Garage Grow. How can I insulate heat?

Ok so I plan on doing a garage grow in a grow box. My garage isnt exactly air tight, so it gets very cold in there especially in October-December in New York. Anyway I want to be able to make an airtight grow box that I can grow in and I wanna be able to keep at a good temperature for the plant. How would one do this? And I also need to be able to have a fan going on in there to blow air elsewhere to avoid smell. Thanks.

I spent the last month preparing for the winter. Besides wall insulation I used 1 x 3 and made a 4 x 8 x 6foot high Reflectix Insulated room- which I stuck my tents in. I then took one tent down and left it open air- with one tent left inside for 12/12. While last night was 35 in NY!!! my room was able to stay low 60s. Im going to do more to retain more heat tonight by some small modifications. Use the air to your advantage... cool air coming in is a great way to cool the air in the tent / room....however- careful cuz you are sucking 30-40 degree air and not pushing air conditioner air at 65-68

Lights on (if you're using HID) should be no problem keeping it warm, especially since you're keeping it a smaller scale "box". Just run a thermostat switch at around 70-75 degrees on your exhaust and have a passive intake. Now the dark cycle might be tricky, I would say put a space heater of some sort in the box on a timer and have a lower thermo setting for the dark cycle, to keep it at least around 50-60 degrees. And insulate that thing GOOD. For smell mount a carbon filter before your exhaust fan and have a one way vent on your passive intake.