Rocket Mass Heater for my home

[matt walker]

So, it's drying out nicely. I've had a few burns, and don't need the fan anymore although it is still slow to start, which I hope is a function of a whole lot of moisture still in the bench. It's got some dry spots, but is still dark with moisture and has a ways to go. I haven't gotten the flue run section of the bench much above 75° yet, although the barrel end jumps right up to 100° pretty quickly. Once it's warmed though, it's burning great, with good draft. I stuck the Testo in there last night when things were going well, and even with only two small sticks in there which leads to high excess air, which really hurts the efficiency number, I was still running in the mid 90% range for efficiency. Amazing. I'll keep drying and try to get a good run on the Testo in the next few days.

[ByronC]

Sounds good Matt. I like that convection bench! Planning on doing something very similar for my indoor 8" RMH build. Problem is that I've only got room for a single straight 10 foot long bench. I'm thinking of making the bench from half barrels, locating the rocket burner on one end and the exhaust outlet on the opposite end (coupled to 15' of vertical chimney).

To build in a little more "bell" ISA into the short bench, I'm thinking about extending the sides of the half barrels by propping them up on a short wall of masonry/cob. Cobcrete and rock will be the mass covering the half barrels. And there will be an air gap underneath as well, and up the back, like yours. Let me know if there are any outstanding holes in my plan.

What's your preferred method for ripping barrels? I figured that you've done enough of them by now that you've settled in on an efficient speedy way to get'er done. Right angle grinder fitted with a thin cutoff wheel, recip saw, or something other?

[matt walker]

Good plan Byron. That bell idea is good. It will put seating a bit high, but perhaps you can either bury them lower or have a raised patio around them.

I use a jigsaw to cut them. It's loud and annoying, but really quick and fairly easy. Cut-off wheel is slow and scary since the edges bind it up, and the recip tends to just grab and shake the whole thing so they don't cut. Torch is the quietest, easiest, but it is also slow and sort of a pain in the butt. Get a lot of jigsaw blades, and use really good hearing and eye protection. It kinda sucks, but once it's done, it's done.

[mannytheseacow]

I'm glad that's working out for you, Matt. So what's the story with the fan? It's up on the roof?!

I've always used an angle grinder for cutting barrels. I haven't had any issues and it's super fast.

[ByronC]

Very good on the jigsaw. Yeah, hearing and eye protection is a must. I've cut lots of 6061 over the years, and steel panels and chassises for electronics projects, with my jigsaw.

H'm, you're right on about the seating height of the bench. I'll have to think that one through a bit more.

[matt walker]

Yeah Manny, I have a 6" AC powered fan I use on my outdoor system when it's all soaked with rain after sitting a while. I just set it on top of the chimney and used it for the first couple burns to lift the moist, cool gasses out of there. I haven't needed it since, and doubt I will once things are dry.

[matt walker]

Just a quick little update here...things are drying out nicely. It hasn't been very cold here, upper 50s low 60s, so I'm forcing myself to burn a bit morning and night to dry things out, even though I don't really need to. This thing is right on the edge of working at these temps, I'm sucking so much heat out of the exhaust that it's just barely drawing enough to work. I need to keep it warm, and wait until nightfall/early morning for colder outside air temps so it flows properly. It's amazingly efficient, but that's at the expense of solid draw in all conditions. I probably wouldn't even be burning now though, if I weren't trying to dry it out. I'm sure once things cool off even a bit outdoors it's going to be flawless. So far, I'm very pleased with it. First impressions are that it puts a ton of heat into the room, isn't any more trouble to start, and I like that I can put larger fuel in it. Only downside so far is that it does have a hot door and is less safe around little ones, but no more so than a normal wood stove. I just had gotten used to having a heater that had no real burn points on the outside down low. Anyway, here's a shot of the testo from a few minutes ago. Like I said, low stack temps mean the thing is right on the edge, but man, what an edge!

[mannytheseacow]

Pretty amazing results, Matt. Just need to translate this into language that the powers that be recognize!

[matt walker]

Things are drying out. I've plastered the front of the bench, and it's still got a little drying to go, but it's getting there. I have house guests coming this weekend, so I threw those tiles on there to see how it looks and give it a temporary finish. They are just sitting there, not sure if that's what I'll do or not. I still need to finish the transition between the new and old benches, and get a top coat of plaster on the fire box area, but it's getting close. I'm really pleased with it so far, it lights really easily, and is putting the heat into the room amazingly well. That barrel end of the bench is awesome, heats right up to 100°F almost instantly and radiates into the room way over there. So far, it hasn't gotten too hot, and I sorta think it won't as it gives it up pretty readily. We'll see...anyway, here it is as it sits right now. I need to find some good cushions and covers for those back foamy things, but I think I'm gonna like this. I do intend to build a little back rest that keeps the airflow open along the wall, but that can wait.

[pa_friendly_guy]

That looks great Matt. It is really coming along well. I am pleased that it is drawing better now that it is starting to dry out. The back cushions should make it much more comfortable to sit there and a covering of some type over the tile should stop any worry about getting too hot to sit there . Great Job !!