Sensible

clear acrylic (Plexiglas) plastic. Use shiny foil duct tape on one edge of the top to function as a hinge.

This simple oven will probably not get hot enough to roast meat or bake bread, but it will be adequate to steam rice and vegetables and heat a cup of tea. Use a covered pot that is painted flat black.

To attain higher temperatures, use plywood to make the boxes, and stuff high-density fiberglass or rock-wool insulation between them.

Make the boxes deep enough to add a slanted shelf. This shelf allows you to tilt the box so the clear top faces the sun more directly without the pot sliding off the shelf or spilling.

To improve efficiency, use two layers of clear acrylic separated by a small edge spacer for the top. This creates an air gap similar to double-pane windows. This slightly reduces the amount of solar energy that gets into the oven, but greatly reduces the amount of heat lost back out through the top.

Also, add reflective side and back panels to increase the effective solar-energy collection area. Cardboard covered with shiny aluminum foil is effective. Don’t use a standard glass mirror. Mirrors reflect visible light, but not heat energy, so little additional heat will be gained.

For some serious solar cooking, select one of the professional solar ovens. I use a hybrid model by Sun BD Corp. that has a built-in electric heating element in case clouds roll in while you are cooking. It includes an adjustable mirrored top and side panels and can cook anything you like. All the various solar-oven designs collapse for easy mobility and storage.

Q. Our central air conditioner seems to be running fine, but there is some liquid leaking out from the bottom on the floor. I think it might be Freon. Is this a dangerous problem?

A. A Freon leak would not appear as a wet spot on the floor.

Also, if Freon is leaking, the working pressures would be incorrect, and the unit would not cool properly. It is probably a clogged drain tube from the pan under the evaporator coils.

Mold can grow in the pan and clog the opening to the tube. Try running a straightened coat hanger or a flexible wire up from the drain tube outlet. This should dislodge the clog.