Q) We have recently upgraded to a gas furnace, the intake air for the furnace is brought in from the outside. Are the old return air vents still required?
A) The fresh air vents are still required to bring the make up into the furnace. If your new furnace is a high efficiency model with a variable speed and DC Motor, it should be running 24 hours a day, 7 days a week so it circulates the air properly through your home. I always suggest having a Hoyme Damper installed on the fresh air furnace duct. When the thermostat calls for heat, the damper opens. When the furnace goes off, it closes to prevent the entry of unnecessary cold air.