Should You Close Vents in Unused Rooms? What Tests Show

By Ray Bennett · Updated 2 October 2026 · 4 min read · Checked against the sources at the end

Should You Close Vents in Unused Rooms? What Tests Show

Short answer

Probably not. A Lawrence Berkeley National Laboratory study found that closing registers raised energy use in the typical house it tested, because the extra duct pressure pushed more air out of leaky ducts. Close more than 60 percent and a furnace can run on its high limit and an AC coil can freeze. Never block a return: Trane says it needs unrestricted airflow.

Should you close vents in unused rooms to save money? It sounds sensible: heat or cool less of the house and the bill should drop. A study by Lawrence Berkeley National Laboratory for the Department of Energy tested exactly that, and found the opposite in the typical house it looked at.

This page explains why, what closing too many registers does to a furnace or an air conditioner, and the better ways to deal with a room you do not use.

Before you start

What to carry: a torch, to check every supply register and every return grille in the house. Ten minutes.

Gas or electric? Either, if the heat or cooling comes through ducts: a gas furnace, a heat pump or a central air conditioner. This is not about mini splits or radiators.

Know the two kinds. Supply registers blow air into a room and usually have a damper you can close. Return grilles pull air back to the system, and Trane says they have no damper on purpose.

What the test and the makers are firm about. Never block a return. Trane says covering a return disturbs the air pressure and airflow, and that it should never be blocked by a magnetic cover, furniture or drapes.

Not more than 60 percent. The LBNL study says closing more than 60 percent of the registers is not recommended: the airflow is so restricted that furnaces may run on the high limit switch and cooling coils may freeze.

A cold house with the furnace on. Trane says to make sure every vent is completely open, because closed or blocked vents stop the heat getting through.

What the test found

The chain of events the LBNL study measured and modelled, and its two rules if you close any at all.

Check 1

Understand why it backfires

The test. LBNL measured how duct leakage changed as registers were closed, then modelled the energy use of a typical California house across a range of climates, duct leakage and numbers of closed registers.

The result. Closing registers led to more energy use, not less. The saving from conditioning less of the house was more than cancelled out by losses from the ducts, mostly from extra leakage.

Where it applies most. The study says the technique is not recommended for California houses whose ducts run outside the heated space, such as an attic or a crawl space.

The least bad way. It found the penalty smallest when the registers farthest from the air handler are closed first, because that only raises the pressure in that one branch.

Returns are different

Check 2

Keep every return open and clear

Why they matter. Trane says return grilles and ducts balance the airflow and pressure in the system, pulling air back to be heated or cooled again.

No covers. A decorative grille is fine, Trane says, but never a solid cover, and never furniture or drapes in front of it.

A filter in the return. If the big return grille holds the filter, change it regularly: how often to change a furnace filter.

Supply registers too. DOE’s Energy Saver guide says to keep warm air registers clear of furniture, carpeting and drapes.

Better ways to use less

What to do instead of shutting registers. Each one lowers the losses rather than raising them.

Check 3

Fix the ducts and the balance instead

Seal the ducts. The LBNL result turns on duct leakage, so the tighter the ducts, the less there is to lose: finding and sealing leaky ducts.

Balance the dampers. DOE says discomfort can often be fixed by clearing blocked registers and stuck dampers, or replacing grilles that do not direct the air well.

Zone it. For a house that really needs different temperatures in different parts, zoning gives each its own thermostat: one room hotter or colder than the rest.

Turn the whole house down. DOE says turning the thermostat down 7 to 10°F for 8 hours a day can save as much as 10 percent a year, and with a heat pump only with a thermostat made for one: what temperature to set.

When closed vents cause a fault

Check 4

Open them and watch

The furnace keeps shutting off. That is the high limit tripping on too little airflow: a furnace limit switch.

Ice on the air conditioner lines. Too little air over the coil lets it freeze: an AC freezing up.

Whistling at the registers. Higher pressure in the ducts can make them noisy: noisy ducts.

Questions people ask

Does closing vents in unused rooms save money?

Not in the LBNL test. It found closing registers raised energy use in the typical house it modelled, because the higher duct pressure pushed more air out through leaks.

Is it bad to close vents in your house?

A few, far from the furnace, does the least harm. The study says closing more than 60 percent can make a furnace run on its high limit and freeze an air conditioner’s coil.

Should I close the return vent in an unused room?

No. Trane says a return should never be blocked or covered, because the system needs unrestricted return airflow to keep the pressure right.

Which vents should I close first?

The ones farthest from the furnace or air handler. The study found that closing those affects only that branch, while closing ones near the air handler raises the pressure everywhere.

Why is one room cold even with the vents open?

Ducts, insulation and the sun all play a part: one room hotter or colder than the rest.

Can closing vents damage my furnace?

Close too many and it can overheat on its high limit switch. The study puts the line at 60 percent of the registers.

Sources: Lawrence Berkeley National Laboratory "Register Closing Effects on Forced Air Heating System Performance" (I.S. Walker, LBNL 54005, November 2003, for the U.S. Department of Energy), Trane "What Is an HVAC Return Air Vent System?" and its gas furnace troubleshooting guide, and the U.S. Department of Energy Energy Saver Guide (2017)