Jacquie Flint

I like it. I'm able to see things I might never have thought to look for.

Agreed. That's why I was so curious. When I finish my permanent rmh, I plan to experiment with a portable version, but not one as small as this.

This is beautiful - a work of art! It's been three years since you posted. How is it working? What size area is it used to heat? How has the cement held up? How often do you have to burn? How long does it radiate heat? Lots of questions, but this inquiring mind wants to know. Thanks! ~Jacq

The stacked bells would likely be the best option, Satamax. I was going to have a very short bench, but that could very easily be converted to height.

Glenn, thanks for the warning about 4" systems. I'll leave that alone. This will be my first build. Maybe I can use leftover firebricks for mass. Heated area will be 420 sq. ft., which is my kitchen and living room (sparsely furnished - I'm somewhat of a minimalist). The house was built in 1953, stick frame, 8' ceilings, oak tongue & groove flooring, crawl space beneath. The climate is erratic here in the Piedmont area of NC. Last winter we had shirt-sleeve weather followed by sudden snow and ice storms a couple of times. This summer has been more like spring so people are saying that means a cold winter. Who knows? Generally, this is a mild climate with an average of 20-25 degree difference between day and night temps, so a massive heater isn't warranted. Moving off grid is motivated by economics and principle.

Edit: No insulation under floorboards, therefore drafty.

A fine example of excellent German engineering!

That's a great idea, Satamax. I inspected the rest of the bricks (I have 44) and found that only a couple of them have cracks. However, I now want to test the bricks without cracks also.

Would you, or anyone, happen to know if my system size/CSA would be limited by having about 8' of ducting through the thermal mass plus about 7' of vertical exhaust?

I'll do it. Nothing ventured, nothing gained, right? If they're not good for the system, I can use them as the floor of the bench. I really appreciate you.

BTW, I just found this AWESOME thread: https://permies.com/t/30551/rocket-stoves/Fake-fire-brick

Thanks very much for the info, Ken. Would it be worthwhile to do some heavy duty burn tests on the bricks, or should I just buy new ones from a storefront?

Thanks for the input, Ken.

The bricks were outside for over a year, according to the guy I bought them from - and unused. He said he got them from either Lowe's or Home Depot (can't remember) for .60 each, which is what he sold them to me for. The wedge look is because of the angle the photo was taken.

I was planning to make the entire 'J' with this brick, so it would have to go inside the drum. From what I understand, the heat riser can't get too hot on the outside of it or there won't be enough of a temperature differential between it and the drum to cause draft.

I'm thinking maybe either refractory mortar or a perlite/clay slip mortar to fill the gaps and angles (as opposed to a full wrap) might be enough insulation, without increasing the outer dimensions of the heat riser.

I'm also thinking maybe a 4" system would be more appropriate for the size RMH I want to make.

Hi all. I acquired some firebricks for my RMH before a thorough research into building it, so I have some questions about these firebricks. They measure 7 5/8" x 3 5/8" x 3 5/8" - I don't have a scale, but they're extremely heavy. The color is white with the barest hint of pink and there are sparsely scattered specks of what looks like silica. I can't find any reference to this size brick online, even going to mfr sites for every type of firebrick I've come across.

One concern has to do with insulating the heat riser. With these clunky bricks inside a 30-gal drum having an inside diameter of 18 1/4" I'm afraid the gap between the heat riser and drum will be too small if I wrap insulation all the way around. If I knew the rating of these firebricks...

The other issue is I think I want a 6" system, but the closest I can get to that is 6" x 7 5/8" with these bricks. Is a rectangular system doable, or should I make it 7 5/8" square? Which leads to yet another question. I'm going to make a very small RMH with a footprint of about 20" x 48" (there's wiggle room). I think I glommed somewhere that the length of the ducting through the thermal mass is dictated by the system size and vice versa. Does anyone have any thoughts on this?

Thanks from Fayetteville, NC!