Like the thought that cranking the thermostat all the way up or down cools or heats a home quicker, the belief that closing some family ports increases overall HVAC performance and efficiency is a busted myth. In reality, it usually has the opposite effect. In today’s energy-efficient residences, air flow is balanced to preserve neutral air pressure in each room. When some ports are closed, that delicate balance hints, energy consumption increases and household relaxation declines.
Increased Duct Leakage
Even with all ports open, the Department of Energy estimates the typical house loses up to 20 percent of heated and cooled air through leaky ducts. But that percentage climbs even higher if some supply ports are closed. Air pressure inside supply ducts increases in proportion to the number of ports closed and shoves still greater quantities of conditioned air out of existing leaks. Your furnace or A/C runs more “on” cycles to compensate for your reduction, boosting operating expenses.
Although the supply enroll into your room is closed, the return enroll from the room (which cannot be closed) proceeds pulling air into the furnace or A/C. Room air pressure changes out of neutral to negative. A closed, depressurized room always sucks unconditioned outside air in through small gaps and cracks which exist in almost any structure. Room temperature gets cold or warm and transfers to adjoining rooms by conduction through walls, offsetting the air conditioner or furnace as well as increasing energy consumption.