No, completely closing vents isn’t a reliable way to save money on central heating

If there was something you could do that would save you money and make you live more comfortably at the same time, why wouldn’t you do it? Many Americans hope they’ve found a solution to do just that by closing vents in unused rooms while their heater runs in the wintertime.

The belief that this strategy could work is common enough that countless local HVAC companies from around the country have published blog posts titled “Is it okay to close HVAC vents in unused rooms?”

THE QUESTION

Can you reliably save money on heating by completely closing vents in unused rooms?

THE SOURCES

• Reddi Heating & Cooling, an HVAC company based in Wichita, Kansas
• Apollo Home, an HVAC company based in Cincinnati, Ohio
• Energy Vanguard, a firm that trains and consults companies on building performance
• Prime Energy, a renewable energy company based in New England
• Iain Walker, a member of international HVAC engineering society ASHRAE

THE ANSWER

No, you cannot reliably save money on heating by completely closing vents in unused rooms. Completely closing vents runs the risk of increasing your heating costs and damaging your HVAC system. But partially closing certain vents might save you a little money without the risks.

WHAT WE FOUND

American homes can have a number of different heating systems and heat distribution systems. If you have vents, like most homes do, you probably have a forced-air system. The U.S. Department of Energy says these are compatible with furnace heaters and heat pumps, which often share the same system used for your central air conditioning.

In July, VERIFY found that closing off unused rooms by shutting doors and vents does not save you money on central air, and could even cost you more by making your system less efficient. Completely closing off vents won’t save you money on central heating, either.

More from VERIFY: No, closing doors won't save money on central A/C

Completely closing your vents risks damaging your HVAC system and pumping up energy costs, but partially closing certain vents might save you a little money without all the risks.

Apollo Home, a Cincinnati-based HVAC company, says you can partially close the one or two vents furthest away from your furnace to save a little money while keeping enough air flow moving through the system to keep it running properly so it doesn’t cost you more down the line.

The sweet spot to close your vents is about 50-74% of the way, according to Prime Energy, a New England renewable energy company.

But even doing this, you’ll likely only find modest energy savings. Closing vents can only save you so much money because the rooms inside your home aren’t insulated from one another, Iain Walker, a member of ASHRAE, or the American Society of Heating Refrigeration and Air Conditioning Engineers, told VERIFY in an email.

Without insulation, Apollo Home warns, the hot air won’t stay in just one room, even if you’ve completely closed off the vents in every other room of your home.

“Cold rooms in a warm house act like a heat sink. It’s a fact of physics: Heat is naturally drawn out of warm areas into colder zones,” Apollo Home says. “Keeping one or more rooms unheated inside an otherwise warm house tends to suck heat energy out of the heated areas and into the cold rooms through interior walls that aren’t insulated. The furnace cycles on and off more frequently to compensate for the heat loss, actually raising energy costs and diminishing indoor comfort. What you thought was helping improve home comfort actually detracts from it.”

So it doesn’t help much, sure. But why would completely closing some vents make it potentially more costly to heat your home? 

The answer: Your HVAC system is designed to heat and cool your entire home, and attempting to force it to heat just part of your home risks damaging it and hurting its efficiency.

“Your HVAC system was built to be ‘balanced,’” Wichita-based Reddi Heating & Cooling says. “This means that the ductwork was sized for the amount of air going in to equal the volume of air going out. The blower pulls air from the house through the return ducts and then pushes it back into the house through the supply ducts. Thus, closing vents changes the balance of your HVAC system.”

A traditional central heating system won’t know that you’ve closed off a vent, and won’t change the amount of air it pumps through the system based on you closing it, Apollo Home says. So completely closing vents makes the system overwork to heat a space that is much smaller than the space it’s built for. 

Since that additional air has nowhere else to go, it backs up within your home’s ducts, which Walker said causes pressure to begin building up within your ductwork. That pressure makes the ducts leak more of the heated or cooled air they carry, and therefore leave you with a less efficient system overall.

A less efficient system has to work harder to heat or cool your home, which is why your energy costs then go up.

HVAC systems also need air to flow back into the system from your home to work properly. Without enough air flow, the heat exchanger in your system could overheat and become cracked, Energy Vanguard, a firm that trains and consults companies on building performance, says. A cracked heat exchanger can leak carbon monoxide into your home, which can make you sick and even kill you.

One last potential problem with completely closing your vents, an issue noted by Walker and Energy Vanguard, is that the slightly colder air in the rooms not getting the heat from your vents can cause moisture issues and mold growth in those rooms. 

There are, of course, other reasons you might be tempted to close off your vents entirely, such as a temperature imbalance in your home. The Department of Energy notes that many homes with such issues have air pressure imbalances that can only be fixed with solutions more permanent than closing off vents, such as adding grilles to transfer air between rooms.

If you have an issue with your HVAC system that you want to fix, such as a temperature imbalance, you should talk to your local HVAC technician to find the right solution for the system unique to your home.