If your house is set up all electric be sure to get a vented unit, preferably a sealed one with the combustion air pulled in from outside.  Homes made for electric are typically tighter built and better insulated.  And has been said, go small.  Our old farmhouse was drafty enough fresh air was not a concern.  If the wind was from the north the living room was cold.  We put in a free standing unvented gas fireplace and it would never burn more than 5-10 minutes before the thermostat shut it down.