Simple solar heater can be energy efficient

Q. I am on a limited budget, but I want to do my part to cut down on carbon emissions. My kitchen window faces south, so I thought about building a solar heater for it. What is a simple, inexpensive design?

Deb R.

A. Even if the solar heater can warm only one room of your house, it can make a significant difference in your annual use of carbon-based fossil fuel. In addition to reducing greenhouse gases, it will also reduce your utility bills. A simple do-it-yourself solar heater will pay back its material costs and provide a better return than most other investment options.

If you are looking primarily for low initial cost and simplicity, a solar box window heater is an excellent design. With a sunny south-facing window, the output air temperature can easily be above 120 F in the afternoon sun. Depending upon how many old scrap building materials you have around the house and how fancy you want to make it, its cost can be under $100.

As its name indicates, it is just a long box with two chambers, one above another, inside of it and a clear top. The top chamber is painted flat black with optional aluminum baffles to capture more of the sun's heat. It is mounted in a south-facing window with the outdoor end tilted down toward the ground.

Room air is drawn through the window into the lower chamber. It flows down to the end of the chamber near the ground, through a gap between the two chambers and up into the upper chamber. There, it is heated by the sun through the clear top and then it flows back into the room.

This solar heater design uses the thermosiphoning principle to create air flow through it. When air is heated, it expands and becomes less dense. The air heated by the sun in the top chamber is less dense, so it naturally flows up and out in the room. This draws more room air into the bottom chamber.

The basic box can be made from any material. I had some scrap 2-by-4 studs and plywood, so I used those materials. It is very important to insulate the sides and bottom of the box for two reasons. First, insulation reduces the heat loss from the room air flowing through the cool bottom chamber. Second, keeping the upper chamber warmer increase the air flow rate.

The ideal material for the clear top is an old storm window or storm door pane. It will already have a frame on it making it easier to attach and seal to the box. I bought a sheet of clear acrylic plastic and cut it in half. Using wood spacers, I made a double-pane cover for the top.

Drill some weep holes through the inside pane to reduce fogging between the panes.

The solar box window heater can also be used as an exhaust fan for your kitchen. Install a hinged vent panel on the top of the box just outside your window. During summer, block off the heated air outlet into the room and open the vent panel. This draws air from the room similar to when it is heating, but the solar heated air exhausts outdoors through the vent panel.

Q. I have an older sun room attached to my house. The seals in many of the windows are getting foggy. I cannot find any sun room companies to repair them. They only want to install a new sun room. What should I do?

Cyndi H.

A. Over time, the seals in almost any double-pane window will become leaky and this results in fog between the panes. There really is no good way to repair the glass seal other than replace it.

Very few sun room companies make their own glass for their units. Your best bet is to carefully measure the leaky windows. Contact local replacement window companies. They should be able to make replacement panes for you.

• Write to James Dulley c/o the Daily Herald, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.