I agree that heating the tent is not that important, and proper apparel is. Light weight synthetics and layering will keep you comfortable while awake & for sleepy time a good sleeping bag. Keep some base layers on when you get into your bag. Tent camping for more than forty years, regularly, and I've never heated a tent using methods that others have shared here along with what I mentioned. There have been nights when I got into the sleeping bag fully dressed along with hat, hood, and gloves, but was very comfortable (I took my boots off) and still consider heat in a tent a waste. It's just something more to carry with very little payoff. But then I don't think standing in a tent is important either. Had two big tents with rooms during the years that the grandkids camped with us, and gave the tents to them when they wanted to camp with friends when they got older. I prefer a tent that would be useful on a mountain top in howling wind.