i'm going to use a woodstove for heating our barn and greenhouse ... one of those kits made out of a 55 gal steel drum.

neither structure is insulated, so i'm looking to build around the barrel woodstove some type of large thermal mass using concrete or bricks, to store heat during the night. i've read that any concrete used should be a special hi-temp mix or it will breakdown quickly.

i was thinking of just making a 'form' around it, and then just pouring concrete into the form, allowing for openings to throw wood in, clean out ash, have a combustion air source, and of course allow for good exiting of flue gases.

i'd also like to make some 'branches' coming off the stove to help channel the heat into different parts of the greenhouse, wihtout the need for electricity. i know it sounds a little crazy, but i figured there must be some way of 'naturally' directing the heat so there's some uniformity rather than just one big stove in the center.

any suggestions on how to build this thing once the woodstove is made? i know there are some books on building adobe-type stoves, and will take recomendations on those also.

-- lou (lanny1@ix.netcom.com), November 23, 1999

Answers

The problem with the "drum" woodstoves is that they have a large surface area compared to their volume. While quite efficient thermally (large surface area), the gasses from the stove cool quickly once they leave the stove creating a considerable amount of creosote. The problem is worse with the damper closed somewhat.

I own and use a "Sotz" heater from the early 80's. To get around the problem of cold combustion, I have considered putting a 30 gallon drum inside the 55 gallon drum and pouring concrete between the two drums to act as a "thermal barrier." Also, I could then mount the second drum above the first (as you usually see the stove kits shown in the catalogs) and thus have the efficient combustion *and* efficient heat transfer characteristics in one unit.

Of course, one of the most efficient thermal storage mediums is water. Perhaps just putting a bunch of filled black painted drums around the woodstove might do what you want by themselves. Once you get the drums good and hot, they would radiate heat for hours. One design of a "self sufficient solar greenhouse" I was partial to showed filled drums used as supports for the plant flats.

I don't know if Sotz is still in the business of making stove kits, but a dandy accessory they use to sell is a "thermostat" that mounts to the front of the door and controls the stove draft through a "bimetallic" temperature sensing element (it senses the temperature of the door) I have this device and it tends to "even out" the stove output. Amazingly self controlling, pretty much we set the thermostat for the winter and only at the fall and spring to we have to move it much to compensate for warmer weather. It saves about 20 percent on the wood we use. I recommend you get one of these if you can.

The company used to be called Sotz, Inc. My most recent internet yellow page searches at the search engines didn't show anything.

Hope this all helps,

-- Joe (KEITH@neesnet.com), November 23, 1999.

You want high thermal mass?? In Japan, Korea and northern China most houses in the country have the kitchen floor four feet lower than rest of house. The flue from the cookstove (an earthen bank with large pots set in holes) runs under the floor of the house to a chimney on the wall at the end of the house. The floor of the house is thus warmed. In your greenhouse ......put barrel stove in four foot deep hole at one end of greenhouse ....dig trench for the stove pipe/flue to other end of greenhouse. Install flue in trench. Cover with dirt. The entire floor of the greenhouse will be a heat sink. ALSO if you take to the hills ..... in semi-permanent camp put same arrangement .....stove at low point ........flue in trench....... cover flue with dirt. Pitch your tent/lean-to over the covered flue. Floor is heat sink. Mighty smart some of them inscrutable orientals. Some of us scrutible occidentals are smart enough to learn from 'em.

-- Vlad (Strelok60@yahoo.com), November 23, 1999.

If you pour concrete around it, be sure to make some allowance for expansion of the stove within the concrete. Maybe wrap the stove with something that will provide the spacing? Why don't you insulate the structures as much as possible? Any insulation will help, as will sealing areas that could allow drafts. To allow for combustion air to the stove if you seal up the buildings better, run clothes dryer duct material from the outside to close to the stove air intake, so the stove is less likely to use up oxygen in the building for combustion.

-- Jim (jiminwis@yahoo.com), November 23, 1999.