I live in a 1930's era home in a St. Paul, MN suburb. We've been gradually renovating the house which has included new windows, vapor barriers, and bath exhaust fans. The house doesn't have a fresh air intake and I imagine after sealing it up better I'll need to install one, am I correct? The furnace is a high efficiency model with a coaxial exhaust and combustion air pipe, so it has it's own air supply. But the water heater and gas dryer use basement air for combustion, and of course the new bath fans depressurize the house compared to before the remodel (no fans). I know I have a back drafting problem on the water heater since some plastic fittings near the exhaust flue opening have melted. The water heater flue is routed up through the old oil furnace chimney. Is my best course of action a fresh air intake into my utility room (furnace, water heater, and clothes dryer all in same room in basement)? If so, is there a guide on proper sizing and such? If there's a better option, I'd appreciate the advice. Thanks!