I use a BIG tent, and can warm it up to tolerable levels in sub-freezing weather with a couple of propane lanterns. A small Mr Buddy gets it like home.
I am not out there to be home. I am out there to be close to the hunting, close to the woods. It will get cold in the tent at night, but generally the water bottles don't freeze in there. I turn on the heater in the morning, get out, get dressed and turn it off. Turn it on at dark, peel down and get in the bag, turn it off. Managing ventilation is both for safety and for moisture control in the tent. You give off a lot of moisture as you live and breathe, and the warm/cold sides of the tent make for condensation.
A smaller tent heats up well with just a lantern. Just be sure to budget air for the both of you, and don't expect to be able to stretch out in your skivvies like you were in your living room in front of the TV. Unless your skivvies are long sleeved and long pantsed wool and Thermax. :D
Killdeer