My post was meant as a joke, really.
In northern states in the winter, you have a thermostat and the heat is on pretty much all winter. Its not like AC where you can do without it. When it's below freezing for weeks at a time, you don't have the option of NOT having the heat on. If the heat is off and the house gets enough below freezing for long enough, you'll have a lot more problems like broken water pipes.
Set the thermostat to 68 or so and the tarantulas will be fine.
I live in Newburgh NY in the hudson valley, and in winter I use an oil heater for the T room, set on medium. Mine do fine, even tho the room temp can drop a little cold some nites. I haven't lost any to cold. No way I can afford to have it warm throughout the trailer here, I only use the thermostat to barely keep the pipes from freezing, and otherwise I only have heat in the T room and wherever I am.
I live in Iowa and I keep my apartment around 60* in winter. It's enough to give the spiders a cooling period (for breeding purposes) since my apartment is around 75*-80* consistantly in the summer. Don't worry about them unless you anticipate waking up with frost on your sheets.
my room gets cold and i just keep a little space heater in here and that seems to do the trick.
i've mentioned this before, but i lost power due to an icestorm in my room and it was near freezing in here for 5 days or so. i had about 10 T's at the time and didn't lose a single one, including some warm climate t's. they're tougher than you think. temps don't really need to be spot on ime. my room mates keep the apt too damn cold about all the time and i really haven't had any problems due to it.
You have to remember that a lot of these spiders live in deep burrows in the wild where it's signifficantly cooler than the surface.
Plus even in a lot of tropical periods, there's a 'winter' where the temps drop to the sixties and fifties.
This cooling period kind of cues them in on the season and many won't build eggsacks out of the proper season. A cooling period dramatically increases your chances of getting an eggsack.
In short, a temporary drop in temperatures isn't really all that harmful as long as the drop is within reason. If your apartment stays in the low sixties to high fifties, I wouldn't worry. If you're expecting anything less than 55* for an extended period of time, I'd be worried.