Burn coal in a rocket stove?

Rocket Mass Heaters, Rocket Ovens, Cold boxes, Solar collectors, etc..
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Re: Burn coal in a rocket stove?

Postby matt walker » Sat Jan 26, 2013 2:59 am

Geez, my last post is a grammatical nightmare. I'm fortunate to have been given an Ipad for some rocket heater work I did for a friend, and I am really enjoying sitting on the stove's bench with it, but it's not helping my posting quality any. Sorry about that.

Anyway, Mike, I think I am probably well north of you, hold on....

Ok, you are 39.62N and I'm 48.11N. My weather is weird though, I have only a handful of days below freezing, and only a handful of days above 70, due to my proximity to a consistently 50 degree F ocean. Single digits are almost unheard of, maybe once every few years we'll get that cold at night. Here, the biggest problem is light, which is why I haven't bothered with a stove in my greenhouse. I'm on the north side of a 2,000'+ hill, so I get very little light from November to March. Not only that, but it's mild enough here that I can go down to the garden right now and pick cabbage, brussel sprouts, a variety of mustards, enough kale to choke a horse, chard, and some other stuff I discover when I poke around.

Back to the stove. What I meant is that in my experience the mass, if built up at least 6" in every direction around the flue pipe, will take quite a bit of consistent burning to dry completely. Until it does, the stove won't be running at it's full potential. So, due to that, I always encourage people to start drying the mass out asap, and add on to it as it becomes dry. Trying to do a huge mass on the first go can often lead to a difficult first few weeks, if not a month, of difficult performance, as the exhaust is way cold compared to what it will be. One thing that helps a TON, in my opinion, is covering the mass to get the temperature up. Put some blankets over it while you burn and I bet you'll see it's average temperature go up by 100 degrees. In that way you can get warmer morning temps if you go to bed when it's 200*F instead of 100*F.

What I meant by adding on was that if you are waking up to the mass being 50* when it started at 110*, if you doubled it's mass and got it to the same temp, it would be much warmer in the morning. So, I'm not saying to change your exhaust layout, but rather build up in height and width around it with cob/rocks. You will reach a point where your average burn is long enough to heat the whole thing, and it has enough mass to maintain the temp in the hoophouse until you return to burn it again. It will be a balancing act, but looking at your photos I bet you could easily double the mass and still be able to warm it in a reasonable time.

Do cover it, old Goodwill blankets or something will go a long way to bringing your overall temperature up. Then you can play with when you cover/uncover to suit your schedule the best. Oddly enough, I find it better to cover when the stove is warming up the mass, uncover while it's running and up to temp, and then cover again for the last part of the burn and leave it covered when it's out. It seems counterintuitive, and I may be wrong (again), but I find it keeps the mass temp up and therefore the space as well.
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Re: Burn coal in a rocket stove?

Postby matt walker » Sat Jan 26, 2013 2:59 am

Oh, I forgot to say I bet we'd all love to see produce porn. I know I would!
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Re: Burn coal in a rocket stove?

Postby Mikimble » Sat Jan 26, 2013 11:43 pm

Hi Matt,

Are you in Canada or US? I assume you are talking about the Pacific ocean? No offense, but your weather sounds boring. We get all the extremes in WV it seems. 90's in the summers and single digits in the winters.
I'm on the top of a 2000 foot hill too; but built my house facing exactly south. We're on the south side of said hill, so we get a lot of sun year round. I am jealous of your ability to go out into your garden and pick all that stuff. Right now, all I can pick is snow. It's been snowing here off and on for 24 hours. Supposed to go down to 11 tonight, so I've had a fire going all day.
The mass on my heater, the long 22 foot cob/rock pipe was completed around Christmas. I've been burning pretty consistently since then, do you figure it's dry by now? How would I tell?? It's not steaming anymore like it used to when I fired up.

I can only really increase the mass on two sides: top and outside ( the two sides that you see ). The other side butts against the bed, and the bottom is inaccessible. But that would be ok, as I would like to make my beds deeper there anyway. Making the beds on that side deeper would also increase the heater mass too, I guess. But it's just too cold right now to go digging for rocks; plus they're all covered in snow.

About the covering of the mass; is that to dry it or just the way you now run your heater for optimum mass temperature? I have some rigid insulation I could use for that I guess.
Will send in some veggie pics soon; but going snowboarding tomorrow, so it might be a few days...

Mike
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Re: Burn coal in a rocket stove?

Postby Mikimble » Sat Jan 26, 2013 11:45 pm

Hey PA,

You're right about alternating layers of wood and coal; that's what I used to do too. In a rocket heater though, the fire is burning sideways. So, you would have to have your layers running vertically instead of horizontally. I haven't tried it; but that's how I think it would work. See what I mean??

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Re: Burn coal in a rocket stove?

Postby matt walker » Mon Jan 28, 2013 6:36 pm

Mike, hopefully you are slashing a big ol' pow turn right now. I wish I was. I haven't made it to a ski area yet this year, and so far no rideable snow at my place, which is a bummer.

As for telling if it's dry, maybe put a little piece of plastic on a section of the mass while burning the stove and see if it gets condensation from below?

As for covering it, that's how I always run the heater. Without the covering the mass is 100* or so cooler. I'd be inclined to cover with something that breathes, like an old blanket or something. That way you get the temps up but the cob can still transpire moisture if it needs to. Not only that, but it will couple better with the mass.

And yeah, my weather is pretty boring.
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Re: Burn coal in a rocket stove?

Postby Mikimble » Tue Jan 29, 2013 4:06 pm

Hey Matt,

Did get to scarf up a little powder over the weekend. Now it's 65 and sunny. Sorry to hear about your lack of snow. Where exactly are you located, or is that uncool to ask. I always thought there were lots of resorts and snow out west. I've always wanted to go ride the mountains out there. I will try to cover up the bench when it get's cold again and I fire up the heater.

Mike
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Re: Burn coal in a rocket stove?

Postby matt walker » Tue Jan 29, 2013 5:11 pm

Totally cool Mike. I'm on the Olympic peninsula in Washington. Overall we've had snowpack way above normal at all the area resorts, I just haven't made it to one yet this year. I've got a little slope on my property that I love to ride when we do get snow, but that doesn't always happen this close to the water.
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