Rocket mass heater outside air supply

[matt walker]

Well, I've been playing in the snow the last few days, and it's finally raining, so it's time to put my head back into my projects. As per my other RMH thread, I'm working on designing a system for my house, and my original plan includes a fresh air supply to the firebox from outside. I've read some recent posting around the web on this idea, and would love to see some more discussion on this concept.

I haven't heard any significant negatives, other than safety concerns, which are easily nullified with good design. The advantages I can see:
1. The warm air stays inside the house
2. The ability to close off the firebox from the main house to eliminate smoke back. MAJOR BENEFIT in my opinion.
3. Better control over airflow.
4. The ability to preheat the incoming air via intake design. i.e. routed close to warm exhaust.

Disadvantages:
1. I honestly can't think of any, other than a little added difficulty in the design/install.


I've got some ideas I'll expand upon, but does anyone have any input, something I'm missing, etc?

[eeldip]

do you have a crawlspace or a basement?

[matt walker]

Yep, basement under main house, crawl space under master bedroom.

*thinks*

Ohhhh, I think maybe I see where you are going with this. Damn, smart.

Okay, why?

[pa_friendly_guy]

To use an outside air source you will have to make sure the design of the stove still draws. The Rocket sucks the air down, through the burn hole and up the tube. Is there any chance that your air source could cause a chimney effect and suck the burn and smoke the wrong way? I have seen a video on you tube where a couple heats a yert with a rocket stove. They changed the fire box to a sideways burn. They had metal plates that they covered their longer fire box with to keep the Rocket sucking. They did not seem to have any problems. Heating with outside air always makes sense because you are not loosing the heated air from your home. My only thought is the draw that the Rocket has and how will it be effected, if at all. I do not really know Matt. Making a smaller test unit might give you an idea. Having the outside air come in near the top of the fire box might be the same as drawing the air down from the top. Your air intake would have to be as big as your up right burn tube I would think.

[matt walker]

Thanks for the thoughts Guy. I saw the yurt heater as well, that's a neat set up.

What I have read of people's concerns regarding fresh air supply seem easily mitigated with a simple manual damper on the fresh air, and an adjustable vent on the feed tube cover.

To deal with smoke back on opening the lid, you would do what you do with a box stove. Get the air flowing the way you want it before you open the lid. In other words, close the fresh air and open the lid's vent.

With the fresh air closed, it would function as a regular stove, but one you could put the lid on. My house has terrible insulation and is drafty. Single pane aluminum frame windows with the seals all loose, etc. I would love to fix the house first, but that's not possible without a lot of monetary investment. When it's really cold out, if the box stove is roaring, I can feel cold air coming through the gaps around the windows and the floor and just about everywhere. I'd like to be able to draw from either inside or out depending on if I wanted to keep the air in my house or change it out.

[pa_friendly_guy]

How much wood are you burning a winter now Matt? My next door neighbor uses between 5 and 6 cords a year to heat his place. He heats 100% with wood unless he is away and then the oil burner kicks on. I burn some wood to suppliment my heat bill but have stopped burning wood as a primary heat source. I have alot of wood here on the property I am to the point I don't want to work that hard anymore. I used an old Rightway wood stove for years, it is a good heating stove, but not a pretty stove. It had a down draft flow with a 2nd burn area that ran along the side of the firebox that would burn the smoke if you burned the unit hot. They were the only wood stove at the time that was UL rated for safety. They have been out of business low these many years now, I guess the UL rating didn't mean much. It has a grate so I can burn wood or coal, 27" fire box, fire brick lined, bi metal thermostate and it will burn all night . If you find a used one I would recommend buying it, they work well as a rediant wood burning stove, or you can have a metal plenum made and add a blower. I used mine just as a radiant heater.

[matt walker]

That sounds like a neat stove, I'll keep my eyes open for one. I'm currently burning probably in the neighborhood of 7+ cords a year. I have a big box stove, of old design so it's fairly inefficient. I, too, am just plain tired of working that hard to have heat. It's a good month of my life every year, between felling and bucking and getting the wood to the house, splitting and stacking. For the last two years it's all come from the property, but I don't think this level is sustainable. I have a ton of coppiced maples here that produce an incredible amount of 2"-4" diameter material each year. Alder as well is just an incredibly fast grower here, I bet it grows 8' a year or so. The rocket mass heater is very attractive to me mostly because of this abundance of perfect fuel for it. Small, smooth, quickly drying, round, straight material. I picture myself letting the chain saws gather dust and leisurely gathering my year's wood supply in a delightful June weekend with a pair of loppers. Lol. I'm sure I'm dreaming, but you gotta let a guy dream!

[pa_friendly_guy]

I agree that dreams are a Good Thing Matt. We all need dreams. The one video I have seem said that this one fellow went from burning 4 cords a year to heat his cabin down to just 1/2 a cord with the Rocket stove. That seemed to be almost unbelievable to me, but he said it befor God and everyone, so maybe its the truth. Only one way to find out, scrap that old metal woodburner and put in your rocket stove. The proof is in the pudding, or something like that. Heating with your rocket stove will tell the tale.

[matt walker]

That's exactly what I keep thinking. It's hard to believe it could make that much difference, but what if it does? I'd rather find out now rather than 10 years and 70 cords of wood later!

[Lollykoko]

My tentative house plans include a rocket stove (one per room) venting through the mass of each interior wall. I figure that with 15 acres (or more) of woodland, I've got plenty of twigs and small limbs that can be utilized for fuel. Passive solar design is configured to allow heated air movement under the floor, but adding "zone heating" will be a plus, I think.