How to Block HVAC Vents

August 6, 2021

Do you need to know how to block HVAC vents? While rare, there certainly can be times when you want less air flow to a room; but blocking HVAC vents can have adverse effects on the system. It can increase the pressure of airflow elsewhere. System efficiency may be reduced, moisture may build up (leading to mold), and the extra strain can reduce the life of critical components.

It’s therefore crucial not to block more than a quarter to a third of your HVAC vents at once, but here’s how to block HVAC vents safely if a room is drafty.

How to Block HVAC Vents

  • Manually Close the Vent Grille Covers: These covers usually consist of metal fins that open or close the vent. You can adjust the angle of these fins using a lever on the side. While the vent grille fins don’t create a perfect seal, they can reduce airflow to a more suitable level.
  • Block Off the Vent: You can block the vent by placing a piece of furniture at the opening or purchasing a magnetic damper that’s strong enough to stick to the steel on the wall or ceiling. Plastic sheeting can be placed over the opening as well. Or, you can install a vent grille filter that, while it can improve air quality, doesn’t block air flow all that well.
  • Seal Grille Perimeters: After turning the system off, feel for cold drafts around the vent grille. If you feel something, unscrew the cover and lift it from its mounting. Then apply a 1/8-inch-thick bead of silicone caulk around the edges of the grille. Once the cover is screwed back in place, wait about 12 hours for the sealant to completely dry.

However, a drafty room may be a sign of an air duct leak. If you’ve taken the steps above and still feel excess air flow, have a look at your duct work, checking for leaks around joints in exposed ducts. It may be possible to seal smaller leaks yourself. First, note affected locations with a marker or painter’s tape, and then use mastic sealant or metal tape to seal off the leaks.

Try Partially Closing Vents

You don’t have to completely close air vents to achieve better comfort. For example, partially closing upstairs vents in a two-story home can prevent too much heat from rising to the top, so there’s enough available to keep the lower floor comfort. This will work, while avoiding higher pressures in ductwork, as long as less than 50% of the vents are closed.

Enlist the Help of a Professional Contractor

For builders, heating and cooling systems are a top priority when it comes to properly sizing them for a building or home. But a vent system may not perform to expectations for many reasons. If you’re not familiar with how your HVAC system works, have a contractor inspect your ductwork to determine whether there are leaks and other sealing problems. Excess airflow can be caused by such issues and closing vents won’t resolve them.

Schedule an A/C and heating system inspection at least once a year. Cleaning the ductwork every so often is important too, as it can prevent blockages and indoor air quality issues as well as spot trouble early so a contractor can make the appropriate repairs. And when an A/C, furnace, or other component needs to be replaced, they can suggest energy efficient models that are properly sized for your home.

Contact Fix-It 24/7

We’re a family owned and operated HVAC services company and provide a 24/7 repair service. If you need the airflow in rooms adjusted or have any other issue with your system, our Denver leak detection and repair technicians can permanently fix any problem. Call us at 720-702-7850 to request service.

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