Air conditioning vs a gas boiler

Air conditioning heats as well as it cools, and for a lot of the year it heats more cheaply than a gas boiler. That is true, and it is also the part of the sales pitch that gets oversold.

Here is the version with the caveats left in.

Where it wins clearly

Heating one room rather than the house. This is the whole argument, and it is a strong one. If you work in a home office from nine until five, firing the central heating warms nine rooms to keep one comfortable. A single unit in that room, at around 5.6p per kWh of heat, is a fraction of the cost.

Against any electric heater. A fan heater, an oil filled radiator and a panel heater all deliver exactly one unit of heat per unit of electricity. A heat pump delivers about four and a half. If a room currently runs on electric heating, the saving is immediate and large.

Shoulder seasons. Through October, and again in March and April, outside temperatures sit in the range where a heat pump is at its most efficient. That is a big chunk of the heating year where it is simply the cheaper way to warm a room.

Where the boiler still wins

The coldest weeks. Output falls as the outside temperature drops, because there is less heat in the air to move. Below about 5°C you notice longer warm up times. It keeps working down to around minus 15°C, it just works harder for less.

Hot water. It cannot produce any. None. If you are hoping to remove the gas meter, that is an air to water heat pump conversation and a much bigger job.

Whole house heating. It only warms rooms with an indoor unit in them. Putting a unit in every room to replace a boiler gets expensive quickly, and at that point the sums usually favour air to water.

The things nobody mentions before you buy

It will blow cool air at you occasionally. Frost builds on the outdoor coil in cold damp weather. Every so often the system reverses for a few minutes to melt it, and the indoor unit goes cool while that happens. It is the defrost cycle, it is normal, and there is no way to switch it off.

The outdoor unit drips in winter. Melted frost has to go somewhere. We fit a drain and run it to a suitable outlet, but in a hard frost that drain can freeze and water can spill onto the ground below. Worth deciding at survey whether that matters where your unit is going.

Heat rises, so tall rooms are slow. In a vaulted lounge the warm air collects above your head while the floor stays cool. That is physics rather than the equipment, and destratification fans are the answer.

So what should you actually do

For most houses the honest answer is not either/or. Keep the boiler. Put air conditioning in the two or three rooms you actually spend time in. Use it for heating from September through to the cold snap and again in spring, use the boiler when it is genuinely freezing, and get cooling in July as the part you did not have before.

That is the combination that works, and it is what we fit most often.

The hour by hour figures are broken down in what air conditioning actually costs to run. If you want to see the numbers for your own room and your own tariff, the gas boiler comparison does the sums as you type. And if you would rather have the figures for your actual property, the survey is free.