Posts Tagged ‘heater’

compost kotatsu

The other day I was talking with my friend Linda Leigh on the phone. Linda is a worm farmer and was formerly a Biospherian. She told me about an experiment she’d been doing with a compost of coffee grounds and sawdust–only those two things. She said the compost was 138 degrees inside.

Hmmm, I thought. I have been trying to economize, partly just to do the right thing, and partly because I’d like to attend the Fourth Advanced International Colloquium on Building the Scientific Mind to be held at the Sustainability Institute in South Africa in March. In order to go, I have to really scrimp and save. So, I haven’t turned on any heat in my house. I built the windowbox heater, and now talking with Linda gave me another idea.

When I lived in Japan, I became familiar with an item of furniture that is common in Japanese homes called a kotatsu. Most Japanese homes that I experienced did not have central heating. Instead, people used space heaters (often kerosene) and the ingenious kotatsu. The kotatsu is a low table with a heating element attached underneath the tabletop. The table is covered with a quilt that reaches to the floor on all sides, and then covered with another tabletop. People sit around the table on cushions with their legs and feet in the warmth under the table.

Since a compost of coffee grounds and sawdust is bound to smell good (or, at the very least, not smell bad) as it heats up, I thought: Why not build such a compost bin inside the house? When it gets cold, I could siphon off some of the heat.

But I couldn’t build a large compost bin inside the house! Where would I put it? (My house is rather small.) And I certainly couldn’t build one large enough to heat my entire main room.

But I did have an old round tub outside, and I did have an old umbrella table–without the umbrella, but with a solid wood tabletop. It seemed to me that a small compost bin, if it did successfully heat up, might generate enough heat to take the chill off underneath the table.

Hmmmm. Why not give it a try?

Linda came over and helped me build the compost kotatsu.

We put the tub underneath the table and then built a bin of 1/2″ poultry netting.

table with tub underneath and poultry wire bin

Then we lined the bin with burlap.

bin lined with burlap


For the compost, we used free coffee grounds collected by ourselves & friends, from coffeeshops and our own kitchens. Linda got free sawdust from her neighbor who does woodworking. Linda also donated some starter compost from her own bin.

compost ingredients


We added enough water to make it the right consistency.

just right!


Then we filled the bin.

the filled compost bin


Here’s how the assembled compost kotatsu looks,

from underneath . . .

compost kotatsu--side view


and with the table assembled . . .

assembled compost kotatsu


When it gets cold, I’ll put a longer tablecloth on the table to trap the heat.

Within three days the interior had reached 115 degrees. It has been rather warm here, so I haven’t needed to siphon off any heat yet. When I do, I plan to use a simple tube inserted into the compost bin at an angle to perform the heat transfer–an idea similar to that of the windowbox heater. Then I’ll have to observe whether that causes the compost to cool off too much or not.

The best case scenario: free heat + free compost for the garden

The worst case scenario: free compost for the garden

What’s not to like about an experiment like that?


Read Full Post »

Back in the 1980’s a friend built me one of these heaters from plans in the Mother Earth News. At the time, I lived in northern Idaho in a trailer. The heater worked so well that sometimes I had to open the door to cool the place off(!)

I’m no carpenter, but I built a simplified version of the heater for my house this year. It cost me $28 for supplies, and friends donated scrap lumber to help me out. Here’s what it looks like:

windowbox heater view 1


windowbox heater side view

Next year I plan to make it longer and to set it at a steeper angle for greater efficiency.

Read Full Post »