Rocket Mass Heater for my home

[matt walker]

Thanks for the encouragement Guy! Ok, that was no big deal at all. I've said it before, but these things are easier to remove than a wood stove. At least I can move them in pieces by myself.

Ready for rebuilding!

[matt walker]

Ugh, the hardest part about this whole thing is I have to run to Home Depot. Yuck.

[wileythenord]

So you are putting a half barrel in the cob there as a heat exchanger? What led you to this epiphany? Just wondering what the advantages to the second barrel would be.

[DrewInToledo]

Don't let him fool you Wiley, he's incorporating a whisky still.

[ByronC]

Excellent batch-box retro there Matt. After going through the heating season you'll be all set to do a pros/cons comparison between the 8" J and 6" batch. Did you end up raising the barrel a bit to increase the riser top gap?

That burn chamber top window is a really cool feature. Nice!

[matt walker]

Wiley, I've been using half barrels instead of flue pipe for a few years now. Not always, just another tool in the kit. They are free, can be built quickly, can have high mass or low mass coverings depending on the needs of the system, and form a durable arch form for the cob mass. Here's a video I made a few years ago....



I had the epiphany when I was trying to make thin, low mass benches for outdoor use. I was seeking quick response for heated outdoor seating, and all weather durability that didn't require the cob to maintain much structural strength. Since then, I've realized they have many, many applications. One of the best things I've discovered about them is they can function like bells, so they can be used to form a blind bench(dead end), and also used to eliminate flue pipe elbows as they can form a plenum.

Thanks Byron! I'm stoked to see how it goes, I've already been enjoying splitting wood into larger chunks. I didn't raise the barrel, I really don't have room as I'm pretty close to the ceiling as it is. So far, it's been running just fine. We shall see. Yeah, the top window is awesome for sure. That was a great thing to come out of the Montana gathering.

Here's where it sits this morning. That's not quite the final layout, I think I'm going add a bit more half barrel and kick the front flue run out a bit, but I should have it burning and starting to dry out this evening if I get off this computer. Not sure how I'll finish it yet, maybe just plaster?

[hpmer]

Are you going to have a second flue at the end of the barrel run? I notice what looks like a hole sized for a flue.

I thought from an earlier description that you were going to just do half barrels all the way down and just have it as one big bell, but that's not what it looks like you've done.

[matt walker]

I thought that's what I was gonna do, but it's changed. Might change again before the day ends.

That hole was an exhaust in another build, I repo'd that barrel from my shop system! I think I'll leave it as a clean out.

[mannytheseacow]

Looking good there, Matt. Yep, it's at a point anymore where remodeling these things is like an easy afternoon...

So I remember at some point you were talking about how finicky these batch boxes are. What's your experience with this new one so far? I'm forever frustrated with J tubes and the smoke back/flame creep. I was really looking forward to an 8" to burn bigger wood and so far bigger wood just means more creep and smoke. I'm pretty envious if you are burning bigger stuff. I might extend my feed to 2 1/2 feet deep and mount a door to the top.

[matt walker]

By finicky I meant that they just need the whole system to be dialed or they don't burn cleanly. I think Js are more forgiving of the back end, but I also think your experience is indicative of problems downstream. My J pretty much never crept or smoked, and I often put sticks as long as the barrel was high in there. I'm not sure if it's your fuel, or restriction from your chimney mismatch, but that's not right my friend. At any rate, so far so good, but I only ran about a half dozen loads through it before tearing into again this week. I'm a little concerned that adding so much more run is going to put it over the edge, but we will see.

You have a 6" chimney, so you might be better served trying to get more btu's with a batch than the mismatched J you have now. I am only just kinda wrapping my head around it now, but I suspect that your smaller chimney means slower intake velocity at the feed which means you are more prone to creep. Just speculating, but for sure you shouldn't be struggling like that.