electric fan, wiring check, on/off/on, therm

You won't need a "heavy duty" switch you're only switching relay coils max draw, 3 amps. What's the on rush draw (switching on current draw) of each fan, add about 5 amps to each, that becomes your fuse and relay rating, either one fuse X twice that rating as per the diagram above or two feed lines and fuses, one for each relay, IMO safer. P.S. From your questions here, I would suggest you follow that diagram slavishly.

. I had the fans wired up before with relays but I did not have an over ride switch to them. Thank you so much for you input!Sc300 - 2jzgte

The override switch should switch the relay(s), not the fan power. It just needs a few diodes (IN4004 etc) and a low-power switch.