Fiance won't let me turn on the heat to the house

Part of the reason we are together is because of his frugality. I admire that in a person. But, over the past two weeks it has gotten cold. A week ago, the house was maintaining 64F. Now, it is 59F indoors, and the outdoor temperatures are not forecasted to go above 60F for over a week from now. Meanwhile, our first freeze is tonight, 31F.

I need some way to persuade him to turn on the heat. He says he will not turn it on until December. I don't know how that is possible considering that our climate averages nights below 40F and days below 60F starting in November.

Is this not extreme? There has to be some way that this causes more expenses in the long run than just paying the gas bill. We are not poor. We can easily afford it.