Air con vs gas central heating running costs in 2025

The short answer: it depends on how many rooms you heat and how cold it is outside. Here is the long answer with the maths.

What each one costs per unit of heat

Autumn 2025 UK prices at the Ofgem cap:

• Electricity: 24p per kWh
• Gas: 6p per kWh

That looks like a walkover for gas. It is not - because you convert one to the other through very different machines.

Efficiency changes everything

• A gas boiler at 90% efficiency turns 1 kWh of gas into 0.9 kWh of heat. Cost: about 6.7p per kWh of heat.
• An air conditioner with a COP of 3.5 turns 1 kWh of electricity into 3.5 kWh of heat. Cost: about 6.9p per kWh of heat.

At the current 2025 prices, they are roughly level per unit of heat delivered.

But that is not the number that matters. The number that matters is what it costs you to heat the room you are sitting in.

The zoning problem

A gas boiler heats every radiator connected to it. Most UK homes cannot zone room by room. Turn on the boiler for the living room and you also heat the kitchen, the hallway, and the two spare bedrooms.

If you are only using one room in the evening, that whole-house heat is wasted. Real cost per room used: three to four times the theoretical 6.7p.

An air conditioner heats one room. Turn it on when you sit down, turn it off when you leave, forget it existed for the other 20 hours a day. Real cost per room used: close to the theoretical 6.9p.

The actual monthly comparison

A typical UK household, October to March, using one living room 4 hours a night and one bedroom 1 hour before sleep:

• Gas central heating on: about £220 a month for the winter months, £120 in the shoulder months.
• Air con on the two rooms plus gas central heating for background: about £80 for the air con plus £120 for reduced gas central heating = £200 in winter, £80 in shoulder months.

Total saving over a winter: about £250 to £400.

When gas beats air con

The trade flips in three situations:

1. Very cold days. Below zero outside, air con COP drops from 3.5 to about 2.5. Gas gets cheaper per unit of heat.
2. Heating the whole house. If you have small children in every bedroom and need every room warm, gas wins on distribution.
3. Underfloor heating. If the house was designed for whole-floor warm surfaces, gas is the right power source.

When air con wins

The trade favours air con when:

1. One or two rooms actually matter. Bedroom, living room, home office.
2. The house is small or the household is small.
3. The gas boiler is old and you are otherwise about to replace it.
4. Shoulder seasons dominate. September, October, November, March, April - most of the UK heating year is not deep winter.

The install cost catches up quickly

A single-room split system costs £1,800 to £2,700 fitted. At a £250 saving per winter, the install pays for itself in about 7 to 10 winters. It also gives you summer cooling and heats for another five years beyond that on top.

A new gas boiler costs £2,500 to £4,500 fitted and does neither.

Get real numbers for your home

Every situation is different. A good installer will tell you honestly whether an air con install saves you money or whether your setup is better off with gas alone. Get up to 3 quotes and ask each one. Their answer is the number that matters.