Passive Solar Heat: Heating that is Clean and Economical

We live in a strawbale house and have a rental unit that is also strawbale. See my other articles on building an alternative house and building with recycled paper for more information. When I engineered the house I Incorporated a solarium on the south side for solar gain in the winter. It was easy to build and could be framed with wood but I used steel pipe. At one point in my life I was sent to trade school to be a certified weldor and the framing for both the house and the solarium are welded steel pipe. Structural steel that can be bolted together could also be used.

The roof is pitched and covered in such a way to take full benefit of the winter sun, when it’s lower in the southern sky, and to block out direct sunlight during the hot summer months. We have a good friend who did a somewhat similar process. He spent hours figuring the angles of the sun and designing overhangs, roof pitches and other factors. I found it much easier to go out and look to see where the sun was and design accordingly. I built the house as I had time, so watching the sun in the winter and summer wasn’t a problem.

The sides are made of fiberglass paneling, like roof paneling, and the vertical steel supports are on three foot centers. I used three foot centers because the windows are three by five. The windows and steel pipe were drilled to an appropriate size and self tapping roofing screws, the metal to metal attaching type with the seal washer, were used to screw the windows to the pipe.

The roof is slightly over seventy percent, north to south, 5/8″ plywood with corrugated metal roofing screwed to the plywood with metal to wood roofing screws with the seal washer. The roof supports are welded steel and the plywood is attached to the steel pipe by drilling and using screws the same as those used for attaching the windows. The rest of the roof is fiberglass paneling to allow for maximum solar gain in the winter. The fiberglass paneling is attached to the pipe with roofing screws that have the rubber type washer and are made for attaching metal to metal. The screws can be purchased at any quality hardware store. I would advise buying a nut driver that can be used in a rechargeable drill. Doing a thousand screws by hand takes too much time and effort. Regular electric plug in drills turn too high a speed and will often twist the screws off. Once a screw is broken in the hole, it’s a major job to remove it. Leaving the hole open poses problems, sealer isn’t as good as a permanent screw. Even the 120V variable speed type drills can be a problem, squeeze the trigger a little too much and pop goes the screw.

There are three double pane windows on the south side and glass doors, with windows that slide up, on the east and west sides. The concrete slab doubles as a thermal mass. Last night it was 23 degrees and by 9:00 Am it was eighty-two degrees in the solarium. The outdoor temperature at 9:00 Am was forty-eight, the wind was blowing and the chill factor was probably in the low forties.

The windows on the south side of the house share a common wall with the north side of the solarium. Once the solarium heats up to eighty-five degrees, or more, we open the windows on the south side of the house and, if the weather permits, a window on the north side. This gives us a flow through that helps heat the entire house.

The solarium is thirty-five feet long by nine wide by ten high. These sizes were used because that’s the way it came out. On days when it’s sunny and warm, it’s possible to open a window in the south wall of the solarium, or a door on the windward side, and pressurize the solarium slightly. This causes a better flow-through in the house. By opening a window on the downwind side in the house, a negative pressure is created and warm air will be sucked through the house.

Our bedroom is on the northeast side and our office/ computer room is on the north. When conditions are right, we can open the windows to the solarium and those in the bedroom or office, and heat without heaters of any kind. We start our seedlings in the solarium and that gives us a jump-start on the growing season. The solarium has been a time, energy and financial investment that has paid us back many times,and in many ways.

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