The tent is to keep off wind, rain and snow. It won't imsulate well, so you still need to keep warm inside. I second the comments about being very careful about CO gas in a tent. Personally, I would not use any fuel that burns, unless you do the cooking right at the moth of the tent and the gases can exhaust outside.

To stay warm: Buy yourself a very good sleeping bag, and then if you are still having problems with cold - put something warm inside the bag. You can get those heat generation pads from an outdoors store, or boil some water (outside the tent) and put it in an old-fashioned hot water bottle.

the other Pete