Ian, FWIW I wouldn't trust a snap switch for fan duty. I know the advert says it will "drive the most chunky fans available." however fan duty is really tough on switch/relay contacts. Anything that pulls lots of current, and cycles on/off, I'd wire through a quality relay.
I have a 16" SPAL fan in another hotrod, and it pulls 22 amps continuously, but around 60 amps for a half second or so when the motor starts. That 60 amp peak has wiped out a number of components in this circuit, including two 30/40 amp Bosch relays, two 40a automotive fuse holders, several connectors, and other misc. items. I now have this circuit wired with a 40 ampere large bodied glass fuse, #10 AWG (or about 4-5mm2 European size) automotive stereo power cable, and a 75 amp Bosch relay, and it's been running OK for two years.
So for fan circuits, I'd take the continuous current rating of the motor, multiply by 3 and size the relays or switches accordingly.