When it comes to controlling heat (either to keep your home cool or warm) leaks in your home and ventilation system are the enemy. Of course, external cracks and leaks in windows, doors, siding, and your attic are all avenues of heat transfer that will make keeping your home comfortable more expensive, as it forces your central unit to work harder to keep temperatures even. Even worse, leaky seams or damage to the ductwork in your forced air system are just as bad. These leaks, while you may never see them, send climate controlled air into spaces where it isn’t needed. Wall spaces and attics don’t need to be climate controlled and even a small leak in your ductwork means energy lost, a cost that comes out each month your utility bill comes due.
Two things lead to leaks in your HVAC system: backpressure and age. While there isn’t much you can do about age except get regular inspections and maintenance, you can prevent backpressure from building up in your ductwork.
Backpressure occurs in the ducts whenever there’s a blockage. Whether that blockage is caused by a dirty filter, dirty air ducts, a blocked vent, or simply a closed vent the effect is the same: a strained blower fan. You see, most HVAC units have a single-speed blower fan as part of the forced-air unit. It moves air through the system at the same rate. When a blockage occurs, either because it can’t draw air in through a filter or can’t push air out due to a closed vent, pressure builds up in the system. While this causes a higher than normal energy cost for the system, it also forces the air inside to seek other avenues of escape. Weak seems or joints in the ductwork breach, allowing air to leak out. Existing seams may even widen to leak more air.
This is why it’s a bad idea to close air vents in your home. The ductwork has been sized to your HVAC unit appropriately, and it won’t cool more efficiently just because you closed off a room and sealed a vent. In fact, it’s likely to cost you more over time as your unit ages faster and requires repairs more often.