How air conditioning works, and what it costs to run.

What's actually happening inside

A split system doesn't create cold, it moves heat. It carries warmth out of your room using a refrigerant loop, and in winter it simply runs in reverse to bring heat in, which is why it's so efficient. Follow the cycle below.

The basics, in plain English

An air conditioner works on the same simple idea as the fridge in your kitchen: it doesn't make cold, it moves heat from one place to another. A liquid called refrigerant flows around a sealed loop, soaking up warmth in one spot and letting it go in another. This is proven, century-old technology, the very same engineering that quietly keeps your fridge and freezer running for years on end, just scaled up to warm and cool a whole room.

The clever part is that it works both ways. In summer it lifts the heat out of your room and releases it outside, leaving cool, filtered air behind. In winter it simply runs in reverse, gathering warmth from the outside air, even on a cold day, and bringing it indoors. So a single system keeps you comfortable all year round, and for many homes it can replace both a cooling unit and a good deal of the heating.

Because it moves heat rather than burning fuel or glowing an element to create it, it gives out far more warmth than the electricity it draws. A modern unit typically delivers around 3 to 4 units of heat for every 1 unit of electricity it uses. That is what makes these systems so efficient to run, and a genuinely smart, lower-carbon choice for a comfortable home.

What does it cost to run?

Running cost is one of the hardest things to pin down when you are researching air conditioning, because it depends on your room, the weather and how you use the system. The figures below are rough estimates only, a ballpark rather than a promise. They show roughly how much electricity a unit tends to use to hold a comfortable temperature once the room has got there. Cooling a hot room down, or warming a cold one up from scratch, uses more for the first while; steady running is much gentler.

Prices used: the Octopus Go tariff (July 2026), about 28p per kWh in the day and 8.5p per kWh overnight (its cheap window runs 00:30 to 05:30). Rates vary by region and change over time, so treat these as an illustration and check your own tariff.

Estimated guide figures for maintaining a room once it is up to temperature; cooling down or heating up from cold uses more at first. Actual usage and cost depend on your unit, your room, your tariff and the weather, so treat these as a starting point, not a quote. If you have solar panels or a home battery, you can run it for even less, from your own generation or stored off-peak power. We'll confirm the exact sizing and your fixed price for your property at a site visit before we install.

What would it cost to run today?

Using today's real hourly forecast for Birmingham, here's the estimated electricity cost of holding a room at your chosen temperature, hour by hour. Pick your room size, set the target, and switch between heating, cooling and both.

Or drag the two green markers on the axis to set your own hours.

Today's forecast for Birmingham: high of 18°C around 2pm, low of 13°C around 1am.

If you already have solar panels, the two are a natural match. Because air conditioning uses relatively little electricity for the comfort it gives, a bright day can often run it for next to nothing, turning your own sunshine straight into cooling or heating. On a hot, sunny afternoon your panels frequently produce more than the house needs, and that surplus can go into keeping you cool rather than being exported for a few pence, with the same true for heating on brighter winter days. Add a home battery and you can store daytime generation to keep things running into the evening. It won't be free in every hour or every season, and the exact savings depend on your system, your usage and the weather, but pairing solar with air conditioning is a noticeably greener, lower-cost way to stay comfortable.

Frequently asked questions