Does Closing Vents in Unused Rooms Save Energy or Cost More?
With central forced-air heat and ducts in an attic, crawlspace, or garage, closing vents in unused rooms tends to cost more. Lawrence Berkeley National Laboratory found it raised energy use, and closing over 60% of them risks a frozen AC coil or an overheating furnace.
Rooms with their own heater are the exception. If the room has electric baseboard heat or a window unit, turning it down there does save. The rest of this article covers why the ducted case backfires, where the answer changes, and what to do if you close one anyway.
What the Berkeley Lab study found
Iain Walker at Lawrence Berkeley National Laboratory (LBNL) tested the idea in 2003. His team measured in a lab how duct leakage changed as registers (the grilles where air comes into a room) were closed. They fed those measurements into a model of a typical house:
- an 1,800-square-foot, two-story house
- ten supply registers and a single return
- all ductwork in the attic
- heating to 68°F, in three California climates from the coast to the mountains
Result: closing registers increased energy use for that house across a wide range of climates, duct leakage levels, and numbers of closed registers. The unused rooms did need less heat, but the extra duct losses outweighed that. Most of the extra loss came from more air leaking out of the ducts.
Walker’s conclusion is that closing registers is not a viable energy-saving strategy for houses with ducts outside the conditioned space, meaning the heated and cooled part of the house.
At least one utility has handed out the opposite tip. When a homeowner on GreenBuildingAdvisor said his utility had told him to close vents in unused rooms, the site’s editor, Martin Holladay, called that bad advice and pointed to this study.
Why closing a register makes the ducts leak more
Your blower keeps pushing air whether a register is open or shut. Shut one and pressure rises in the ducts, so more air squeezes out through seams and gaps. If those ducts run through the attic, that air heats or cools the attic instead of a room.
The lab numbers show how steep that curve is:
- Leaks at the register boxes: as registers were closed, these rose almost tenfold, from 5% to 55% of the air the blower moved.
- Leaks at the supply plenum: these went from 10% to 35%. The supply plenum is the large box on the furnace that feeds the ducts.
That comes on top of the baseline. ENERGY STAR says a typical duct system already loses about 20 to 30% of the air it moves through leaks, holes, and poor connections.
The safety line: 60% of registers
Closing vents also chokes airflow, and that’s where equipment damage comes in. LBNL treated about a 20% drop in blower airflow as the most that’s acceptable.
Walker says closing more than 60% of registers is not recommended. Two things can happen past that point:
- The furnace may run on its high-limit switch, the safety that shuts the burner off when the heat exchanger overheats.
- The AC or heat pump coil may freeze.
In a ten-register house, 60% is six registers. That isn’t a safe allowance below the line, though. Energy use went up across a wide range of closed-register counts in the study.
Decision table: what to do in an unused room
| Your setup | What to do | Why (source) |
|---|---|---|
| Central forced air, ducts in attic, crawlspace, or garage | Leave the registers open. Use a whole-house thermostat setback instead. | Closing registers raised energy use in this setup (LBNL) |
| Central forced air, ducts in a basement or inside the living space | Leave the registers open; savings from closing them are unproven | LBNL’s verdict covers ducts outside the living space. It didn’t model this case. |
| Any forced-air system | Don’t close more than 60% of registers | High-limit cycling and frozen coils (LBNL) |
| Zoned system (several thermostats with motorized dampers) | Use the zones as designed | Built to shut off airflow to a zone |
| Electric baseboard heat | Heat only occupied rooms and close their doors while heating | BC Hydro’s guidance for baseboard heat |
| Window AC or a ductless unit in that room | Turn that unit off | No shared ducts to disturb |
The proven savings are whole-house. The US Department of Energy says turning the thermostat back 7–10°F for 8 hours a day can save up to about 10% a year on heating and cooling. Our thermostat settings guide lays out a schedule.
For room-by-room heat, BC Hydro, British Columbia’s public electric utility, puts a number on it. It says heating costs can rise about 5% for every degree Celsius above 20°C (68°F). It recommends turning baseboard heaters on only in the rooms you’re using.
“Just close the door” has a catch
The usual fallback is to leave the vent open and close the door. In homes where the return grilles sit only in the central part of the house, that creates a different problem.
Florida Solar Energy Center researchers measured 70 central Florida homes. In nearly all of them, the return grilles were in the central part of the house. With the blower running and interior doors closed:
- Closed rooms averaged +6.2 pascals (Pa) of pressure relative to outdoors, and some reached +37.3 Pa. A pascal is a very small unit of air pressure.
- The central part of the house averaged −2.9 Pa and went as low as −14.7 Pa.
- Outdoor air leaking in rose on average from 0.46 to 0.60 air changes per hour.
That negative pressure in the middle of the house matters if you have gas appliances. The FSEC report says that at about −5 to −10 Pa, most atmospherically vented appliances can spill or backdraft. Those are the ones that vent by natural draft, like many older water heaters and furnaces. Spilling means some exhaust comes back into the house, and backdrafting means the flow reverses entirely. For comparison, Florida’s building code requires return-air paths so the pressure across an interior wall stays at 2.5 Pa or less.
What that means in practice:
- If the unused room has its own return grille, closing its door is less of a concern.
- If it doesn’t, leave the door partly open while the system runs, especially if your house has gas appliances that vent by natural draft.
- Keep the carbon monoxide alarm working wherever you have fuel-burning appliances, and test it monthly.
If you close one anyway
Sometimes a single room is uncomfortably warm or cold, and a nudge to one register is the only quick fix. LBNL’s results give an order:
- Start with the registers farthest from the furnace or air handler. Closing distant registers mostly raised pressure in that one branch. Closing ones near the air handler raised pressure and leakage across the whole system.
- Close one, partway if the damper allows, and stop there. The study found extra energy use across a wide range of closed-register counts, so treat this as a comfort adjustment, not a savings move.
- Stay far below 60% of the house’s registers.
- Watch for warning signs: ice on the refrigerant lines or indoor coil, a furnace that shuts off early and restarts, or rooms that suddenly get harder to heat or cool. ENERGY STAR lists hard-to-condition rooms and high bills as signs of duct problems. If you see ice, turn the AC off, open the registers, and call a technician if it happens again with everything open.
If the real issue is one room that never warms up, the fix may be in the ducts or the room itself. See why one room is always colder than the rest.
Where the money actually goes
If an unused room feels like waste, the duct leakage that closing its vent would increase is the bigger target. ENERGY STAR’s duct-sealing guidance points to leaks, holes, and poorly connected ducts, and to ducts that run through attics, crawlspaces, and garages.
Two cheaper steps come first:
- A clean filter keeps airflow up, which makes the frozen-coil and high-limit problems less likely. See how often to change your furnace filter.
- A whole-house setback on the thermostat, as covered above.
If a winter bill jumped and you haven’t touched anything, this checklist for a higher gas bill walks through the usual causes.
FAQ
Should I close basement vents in summer to push cold air upstairs?
Closing registers doesn’t add airflow. It raises duct pressure, and the extra air mostly leaks out of the ducts instead of reaching the upstairs rooms. LBNL modeled attic ducts in heating season, not basement ducts in summer, so there’s no measured result for this case. Nothing in these sources shows it moves meaningful cooling upstairs. Keep the total well under 60% of registers either way.
Do “smart” vents that open and close on their own fix this?
They still close registers, so the same duct-pressure physics applies. A system designed for zoning, with dampers and controls an installer sizes for your blower, is the version built to handle closed-off areas.
My utility told me to close vents. Who’s right?
For ducts outside the living space, the measured evidence is LBNL’s study, and it found closing registers raised energy use. At least one utility has repeated the old advice. If each room has its own heater, though, room-by-room control does save, which is BC Hydro’s advice for baseboard heat.
Sources
- Register Closing Effects on Forced Air Heating System Performance | Berkeley Lab and the full LBNL-54005 report (PDF) — higher energy use, leakage rising from 5% to 55%, close far registers first, the 60% limit, the study house
- Duct Sealing | ENERGY STAR — 20 to 30% of duct air lost; signs of duct problems
- Unbalanced Return Air in Residences (FSEC-RR-140-06, PDF) — closed-door room pressures, extra infiltration, backdrafting range, Florida’s 2.5 Pa limit
- Electric baseboard heaters | BC Hydro — heat only occupied rooms; about 5% per degree Celsius above 20°C (68°F)
- Closing vents in unused rooms | GreenBuildingAdvisor — utility advice versus the LBNL finding
- Programmable Thermostats | US Department of Energy — 7–10°F setback for 8 hours saves up to about 10% a year
Written and reviewed by peter.bae for Hearth & Habit · Last reviewed October 11, 2026
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