If you are going to pipe fresh air in, do it from outside. Garages are not hooked up to any ventilation systems so during the summer they get extremely hot and then very cool in the winter. You don't want to be sucking in air that is working against keeping your tank at a stable temp. Also, if you have anything in the garage that produces fumes (i.e. gasoline, paint/stains, fertilizers) you don't want to suck those fumes into the house either.