I'm not going to split the heating bill evenly with my roommates
Is there a reason why you do not want to split the bill?
Because my roommates keep the thermostat in our drafty old house higher than I'd like it to be
You need to comply with your original agreement to split the heating bill evenly with your roommates. You are being cheap and unfair and need to pay your fair share or your roommates will take you to small claims court to recover the money.
I don't care, my roommates are just a means to my ends.
If you need them to help pay, you should pay your fair share too. Not splitting the bills properly is going to cause problems with you and your roommates.