How Much Does Air Conditioning Actually Cost to Run?

It's probably the question we get asked most at E3 Engineering. Facility managers and business owners across the South of England want a straight answer, and the honest one is: it depends.

UK business electricity rates in 2026 sit somewhere between 24p and 26p per kWh depending on your contract and consumption. At that rate, a modern 3.5kW inverter split unit running at partial load (the norm with well-sized modern systems) will cost you roughly 15 to 20p an hour. Run it eight to ten hours a day through a hot summer and you're looking at £1.20 to £2 per unit, per day, less than a round of coffees for the office.

Older portable or fixed speed units are a different story, running to 25 to 50p an hour or more partly because they work at full power regardless of how much cooling is actually needed. Inverter technology, standard in Mitsubishi and Daikin systems, adjusts output continuously, so once the room hits your target temperature, the unit eases off rather than cycling on and off at full blast.

For larger systems, a mid-sized VRF or multi-split serving several office zones typically draws 1 to 3 kWh per hour, costing 25p to 75p. A chiller or central system for a large industrial or retail space might run to £0.75 to £2.50 per hour, though that's spread across a much bigger footprint. Cooling accounts for around 5 to 10% of total electricity use in a typical commercial building, and for most buildings, that figure sits below lighting and process equipment, so it rarely drives the headline energy bill.

What Pushes Costs Up

The usual culprits are maintenance and design. Dirty filters and fouled coils can increase energy consumption by 15 to 30%, which is a common finding when we service systems that haven't been touched in a couple of years. Poor building insulation forces the system to work constantly rather than hold temperature, and setting the thermostat to 19 degrees when 23 would do fine adds up fast; every degree below the sensible range adds roughly 8 to 10% to running costs.

SEER ratings matter too, and a system rated SEER 7 delivers around twice the cooling output per kWh compared to a SEER 3.5 unit, which was common in installations from the early 2000s, so if you're comparing quotes, don't just look at the purchase price.

Heat Pumps: Worth the Switch?

A lot of the businesses we work with are now looking at air source heat pumps, either as replacements for gas boilers or as combined heating and cooling solutions. A heat pump delivers three to five units of thermal energy for every unit of electricity it consumes, whereas a gas boiler, even a good one, converts fuel to heat at around 90% efficiency, and electric resistive heating is 1:1, so the heat pump wins in most scenarios. In a poorly insulated building, it runs longer to compensate for losses, which narrows its advantage over gas; fabric improvements and heat pump sizing go hand in hand.

The savings vary significantly depending on what you're replacing and your building fabric, so we model it site by site before quoting a figure. Heating costs typically drop more dramatically than cooling costs, and one integrated system is simpler to manage than two separate ones, which matters when something goes wrong in July.

E3 Engineering is accredited for Mitsubishi Ecodan and Daikin heat pump installations, so if you're weighing up the switch, we can model the numbers for your specific site rather than handing you industry average guesses.

How to Actually Reduce Your Running Costs

Keep the system maintained because it's where most of the avoidable running costs come from. Commercial sites should be serviced at least annually, and twice a year isn't excessive for high-use installations. FGAS registered engineers handle refrigerant compliance at the same time, so you're not juggling separate contractors.

Upgrade if your system is more than ten or fifteen years old, because inverter technology wasn't standard in older installations, and the efficiency gap between a system from 2008 and one from 2024 is real, typically 20 to 40% lower energy use with a modern unit.

Zone intelligently, because empty meeting rooms and unused storage areas don't need cooling. A building management system or even a decent set of smart thermostats makes this easy to automate, and setting target temperatures at 22 to 24 degrees rather than lower saves more than most people expect.

Look at the building itself, because shading windows with blinds or film, sealing drafts, and improving insulation all reduce the cooling load your system has to carry, and these changes often pay back faster than equipment upgrades.

Sub-meter your HVAC and track what it's actually consuming, because the data frequently reveals which units are working harder than they should, and a lot of clients find quick wins this way that no visual inspection would have caught.

For sites with suitable roof space (retail units and warehouses especially), solar PV offsets daytime cooling loads directly. Summer peak generation aligns well with peak cooling demand, and daytime generation can directly offset peak cooling consumption, reducing import from the grid during the hours when cooling load is highest, which is where the financial benefit is most direct.

What This Looks Like in Practice

Our emergency chiller rental work has shown us repeatedly how sharply a neglected system can spike energy bills and how quickly that reverses once it's properly serviced. In Milton Keynes, a three-unit installation correctly sized at the design stage rather than oversized has run for two summers without a callout, and the client's electricity billing confirmed costs in line with our pre-installation estimate.

Getting a Proper Assessment

If you want actual numbers for your site, we'll come out, look at your existing setup, check nameplate data and controls, and give you a calculated running cost rather than an industry average. There's no charge for the assessment. We'll tell you whether your existing system is worth maintaining, what a replacement would cost to run versus what you're paying now, and whether a heat pump makes economic sense for your setup. We've been doing this for over 19 years, with Mitsubishi and Daikin accreditations, FGAS registration, and SafeContractor approval behind us.

Call the team or use the contact form; we'll work from your actual usage data, not industry averages.