They also suggested a 75 watt for the same cage when I contacted them. I'm in the SF Bay area, and I don't have AC, so my home never gets really cold. But if I was on the fence, i'd get the larger one. If it's on a thermostat, then what's the harm... the extra size/heat may not be needed, but if it is, you'll have it. No harm if having one that's more then what you need if you have it on a thermostat anyway.