Should you block your basement vents to save money on AC?

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Your heating and cooling systems consume a lot of electricity. In fact, they consume about 50 percent of the total electricity used in a regular home. Every homeowner wants to reduce their cooling costs during summer. Can you save energy by closing vents in unused rooms?

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If your house has a basement or an extra bedroom or bathroom that is not used often, you will probably want to save some energy by sealing those rooms off when they are not in use. This might sound logical, but this is not exactly an effective solution.

If you close vents in unused rooms, you are restricting the duct system. Closing one or two vents will probably not be an issue, but if you close several vents, the pressure in your duct system will be too high.

Increased duct pressure can result in the following negative consequences. If duct pressure increases, duct leakage may also increase. Increased duct pressure will also force the ECM blowers to use more energy. In addition, the higher pressure will result in less air flow because it causes the PSC blowers to spin at lower speeds. The low air flow will ultimately lead to comfort problems.

Your air conditioner cools the air flowing through it. If the air flow decreases there is less heat exchange with the air. This will change the coil’s temperature.
If the air flow is low, it will dump less heat into the coil. This will make the coil colder. And when this cold coil comes in contact with the moisture in the air, it may start freezing because of condensation. This might even lead to ice buildup on the coil.

When you close supply vents in certain locations, it does not change what the blower does. It does not change the amount of air the air conditioner moves. Closing one or two vents may be fine, but that too depends upon how leaky or restrictive your air duct system is. Typical duct systems with significantly higher static pressure will not be able to cope with this. By contrast, well-designed systems with sealed ducts and low static pressure are unlikely to encounter many problems if you do not close too many vents.

Closing vents might seem logical, but this can cost you a lot of money. Some super-efficient homes are capable of dividing into zones of HVAC control. This technique will work in those homes. But regular central air conditioning systems are designed to distribute hot or cool air throughout the entire house. If you close a vent in an unused space, the system will cool and pump. However, the air will not be delivered into the space. This will keep the inside of your air ducts frosty. Unfortunately, this will only lead to extra wear and tear.

If you have a big house with lots of unused space, central air conditioning systems may not the best solution because they are meant for heating or cooling the entire home. If you only want to cool a single room, consider buying a basic window unit or a ductless mini-split air conditioner.