Why leaving interior doors open can help (or hurt) your heating — room-by-room guide

The culprit might be a habit no one thinks about: whether you leave interior doors open or closed. The answer isn’t one-size-fits-all. It’s room-by-room, and it can save you real money.

The first cold snap of the year arrived on a Tuesday. Kettle on, heating humming, I walked from the cosy kitchen into a hallway that felt like a church nave. The living room door had been left ajar after the school run, and warm air was drifting upstairs like a balloon escaping a child’s hand. Downstairs, the radiators kept working; upstairs, the landing sat there, smug and toasty, heating absolutely no one.

I started closing doors, then opening them again, like a low-budget science experiment with slippers. The difference was immediate. Heat moved, yes, but it didn’t behave. The thermostat told one story. The rooms told another. The strangest part?

Heat has habits — doors set the rules

Hot air is lazy. It rises, pools, and leaks through gaps that look innocent until the bill arrives. Doors are the sluice gates of that river, either channelling warmth where you need it or letting it wander off. In British homes with radiators, most heat moves by a mix of convection and gentle air currents. A closed door changes the current in seconds.

We’ve all had that moment when a bathroom feels like a sauna while the hallway feels like January. That’s not magic. It’s pressure differences and steam trying to escape. Home energy assessors often find a few pascals of pressure between rooms when doors are shut — small numbers, big comfort swings. In houses with ducted heat, those tiny pressures can stop warm air returning to the system entirely, like putting your thumb over a straw.

Think of heat like water in buckets. If the thermostat sits in the hallway with the door open to a warming room, it thinks the whole home is warm and shuts the boiler early. If the living room is closed off, that same hallway stays cooler and calls for more heat. One habit, two very different outcomes. *Heat loves a path.*

Open or closed? It depends on your system and the space

Start with your heating system. With radiators and TRVs, doors decide how each room forms its own mini-climate. Keep doors closed in rooms you want to heat quickly or keep cosy; open them when you want to share surplus warmth with adjacent spaces. With forced-air or heat pumps using ducts, **keep doors open** unless every room has a proper return path (a return grille, a transfer vent, or a generous undercut). No return path means pressure builds, airflow drops, and efficiency takes a hit.

Now look at the story your thermostat tells. If it lives in a hallway, leaving doors to the warmest room open can trick it into stopping the heat too soon. Close that door during warm-up, then crack it after. Kitchens and bathrooms are a special case: moisture is a heat carrier and a mould risk. **Close doors to trap steam**, run extraction, then open once the mirror clears. Your paint, windows, and lungs will thank you.

Let’s be honest: nobody really does that every day. So aim for rhythms, not rules. Daytime: if the household lives downstairs, keep bedroom doors closed to stop a stairwell chimney robbing heat. Evening: open doors between lived-in rooms if you want even comfort. Night: if heating is off and you prefer cooler air, **crack the bedroom door at night** to balance CO2 and freshness without losing all the warmth.

“Doors are cheap thermostats. Open is share, closed is focus. The trick is deciding what you want the air to do, then letting it.”

• Living room with radiator: Close during heat-up for faster comfort; open later to share warmth with the hall.
• Hallway thermostat: Keep the warmest adjacent room’s door mostly closed while heating, so the hall reads honestly.
• Kitchen: Door closed while cooking; extractor on; door open after to bleed residual warmth safely.
• Bathroom: Door closed for showers; fan or window cracked; open 10–15 minutes later to release gentle heat, not wet air.
• Bedrooms: Daytime doors closed if heating downstairs; at night, a small gap helps fresh air without gutting heat.
• Loft conversion: Door closed in windy weather to stop stack-effect losses up high.
• Box room/home office: Door closed if you want fast warmth; TRV set to the lowest comfortable setting.
• Forced-air homes: Door open unless there’s a return grille or transfer vent in that room.
• Wood burner: Nearby doors ajar to spread radiant gains, but keep stair door mostly shut so heat doesn’t race upstairs.
• Pets: Leave a small gap or fit a transfer grille so air — and the cat — can move freely.

The room-by-room map

Living room: If it’s your evening nest, shut the door for the first half-hour of heating. You’ll feel the difference in minutes. Open it later if you want to take the edge off the hallway chill without confusing the thermostat too much.

Kitchen: It generates its own heat. Treat the door like a damper — closed when cooking to contain heat and smells; fan on; then open to share the leftover warmth. Greasy air isn’t comfort. It’s maintenance work waiting to happen.

Bathroom: Steam is a heat balloon and a mould magnet. Door closed, fan on during and after showers. When the mirror clears, open the door to let residual warmth drift out, not soggy air. Small habit, big pay-off for paint and plaster.

Bedrooms: Daytime, keep them closed to stop the stairwell acting like a chimney. Evening, open a hand’s width if you want a more even upstairs. Overnight, a crack balances fresh air with warmth, especially if the door is tight to the carpet and starves airflow.

Hallways and landings: They’re the referees of your heating game. A too-warm hall lies to the thermostat; a too-cold hall makes the boiler overwork. Nudge TRVs low in hallways, keep draughts in check, and match door habits to what the thermostat actually reads.

Home office or box room: Small rooms warm fast and overheat faster. Shut the door for quick comfort during calls, then open briefly to equalise. If you’re on a heat pump, try a smaller setpoint jump rather than slamming the door and spiking demand.

Loft conversions: High spaces hoard heat. In windy weather, closed doors prevent warm air from being pulled up and away by the stack effect. On still days, opening the door later lets warmth drift down to the landing without gutting downstairs.

Utility rooms: They leak more, live colder, and don’t need pampering. Keep the door shut during main heating periods. Open after a dryer cycle to borrow the residual warmth into adjacent spaces.

Make doors work for you all season

Think in patterns, not perfection. Cold morning? Close lived-in room doors for a quick warm-up, especially with radiators. Midday sun on the front room? Open that door and let “free heat” wander. Wet laundry day? Close doors around the drying rack and ventilate to prevent condensation from chasing the warmer air.

Winter storms push air into one side of a house and suck it from the other. If the wind hammers the front, keep upstairs doors closed to stop heat escaping up and out. Calm, bright days are sharing days: open doors between rooms that feel pleasantly warm and those that lag behind.

Small hardware tweaks multiply the gains. A 10–20 mm undercut beneath tight doors helps airflow, especially in ducted homes. Simple stick-on seals stop draughty gaps where you don’t want air to flow. Transfer grilles above doors solve bedroom pressure issues without living with open doors forever. None of this needs to be perfect. It just needs to be kinder to how air wants to move.

Season, system, and habit — the gentle blend

There isn’t a single right answer because every house and family is a little weird, in a good way. The rule that works is the one that respects both your system and your day. Radiators respond well to focus: close to warm fast, open to share later. Ducted heat responds to freedom: open unless you’ve created a return path. Kitchens and bathrooms are their own planets — keep the warmth, manage the wet, release the leftovers.

Watch what your thermostat sees. Watch where your breath fogs a pane first. If you feel a cold river on your ankles when you open a door, you’ve found a pressure story to fix with a gap, a grille, or a gentler door habit. You don’t need gadgets to notice these things. You just need to walk the house for five quiet minutes and listen to the air. The rooms will tell you what to do next.

FAQ :

• Should I leave bedroom doors open at night?For fresh air and steadier temperatures, a small gap works well. If you prefer a cooler sleep, go wider — especially if heating is off overnight.
• Will closing doors damage my boiler or heat pump?No. Closing doors changes room temperatures, not system pressures in hydronic setups. In ducted systems, avoid fully closing many doors unless each room has a return path.
• What about homes with a wood burner?Keep nearby doors ajar to spread radiant gains to the hall and adjacent rooms. Close the stair door to stop heat racing upstairs unused.
• Do TRVs change the “open or closed” advice?They help. Close a door and the TRV will throttle once the room meets setpoint, saving energy. Open later to share gentle warmth without overcooking the room.
• How big should the gap under interior doors be?For airflow in ducted homes, 10–20 mm is common. If rooms feel stuffy with doors shut, consider a transfer grille or a wider undercut rather than living with doors permanently open.