Here's why closing doors won't save money on central A/C

ST. PETERSBURG, Fla. — It’s a common belief that closing your doors is more efficient for central air conditioners because it funnels air into smaller spaces or cuts off rooms that don’t need to be cooled. 

Google data shows people have been asking this question online for years.

Sally emailed VERIFY to ask if it's true that closing doors to rooms not in use will save money on central air conditioning bills.  

THE QUESTION

Will closing doors save you money on central air conditioning?

THE SOURCES

• U.S. Department of Energy
• American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
• Local HVAC companies including:  Precision Air & Plumbing and The Comfort Authority in Tampa

THE ANSWER

No, closing doors will not save you money on central air conditioning, and may even cost you more. However, it does save you money if you only have a single-room air conditioner, like a window unit.

WHAT WE FOUND

Closing doors doesn’t help with energy efficiency, according to The Comfort Authority in Tampa. It can actually decrease it and increase your monthly bills because it obstructs airflow through your home.

Your home likely has one of two kinds of air conditioners: a central air conditioner, which is designed to cool an entire home through ducts and vents, or a single-room air conditioner, the most common of which are the boxy A/C units that stick out of windows.

“Common central air conditioning problems occur when rooms are closed off and air flow through the home is disrupted,” the U.S. Department of Energy says. “On the other hand, if you have a room air conditioner, the opposite is true.”

Arizona-based Precision Air & Plumbing goes a step further.

“If you have a typically installed air conditioner unit with a central air return, shutting doors is one of the worst things you can do,” Precision says. “It’s right up there with closing vents and beating your outside unit with a sledgehammer.”

The reason for this is because HVAC systems rely on a careful balance of airflow to work effectively. To understand this, we first need to understand how a central air unit works, and what a “typically installed” unit looks like. 

Central air conditioners use a system of supply and return ducts to circulate air throughout a home. The air conditioner sucks in warm air from outside and cools it. Supply ducts carry cool air from the A/C unit into the home through supply vents. This cooled air becomes warmer as it circulates through the home before it flows back into the A/C unit through return vents and ducts. That air is then cooled again and dehumidified in the A/C unit and its heat is pumped back outside while the air re-enters the supply ducts to continue the cycle.

Since central air conditioning units are designed to cool the entire home, most rooms will have supply vents to blow the cool air in. It might sound like this means cool air will go into the room and stay there, but without a proper return system, this is not the case.

But what if I have a window unit?

Closing off unused rooms in houses and apartments with window units will actually reduce cooling costs and make the space you’re using more comfortable, according to Garland Power & Light, a municipality-owned utility provider in Texas.

Window units don’t have supply ducts and vents blowing cool air into every room of a home, and they aren’t built with cooling an entire home in mind. Therefore, trapping the air in the room the window unit is in actually does give it less air to cool and makes it run more efficiently.