Halton Home Inspector wrote:

What ????
I'm sorry to butt in, but there is no need at all to shut off the main power switch to any furnace when changing the filter. You allways do that at the thermostat.
The main shut-off in the basement is only in case of an emergency or if the system needs service. Otherwise, it should always be left ON.
Andy Shaw - 905 876 4761
http://www.haltoninspections.com
Of course either way will work Andy. I use the switch in the basement simply because that's where I usually am when I notice the spare filters and remember it's time to change it.
John Allingham, Professional Engineer
Owner & Certified Home Inspector
Halton-Peel Home Inspection
(416) 254-5869
www.peelhomeinspection.com