw.

I have a 42' x 60' steel shop with 1.5" of closed-cell spray foam insulation on all walls and ceiling. I'd like to build a RMH (probably 8") to heat it and am getting the general design together.

I'm planning to run triple-wall 8" stove pipe straight up near the barrel and out the roof (a little over 15' from floor to ceiling, plus another 3+ feet outside to get above the roof peak).

Could I cut into the outside of the stove pipe near the barrel, just the outside layer, and basically use the outside ring of the triple wall pipe to bring in combustion air?  Or is that a no-no or otherwise wouldn't work (it would be fighting against the up-draft due to the warmth of the air in that outer ring, so possibly it would be counter-productive and actually try to PULL air rather than bring outside air in).

The other option is a dedicated air intake, but that would mean a separate 15 foot run of pipe up the wall.  The RMH burn chamber will be 12 feet from the side of the building (see the attached image) and about 20 feet from the front of the building, so the only real way to get combustion air in (that I'm aware of) is through a vertical pipe, like the chimney.

Would the intake air pipe need to be the same diameter as the chimney, 8"?

Thanks!