Greenhouse heater - 6" Batch box

[wiscojames]

Firebrick burn chamber, 5 minute riser (thanks, Pinhead), bell made of concrete block (4x8x16), ~12 feet of semi-insulated (foil/bubble wrap) chimney outside.

A rectangle of 1/4 inch steel with a circle cutout for the ceiling. (directly under the steel barrel, just a bit smaller diameter.

I'm probably short on mass and ISA, but it heats up nicely after a couple of hours, from top to bottom, and stays warm for a long time. (Sorry, no hard data yet.)

For a door, I opted to make a door using some glass I had on hand.  I had a friend cut and weld two frames (one with support brackets and a handle) to sandwich the glass.  Held together with 4 small stainless bolts. Ceramic fiber gasket on each side of glass.  Freestanding door has some advantages, as well as the obvious disadvantages.  The few times I used it before the door, I was using thin cement board.  No fun not being able to see the fire.

I mortared (with clay) firebricks on top of the barrel because there is a hole on top from a previous project.  About 9" top gap between riser and barrel.  I am considering putting a piece of glass there as well, to allow a view of the flames in the riser.  

In the cold, windy weather that we have had, I have primed the chimney with a hair dryer for a few minutes before and after starting the fire.  Once draft is established, it's done very well - no smoke inside the greenhouse, even in gusty conditions.

I used Roxul foil backed wool boards to protect the wood and poly walls, as well as stacking bricks around the barrel.  Also a layer of cob covering the entire steel plate. 

Still in the process of prettying it up. 

Need to install secondary air before next firing, just a rectangular steel tube on the floor of the firebox, for now.

Can't wait to fire it up for the first time with the new door!

A few pictures:  drive.google.com/drive/folders/1R3um4fg-MWjOpRGF3CBYkM0QFnfGsdwF?usp=sharing

[brco]

sorry,coudnt open pictures

[wiscojames]

Should be fixed now - drive.google.com/drive/folders/1R3um4fg-MWjOpRGF3CBYkM0QFnfGsdwF?usp=sharing

[minervalong]

That looks great!! Just almost what I'm looking for but with a bench for a secondary bell. My planning program crapped out on me so until I get the ooomph for pencil and paper, just gonna have to design in my head. Love the door by the way! Elegant solution.

[wiscojames]

Just as a point of reference, I burned two medium batches (each load consisting of ~4 pieces of 3" diameter wood and 2-3 5" diameter pieces - all my wood is cut short, about 12-14 inches) tonight and the whole bell was pretty well charged with heat. The outdoor temp went from about 10 degrees to 6 degrees over the 2 hour burn. Inside temp went from 36 to 49, which is where it is now, an hour after the fire went out.

Like you, minervalong, I'd like a bench. Next time. If I had been more patient, I may have held out for a different design with a higher firebox. Again, next time. I like what I have, though.

[wiscojames]

I replaced the firebrick splits that I had cobbed on top of the 6" hole in the barrel with a piece of glass on some 1" fiber blanket.

drive.google.com/open?id=0B28osnbq9mRobXFzcWMtMl9lcVFfZWdncHRmT05wOGRMbW53

[wiscojames]

The glass ends up being perfect as a hot plate for a teapot or a cast iron pan, as well as having a peek into the riser. At night, it projects a nice orange glow upwards. Otherwise, a batch box at floor level isn't producing a lot of light.

[wiscojames]

Just burned a full load for the first time earlier tonight and the fire came out of the riser right up to the glass. Wow.

I need to check the temperature rating of that glass again (1400F?). I had a standby solution in event it failed.

I cut back on primary air and was able to slow it down to a less aggressive pace.

I'm guessing that during the average burn, the gases are cooled to, say, 500 degrees after they stream down from the steel barrel into the concrete block body.

As I know these aren't refractory, I wonder what the failure point is for these blocks, and what failure looks like. Crumbling interior surfaces after 20 hours at 500 degrees? Any takers on throwing out some guesses? I suppose a taller and\or larger diameter barrel would reduce temperatures downstream. I might do that to extend its lifespan.

The thing works well, and was relatively cheap and easy. It operates well, and the operator is getting better at operating it, as well.

[matthewwalker]

Once you drive all the water out and break the molecular bond they will start to turn to powder, but I'd be surprised if you got much of that after the barrel there. Possible over time, but I wouldn't worry about it until they start to show crumbling.

[wiscojames]

Thanks, Matt. That's what I was looking for. If it lasts a couple few seasons, I'll be delighted. And ready to reconfigure the thing.

[wiscojames]

Pictures to go with that previous post:

full load: drive.google.com/open?id=0B28osnbq9mRobzRBZkMzZHFkZkVTQkdWZkRkQzFXcFVWWllN

burning full tilt: drive.google.com/open?id=0B28osnbq9mRoZEI5bUEwWXZfTHprLUFQaVdBNU1ZOVdMT1FN

primary bell full of flames: drive.google.com/open?id=0B28osnbq9mRoZEJ3MTJLeWRpNE5JWFZuRkRPWnVnOWpkdkJn

[wiscojames]

And here is the video to accompany, "burning full tilt": drive.google.com/open?id=1Oj9ZrDWjtCPfbN7YFPiGgljzgCRnFAxJ

[n8ivetxn]

Feb 12, 2018 18:27:17 GMT -8 wiscojames said:

Just burned a full load for the first time earlier tonight and the fire came out of the riser right up to the glass. Wow.

I need to check the temperature rating of that glass again (1400F?). I had a standby solution in event it failed.

I cut back on primary air and was able to slow it down to a less aggressive pace.

I'm guessing that during the average burn, the gases are cooled to, say, 500 degrees after they stream down from the steel barrel into the concrete block body.

As I know these aren't refractory, I wonder what the failure point is for these blocks, and what failure looks like. Crumbling interior surfaces after 20 hours at 500 degrees? Any takers on throwing out some guesses? I suppose a taller and\or larger diameter barrel would reduce temperatures downstream. I might do that to extend its lifespan.

The thing works well, and was relatively cheap and easy. It operates well, and the operator is getting better at operating it, as well.

The blocks you're using are the same kind I used last fall on my first build. It held up all winter, also in a greenhouse.... I wasn't able to get a temp reading, but that thing would really kick out the btu's! I did have some issues, but it limped along all winter.... I fired it at least once daily for about 5 months. Sometimes more during January and February.....When I disassembled it in May (currently doing a better re-build!), I saw no evidence of crumbling, nothing was broken.

My biggest issue was the type of mortar I used. It didn't hold up well and I had to plug leaks.... I thought I'd bought something that could tolerate heat, but now I know I misread the label on the bag. This time, with my rebuild, I bought a premixed, 50lb bucket of Super32.

Hope this is helpful! 

[wiscojames]

Thanks for the update on your greenhouse heater - I have only used sand clay mortar and it worked well.

[ronyon]

Very cool!
The use of the concrete blocks has to make this build so much easier.
Im wondering if all concern about destroying the cement could be dismissed by simply adding water back into the environment.
Perhaps you could heat water on top of the barrel, and direct the resulting steam into the bell?