No way would I have that stuff cooking inside my house without exceptional ventilation... I don't have that, so I'm a garage man by default. It gets plenty cold here in the northland as well (high tomorrow of 4F/-15C), so I have a couple of Mr. Heater units that I point toward me when I'm working in the sub-freezing temps to take the edge off; I also use a toaster oven to preheat my molds and injector for better shooting. Once I get everything humming, the molds stay at a good temp on their own... the injector may or may not need a little help depending on how fast you're shooting.
(FYI: The garage can get a bit overwhelming without the door/window open, but I don't stay out there for longer than it takes to satisfy the itch; once I'm back in the house, I don't have to smell it anymore and I like it that way.)