I also used the Kitfox optional heater kit with two 12v PC fans. I wired them up (as shown in the kit) so a SPDT switch either runs one fan or both fans. Very simple and after using it thru two winters I find that this "two speed" control is very satisfactory; no need for variable control. I also do not have any shut-off valve in the heater coolant line and find that even on a hot summer day (98 F) with both fans OFF there is no appreciable unwanted heat coming into the cockpit. I like the KISS principle.