Living rooms usually draw more electricity per hour: more glass, more people, cooking spill and a bigger unit working in the afternoon peak. Bedrooms usually run more hours, including the night, for a smaller load once the sun is off the glass. Over a heatwave week the bedroom can cost as much or more in total. Both are still often low pounds a day on a split that is holding, not flat out, once you multiply kilowatt-hours by your own tariff. 2026 illustrations only. Survey each room. The installer who sizes them separately will save more than a matching pair of badges.
Three hard afternoon hours against eight gentle ones
A living room with bi-folds on a July afternoon can need the compressor on hard for three or four hours. A bedroom from 11pm to 7am may tick along at a lower electrical draw for twice the time. Three hard hours can beat or lose to eight gentle ones. You only know from the room. Living rooms carry a higher load for a shorter occupied time, often on daytime rates. Bedrooms run longer hours, often a gentler holding load at night. West glass can flip either room into flat-out running.
Similar kilowatt-hours, different clocks
As an illustration, a living room drawing 1 to 1.5 kW electrical at peak for four hours is about 4 to 6 kWh that afternoon. A bedroom drawing 0.6 to 0.9 kW for eight hours is about 5 to 7 kWh. Similar energy, different pattern. Your pence per kWh, and whether the afternoon is on a peak rate, decides the money. Multiply kWh by your tariff. Do not use a national stock figure.
An open-plan diner adds oven heat the bedroom never sees. Closing the kitchen door and extracting steam cuts the cooling hours. In the bedroom, an open window on a hot night lets the unit cool the street. Use the unit with the window shut, and ventilate when the outside air is actually cooler. A setpoint four degrees lower will run longer in both rooms. Bedrooms do not need to feel like a hotel lobby. A moderate night setpoint is the running-cost control you touch every day. Shade on the living room glass is the control you fix once.
A multi-split shares an outdoor unit. If both rooms call together at 6pm, the outdoor unit shares capacity and may run harder. If the bedroom only calls after the living room is off, the evening looks kinder. Tell the surveyor the real timetable. Efficiency still depends on clean coils and a legal, well-ventilated outdoor position.
Planning Portal heat pump siting is a running-cost issue because a choked condenser draws more for the same comfort. GOV.UK F-gas certification is about who installs and handles refrigerant, which is what keeps that efficiency real rather than theoretical. Energy Saving Trust explains the air-to-air heat pump. Per hour, the bedroom is usually cheaper if it is smaller and shaded. Per hot week, it can cost as much or more because it runs all night.
Peak-rate afternoons and a hall unit that cannot reach
If you are in the living room in the afternoon, cool it then, and shade the glass so the unit runs less. Pre-cooling on a cheap night rate does little for an evening room that heats up again through west-facing glass. One bigger unit for both rooms saves money only if the air can actually reach both, which closed doors prevent. Two indoors sized properly usually beat one heroic unit in the hall.
Frequently asked questions
Which room is cheaper to run?
Per hour, usually the bedroom if it is smaller and shaded. Per hot week, the bedroom can cost as much or more because it runs all night. Your timetable decides.
Should I cool the living room in the afternoon on a peak tariff?
If that is when you are in it, yes, and shade the glass so the unit runs less. Pre-cooling on a cheap night rate does little for an evening room that heats up again through west-facing glass.
Does one bigger unit for both rooms save money?
Only if the air can actually reach both, which closed doors prevent. Two indoors sized properly usually beat one heroic unit in the hall.
What if both rooms call at the same time?
On a multi-split the outdoor unit shares capacity and may run harder. If the bedroom only calls after the living room is off, the evening looks kinder. Tell the surveyor the real timetable.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.