Is it alright to close the air conditioning vents in unused rooms?

Friday, August 10, 2018

While it would seem sensible to close the air vents (supply registers) in unused rooms to save a little on your heating/cooling cost each month, it doesn’t work out that way. Here’s four reasons why:

1) Let’s start with the fact that a well-designed HVAC system has ducts that are sized—going from a larger to smaller cross-section as they get further from away from the air handler—to get just the right amount of air flow to each room, without too much or too little at either end of the duct runs. Then the air vents they connect to are also calibrated to match the rooms they serve. A system that is correctly designed and installed is called “balanced.” Closing any of the air vents fouls up the equilibrium of the design, causing changes in the amount of air delivered to the vents that remain open, often in an unpredictable way. 

2) Closing an air duct increases the back-pressure on the blower, making it slow down and work harder, which shortens the life of the motor—an expensive component to replace.

3) The additional pressure in the ducts increases leakage at the connections of duct components. It’s estimated that as much as 20% of the conditioned air flow in the average home’s duct system leaks out into the attic anyway, but closed ducts will increase the leakage and possibly force open more seams.

4) The back-pressure of a closed air vent at the end of a long duct run often forces cold air leakage just behind the air vent during the summer, which causes condensation wetness around the leak in a hot, humid attic. The result is sometimes mold growth at and behind the air vent. Here’s an infrared photo of a closed and leaking vent.


    So, closing the vents in unused rooms causes problems that are not offset by the minor cost savings created, and we recommend that you don’t do it.

    Also see our blog posts Will closing doors reduce my heating and cooling costs? and Why is my air conditioner not cooling enough?

• • • • • • • • • • • • • • • • • • • • • • • • • • • • 

  To learn more about heating and air conditioning systems, see these other blog posts:

How can I find out the SEER of my air conditioner? 

My air conditioner won't turn on. What's wrong? 

How can I find out the size of my air conditioner? 

How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

Where is the air filter for my central air conditioner and furnace? I can’t find it? 

Does an old air conditioner use more electricity as it ages? 

How did homes stay cool in Florida before air conditioning? 

What is wrong with an air conditioner when the air flow out of the vents is low?

Why has the thermostat screen gone blank? 

Why does it take so long to cool a house when an air conditioner has been off for a while? 

Why is my air conditioner not cooling enough? 

What are the most common problems with wall/window air conditioners?  

Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 


Water Heaters

Water Heater Age

Wells

Septic Tank Systems

Structure and Rooms

Plumbing Pipes

Termites, Wood Rot

& Pests

Sinkholes

Stairs

When It First

Became Code

"Should I Buy A..."

Park Model Homes

Site

Shingle Roofs

Safety

Stucco

Remodeling

Wind Mitigation Form

Roof and Attic

"Does A Home

Inspector...?"

Pool and Spa

"What Is The Difference Between..."

Radon

Brick

Plumbing

Concrete and

Concrete Block

Metal Roofs

Foundations

Modular Homes

Rain Gutters

Mold, Lead & Other Contaminants

Condominiums

Older and

Historic Houses

Crawl Spaces

Mobile/Manufactured Homes

Building Permits

Life Expectancy

Clay Soil

Insurance

Floors

Insulation

Toilets

Exterior Walls & Structures

Generators

Common Problems

HUD-Code for

Mobile Homes

Garages and Carports

Flat (Low Slope) Roofs

Electrical Panels

Sprinkler Systems

Electrical Receptacle Outlets

4-Point Inspections

Hurricane Resistance

Frequently Asked Questions (FAQ)

Home Inspection

Heating and Air Conditioning

Building Codes

Fireplaces and Chimneys

Inspector Licensing

& Standards

Energy Efficiency

Washers and Dryers

Electrical

Kitchens

Doors and Windows

(placeholder)

Cracks

Electrical Wiring

Click Below  

for Links

to Collections

of Blog Posts

by Subject

Plumbing Drains

and Traps

Appliances

Smoke & CO Alarms

Aging in Place

Top 5 results given instantly.

Click on magnifying glass

for all search results.

Bathrooms

Lighting

AFCI, CAFCI,

DFCI, & GFCI

Sinks

Air Conditioner & Furnace Age/Size

Attics

Electrical Switches

Siding

Search

This

Site

Water Intrusion

Electrical - Old

and Obsolete

(placeholder)

Foundation Certifications

Tiny Houses

How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactured and modular homes

About Us