While looking for a fan and controller, I came across Solar Air Systems' computer chip fan controller that comes equipped with a thermocouple that ramps the fan up when sun is at full strength and ramps down or shuts off completely as the sun's intensity decreases -say if a cloud passes. What this does is; it keeps the fan at adequate rpm to keep positive pressure flowing into the unit which also ensures the fan motor does not burn out prematurely. What's also nice about these fan controllers is they fit a nice wall mount that has a filter, so your installation looks professional.
Hope this helps, Eric
Fan controllers and wall mount kits can be found here: http://www.solarairsystems.com/shop/def ... 224317blue
rookie35 wrote:All three of the air heaters install simular to a window air conditioner unit and have bathroom exhaust blowers attached to the inside and wired to a liitle trip thermometer. When the air heats up to like 110 f. it will start to blow and when it cools to like 70 f it shuts off. I used them over this past winter but, the weather was so warm I think they kicked on only six times and every time it was like in the 30's. So I don't know how well they work when it is bitter cold yet. But my furnace did not kick on when these were working. It does also seem that the one least expensive to build works the best as in temperature but as far as cfm's they are probably different as the exhaust outlets vary in size.