Masonry Heater for my Yurt

[hierony]

So winter is coming. I've been

heating

with electricity & a propane space heater, but that gets expensive. The propane isn't vented, which is not great (I've a CO monitor though, & have measured CO with a Fluke meter--no carbon monoxide produced; don't want to run it overnight though). Wood is readily available in my area, very cheap if you do all the work & not too expensive if you only do some of the work (getting logs out of woods, cutting into rounds, quartering, stacking, etc), and is renewable & carbon neutral.

Because yurts aren't terribly well insulated or air-tight & have little thermal mass, I don't think standard wood stoves are a good match for

heating

a yurt. They'll easily heat the yurt when running, but things will get cold pretty fast when you aren't burning anymore. From the sounds of other's experience, it's hit or miss whether you can get your stove to put out enough heat overnight without stoking it halfway through. I've already noticed with the propane heater that though it increases the air temp quickly, all the mass takes a while to warm up (ie, the bed).

So I decided to go with a masonry heater. It has a small footprint (~30x30 inches), should burn very clean & efficiently, will heat continuously so there won't be cold/hot cycles & all the yurt mass will be warm (not just the air). Plus it won't present a burn hazard for people or pets. Cost is around $1k ($200 design fee, $350 firebrick/facing bricks, ~$300 door/ports/refractory cement/misc materials, plus chimney).

I have a strawbale platform & the heater will be heavy, so I had to do something a little different for the foundation under the heater in the middle of the yurt. I didn't put straw bales there. Instead, a layer of leveling sand, cinder blocks to distribute the load & match the wood platform level, a sheet of steel to distribute contact point loads, then a reinforced lightweight-aggregate concrete (perlite & expanded shale), then 1/2" cement board. The cinderblocks can carry quite the load, & everything else will do great in compression & is _not_ burnable.

[hierony]

I've some photos of the process so far: Yurt Forum - A Yurt Community - hierony's Album: Masonry Heater

[Bob Rowlands]

I'm very much looking forward to future updates on the build and use of this heater. Thanks for starting this thread.

[hierony]

I'm building slowly, and not as neatly as I should--the little masonry experience I have was from 15 years ago...



I got the firebox mostly done the other evening, but I'm starting to run low on refractory mortar. Note the slits in the walls--this if for air intake (comes from underneath, then between the inner & outer core). This is the Austrian Eco Firebox design--one of the cleanest burning. Coupled with a heat exchange bell on top, it has a very small footprint compared to contraflow/finnish designs. The white stuff is ceramic fiber/wool/paper--it functions as an expansion joint. The firebox bricks will get really hot (1200-2000 F?), expand a little outwards & upwards--if they were attached to the outer core walls (relatively cool), the joints/bricks would break.

[Bob Rowlands]

Cool! Nice looking khana as well.

[hierony]

Got the upper half done finally!


I just need to get another masonry bit for my jig saw to finish cutting the stove pipe hole:


Next I will need to put up the facing (cement bricks held 1/4" from the core), but that should be a lot less complicated.

To dry out the heater core, I've a little electric space heater running almost all day in the firebox. Should get things nice & dry by the time I actually have everything done & setup (facing; firebox, air intake, & cleanout ports; chimney).

[hierony]

I forgot some of the other photos that I uploaded but didn't link:




Firebox done.


Vermiculite baffle on top of the firebox.


Cast refractory tile for spanning the firebox.


Tile installed.

[Jafo]

Do you have an approximate weight yet on this?

[hierony]

Well masonry heaters generally aren't weighed per se, so you have to take any weight estimates with a grain of salt (or two). I'll move it (& the yurt again) eventually, so I may drop by a truck weigh station :P The heater sits on its own foundation & not my strawbale platform--it would have been near the bearing capacity of the straw, plus straw is combustible...

Initial estimates put it at 1500-2000 lbs. I used ~180 firebricks (7 lbs each), plus ~70 lbs refractory mortar; there's also the 45 lbs steel sheet, ~150 lb lightweight concrete slab, & 10 lbs(?) backerboard. There's a 2" slab of perlcrete + 2" of mortar on top of the heater core to seal it off once I get the facing done. My facing brick estimate seems to be off, so there will be a lot of weight there too, plus any plaster system I put on it. The whole heater will likely weigh more than the yurt & platform by the end of it!

[Jafo]

Wow. Glad you put it on its own foundation lol. That is going to be a heavy sucker.