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8" Rocket Masonry Heater - Quick Build for Greenhouses

Sandy Mathieu
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Here is another "Bell" masonry heater. All the heat is put into thermal mass for slow release. It is a similar design as the "Castle Builds" but uses Barrels. The advantage of this build is that it is quickly assembled and disassembled for seasonal or temporary usage. It is also cheap to build and provides long lasting heat with just a few hours of firing. Check out the data logs!

Here are links


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Dragon Heater 8" Derrick
Steve Edwards
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I like this design and would like to try building something with a bell next (something like this or the 4" Castle build) - so a few questions if I may...

1) Approx how many fire bricks were needed in this build and could I use cheaper reclaimed house brick (I'm in the UK) for the lower half or 3/4 of the heat storage bell?

2) What is the white gasket being used between the drums - ceramic fibre?

3) Does the foot of the heat storage bell need any insulation where it contacts the floor or are the lowest bricks & exit air temp low enough just to foot it directly onto something like a concrete slab?

4) Those barrel caps are a cast refractory material right? If so, what material did you use and how robust is it to repeated heat stress? I'm new to refractory materials (well, other than clay in cob ) and I guess I'm worried about what might happen if either of the caps were to fail and this were in an indoor situation; are there any mitigation steps that might be taken with an indoor installation?

Many thanks in advance!
Sandy Mathieu
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How many bricks depends on if you have 3" or 2.5" thick. We had 3" and it takes in the 160-175 range.

All the gaskets, and exhaust collars are provided in the kit along with dimensions for all the cuts.

The lower temperature are very cool less than 170F. Slab or cement block will work.

The barrel caps are 3000F heavy cast refractory, that are reinforced.
Not looking good. I think this might be the end. Wait! Is that a tiny ad?
Rocket Mass Heater Plans: Annex 6
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