[BGCarrera32]

A lot of houses have an air make-up / fresh air supply duct that runs into the room that has the heater. I have a hot water boiler system and there is a 6" insulated flexible duct line that punches through the basement wall and sits a few feet from the boiler. The outside opening for the duct has what looks like a larger version of a clothes dryer vent.

You want to suck in your make-up air through a dedicated supply like that and obviosly not through all the windows, outlets, etc. Because the supply duct is insulated, you don't loose all that much heat.