Air Conditioning Isn't Just for Summer
Many people picture air conditioning as a summer luxury. Most modern split systems are actually air-to-air heat pumps. They cool your home in summer and heat it in winter, simply by reversing the direction in which they move heat.
That's the key to their efficiency. An air conditioner doesn't create heat by burning fuel or warming up a resistive element like a fan heater. It moves heat that already exists. In winter it pulls warmth from the outside air, even when it's cold, and brings it indoors. In summer it does the opposite.
Understanding Efficiency: SEER and SCOP
When you compare air conditioning units, you'll see two important ratings:
- SEER (Seasonal Energy Efficiency Ratio): measures cooling efficiency across a typical season. Good modern units sit between 6 and 8.5.
- SCOP (Seasonal Coefficient of Performance): measures heating efficiency across a typical season. Quality units typically achieve 4 to 5.
In plain English, a SCOP of 4 means that for every 1 kWh of electricity you pay for, you get around 4 kWh of heat delivered into your room. A traditional electric heater only ever gives you 1 kWh of heat for 1 kWh of electricity. That makes a heat pump air conditioner roughly three to five times more efficient than plug-in electric heating.
The Tariffs We're Using
To keep things realistic, we've based our figures on typical UK prices at the time of writing:
- Daytime rate: around £0.35 per kWh
- Night-time rate on an EV tariff: around £0.09 per kWh
EV tariffs are designed for electric car owners, but the cheap overnight rate usually applies to your whole home during the off-peak window. If you have one, or are eligible for one, it can transform your running costs. Standing charges aren't included in our figures, and every tariff is slightly different, so always check yours.
What It Costs to Run Air Conditioning in Summer
Cooling is where air conditioning really shines in terms of efficiency. A typical 2.5 kW unit for a bedroom or home office, once the room has reached temperature, often draws just 0.3–0.6 kW of electricity. Modern inverter units ramp down rather than switching on and off.
| Summer scenario | Electricity used | Cost |
|---|---|---|
| Cooling a living room for 5 hours in the afternoon (day rate) | ~3 kWh | ~£1.05 |
| Cooling a bedroom for 8 hours overnight (EV night rate) | ~3.2 kWh | ~£0.29 |
| Home office for an 8-hour working day (day rate) | ~3.5 kWh | ~£1.23 |
Most UK homes only need cooling on hot days, perhaps 30 to 60 days a year. That puts the typical cost of keeping one room cool at roughly £30–£60 per summer. If you mainly cool bedrooms overnight on an EV tariff, it can be well under £20.
And if you have solar panels, your system will often be running at the exact time your panels are producing the most electricity, making daytime cooling close to free.
What It Costs to Run Air Conditioning in Winter
Heating demands more energy than cooling in the UK, so this is where efficiency matters most. The table below compares the cost of producing 1 kWh of heat from different sources:
| Heating method | Day rate | Night rate (EV tariff) |
|---|---|---|
| Electric fan or oil-filled heater | 35p | 9p |
| Air conditioning (SCOP 4) | ~8.75p | ~2.25p |
| Gas boiler (approx., 90% efficient) | ~7p | ~7p |
At the daytime rate, air conditioning is roughly on a par with gas and around four times cheaper than standard electric heaters. On a cheap overnight rate, it beats gas comfortably.
In practical terms, heating a living room for a five-hour evening might need around 10 kWh of heat. Even allowing for lower efficiency on colder days, that typically uses about 2.5–3 kWh of electricity, costing around £0.90–£1.05 at the day rate. The same heat from a plug-in electric heater would cost about £3.50.
A smart trick for EV tariff users is to pre-heat during the off-peak window. Running your system for the last couple of hours of cheap electricity before you wake up can warm the house for around 20–30p, so you need far less heating once the day rate kicks in.
What About Really Cold Days?
It's true that efficiency drops as outdoor temperatures fall, because there's less heat in the air to extract. On a frosty morning at -5°C, a unit might operate at a COP of around 2.5 to 3 rather than 4. Even then, it's still two to three times more efficient than a standard electric heater. Quality modern systems are designed to keep heating reliably well below freezing.
How to Keep Your Running Costs Low
- Choose the right size unit. An undersized system works flat out, while an oversized one wastes energy. A professional heat-loss and room assessment makes a real difference.
- Pick a high SEER and SCOP rating. The extra upfront cost of an efficient model pays back over years of lower bills.
- Use timers and smart controls. Shift as much running as possible to off-peak hours.
- Set sensible temperatures. Around 24–25°C for cooling and 19–21°C for heating keeps you comfortable without wasting energy.
- Keep filters clean and book annual servicing. A well-maintained unit runs more efficiently and lasts longer.
The Bottom Line
Modern air conditioning is one of the most efficient ways to control the temperature in your home. In summer, keeping a room cool typically costs pennies to a pound or so per day. In winter, it delivers heat at a fraction of the cost of electric heaters and can rival or beat gas, especially when paired with a cheap overnight tariff or solar panels.
You get year-round comfort from a single system: cool, restful nights in heatwaves and cosy, affordable warmth when the weather turns.
Figures are illustrative estimates based on electricity prices of approximately £0.35/kWh (day) and £0.09/kWh (night, EV tariff), and gas at approximately 6.3p/kWh. Standing charges are excluded. Actual costs will vary depending on your property, insulation, usage, chosen equipment, and energy tariff.