The supply vents in your home most likely have dampers on them. Should you close them, even just a little bit to adjust the airflow in your home? If you live in a two-story home, you might be tempted to adjust them when it is either very hot or very cold. You may partially or completely close the ones downstairs when it’s hot outside so the rooms on top, that are warmer will get more attention from the air conditioner. When it’s cold outside, you do the reverse. Closing the dampers upstairs should reduce the amount of air that’s going upstairs and keep more warm air in the colder rooms below. Now that all seems to make sense, right? But it may not be that simple.

HVAC Static Pressure

The HVAC system in your home most likely has a lot of static pressure. Your HVAC system has a large blower fan that pulls air from return grilles. It then blows the same air, that is now conditioned through supply ducts and then through the supply registers. That means a lot of air traveling through all the ductwork in your home. When the air encounters resistance there will be static pressure. Some resistance is good. Without it, there would be very little airflow and the air wouldn’t circulate very well throughout your home. In situations where there is too much static pressure there will be excessive resistance for the air to encounter. This will have the system trying to move large amounts of air through a restricted pathway. Too much static pressure can lead to poor airflow to areas in your home, hot and cold spots, noisy air ducts, a frozen AC coil and overworked equipment that can fail prematurely. You may also have higher utility bills. High static pressure may be due to dirty air filters that will block airflow or ductwork that is undersized or damaged. Therefore, closing off air supply dampers can increase static pressure. When dampers are partially or fully closed, they are pushing back the air that is being forced against them. The air is then forced through the system by the blower fan. This of course will increase air resistance in the ductwork. In some cases, this can produce the effect you’re looking for and you may not even increase static pressure but doing so can backfire. There are systems with undersized ductwork that deal with static pressure even when the registers are open. If you close them, you can make an existing static pressure problem worse.

What Can You Do Instead?

1. You can have the static pressure in your system measured. If you have too much static pressure you may need to add ductwork, or the blower speed may need to be adjusted.
2. Make sure your HVAC system and ductwork is properly sized. If it’s properly sized, you shouldn’t have to close dampers.
3. Add zones to your HVAC system. Adding zones can eliminate the need to fiddle with supply dampers.

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Too much static pressure inside an HVAC system is never a good situation. You can create a big static pressure problem when you close too many air supply dampers. Contact Air Supply Heating & Air Conditioning to determine if you can safely adjust your dampers, or if you need to consider other options.