What is the lowest temperature tarantulas can live in?

[Andrea82]

Of course the best temperatures for them to thrive is about the same as ours, they eat more and are most active (in T terms lol) in those conditions.
I only wanted to know what temperatures they can survive as it can get quite cold in winter nights here and my electricity bill is absurd high already.
At the moment I keep the subadults / adults at around 20-21°C / 70F at night and up to 24°C / 75F daytime. The slings are all in an old tank with thermostat at slightly higher temperatures.

Those temps are fine, even for tropical species in winter.