There are a few variations on this design, depending on the materials you have available and the type of room you will be heating.

FAN AND VOLTAGE

For the fan, you need to find a small, quiet unit that is capable of delivering at least 100 CFM. If you can find one of these that uses 110 VAC, then you don’t need anything else. Most small fans of this type are 12 VDC, which means that you need a converter from 110 VAC to 12 VDC. These converters are readily available from junk or surplus electronics, and are commonly referred to as “wall warts.” The converter should output at least 12 volts DC, and double the amps your fan is rated for. This gives enough room for the fan’s startup surge.

SIZE OF PLASTIC

The first problem you may encounter is the size of your transparent, corrugated plastic. If you can find a 4 feet sheet, so much the better, as that will match the size that the insulation comes in. However, if you can only find a 3 feet wide piece, don’t worry. You can still use this design, but you will have to cut your insulation down to fit it, and then adjust the metal channel walls, so that they too match the new size.

HEIGHT OF THE ROOM

The next issue is the inside height of your room. You will have two holes through your south facing wall, one at the top and one at the bottom. Air will be drawn from the bottom hole into the bottom of the heating unit outside. This is because it will take less energy to heat the air from inside the house than from outside, as it will already be warmer than the external temperature. The air that has been heated by the unit will then blow down into the room from the top hole. The problem with this is that, in order to make the most out of your heater, you will want the distance between the outside edges of the two holes to be about 8 feet (a little less is OK).

If your room is eight feet tall, construction of the unit will be easier, cheaper and more efficient. Easier, because you will be able to cut a hole through the bottom and top of the heater’s backing (insulation), instead of having to go out through the sides of the heater’s wall, which is more complicated. Cheaper, because you will need less 4” dryer vent, as it will be going straight through the house’s wall, instead of having to curve to the side before going inside. More efficient, because the temperature inside the unit will match the air coming into the room, whereas if you have to go to the side, you will lose a little heat through the extra dryer vent. You can compensate for this by painting the exposed vent black, or, even better, wrap it with insulation.

During the course of this article, we will be mostly describing how to attach this unit to a smaller room. For a start, it is probably more common to have rooms that are less than eight feet tall. Secondly, it is more complicated, and therefore requires a little more explanation. However, wherever the instructions differ for a tall room, we will add notes in bold.