Venting RMH

[rjdudley]

A question about venting a RMH:
Once the exhaust pipe goes outside is there a minimum height needed? I know regular stoves should be 3ft above the roof line, but, that would require about 15-20 ft of stack!
How did you guys vent your? Any photos I could look at?
Thanks
Ray

[matt walker]

Ray, mine goes into my existing masonry chimney, so it's venting above the roof peak by a few feet. Ideally, you are going to want yours up there above the roof peak. The reason is to keep wind influenced pressure differences to a minimum. Rocket or not, if you have it below the roof line and there is wind coming from that side of the house, it's probably going to blow back and flame out the feed at times due to high pressure on the windward side and low pressure in the lee of the house. You can certainly try starting with the exhaust lower than the roof line, perhaps your house is set up where there will never be high pressure on that side, but as a general rule above the roof line with a witch's hat or charlie noble or rotating vent or some other pressure equalizing cap is best.

[Oddmar]

By the way, Ray...

As i just got done posting in Manny's thread, you'll need to INSULATE the exhaust pipe outside the house all the way to the top. Ianto and others have found the exhaust gasses are so cool by the time they exit the bench, if they hit a cold pipe they just chill down and stop rising. Which will choke your RMH.

Before you start whimpering at the thought of having to mortage your home to buy that much insulated stovepipe, i made mine by putting a 10" diameter duct over my 8" diameter exhaust duct, then stuffing the 1" gap with cellulose insulation...carefully, to keep it uniform all the way around. MUCH cheaper.

[rjdudley]

Oddmar, that's a great tip! Thanks. I wonder why you don't see much discussion of that problem come up more often? It seems kind of important.
Do you think that solution would work for the wall thimble as well? I was just going to shell out $40 for an 8" thimble, but, maybe after rethinking it I could just do the same thing.
I would have to figure out what to do about the elbow/tee that's outside as well. And you guys are right about the cost of that insulated pipe! That's nuts.
I could always buy Roxul batts and use that.
A friend suggested GreatStuff Fireblock, but, after reading the comment section I've decided against it.

[mannytheseacow]

How's that rocket coming, Ray?

[rjdudley]

Things are moving along nicely!
I'm not sure exactly why I haven't been posting, laziness I guess, but, here are a few photos of our progress:







Cobbing is slowwww work as you all know. We're trying to cob in layers, then heating it to help speed the drying.
But, we've been getting off and on rain here and that's stunting our progress.
We're hoping, REALLY hoping, to finish the whole thing this weekend.
My burns have been great. Although I seem to need to place a brick covering half of the feed tube as things really heat up. I get some fire creep and a little smoke back if I don't do it.
The other day the barrel was just over 600˚ and the vent pipe was around 100˚. I'm very happy with that combination.
Under the whole system has been EXTREMELY cool. I was really concerned, but, I think that now with the cob, the refractory pour, and the design for the air flow that things are just gosh darn great. I'm really kinda shocked. I guess I was anticipating more danger.
I still need to enlarge the exit through the wall and insulate around the exit vent, just for added precaution.
I'll add more photos, inside and out, hopefully this weekend.
Guys, once more, thank you. This sight, more than any other, has helped walk me through this build and given me the courage to do something I never thought possible. It's not a work of art, but, I love being one of the only people in the whole state that has one.
Ray
PS
If anyone has some good tips on how to make small sticks let me know It's amazing how much effort goes into making kindling size fuel.

[pa_friendly_guy]

Is there a Lumber Mill close to you? They often have cut off ends of boards that works great. My Dad had a cabin in the Mountain that was heated with a pot belly stove. He used some coal, but Babcock Lumber had a mill close and we would go down and get all the cut off ends of boards that we could carry. The sizes varied 4" X 4" up to 8" by 5" or 6" and they were mostly 1 inch boards and were all kiln dried. The sizes would work great for you. You may find a cabinet shop or other wood working place that produces small wood scraps as well. Just a thought.

[rjdudley]

That's a sweet idea! There's a mill just several miles down the road. Looks like it's time for field trip!

[matt walker]

OMG, RMH!!! Ray, my goodness man! That is looking so, so, so great. I am so happy to hear that it's working well for you. And yep, they are remarkably cool and do just feel "safe" once you experience them. All the cautionary steps along the way are to help avoid any obvious dangers and steer builders towards the safe side, but yeah, once in and running, they are a very safe feeling system. Your cob work looks great, I love the color of the clay. Man, I can't tell you how happy it makes me to see your success. You are going to have an amazingly comfortable winter my friend, just like Manny.

As for the wood, if you are needing to split small, use the tire trick. It's a game changer for sure.

[mannytheseacow]

Looking great, Ray! You have a real advantage that you can burn a little at a time to help dry it out. I have the same problem as you- I generally keep the feed 1/3 covered with a brick. I still have smokeback issues, though I've said several times.... still wet, not that cold out, cold bench, etc.... I have found mine runs great when I put shorter wood horizontally in the burn chamber. When I put larger wood down the feed tube I get creep and smoke back.