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How much does it cost to air condition an office? Three worked examples

Updated 23 October 2026 · SEO Dons Editorial

How do you work out the cost of air conditioning an office?

Split it into three questions: what the system costs to buy and install, what it costs to run, and what it costs to keep legal and working. This guide puts numbers on the second, using the method on the air conditioning running costs page, and lists what moves the first. The commercial air conditioning cost guide publishes dated installed benchmarks with their source, so they are not repeated here and the examples do not stack one assumption on another.

Every figure in the tables is a labelled assumption except the electricity price: DESNZ's 24.3p per kWh for 2025 (provisional), the average for non-domestic users across all size bands, including the Climate Change Levy. All three examples use a SEER of 5.0. That is above the ecodesign minimums of 4.6 for units under 6 kW and 4.3 for units of 6 to 12 kW using a refrigerant above GWP 150, and it keeps the comparison about size and hours rather than brands. Hours are equivalent full-load hours at the design load, with 400 standing for a light year and 1,000 for a heavy one.

ExampleAssumed floorDesign loadEquipment chosenElectricity a yearCost at 24.3p
1. Single office20 m², 2 people2.5 kWOne 3.5 kW wall split200 to 500 kWh£49 to £122
2. Open-plan office80 m², 10 people8 kWTwo 5 kW ceiling cassettes640 to 1,600 kWh£156 to £389
3. Office floor400 m², 50 people28 kWVRF outdoor unit of about 33 kW with cassettes2,240 to 5,600 kWh£544 to £1,361

The sum for each row is design load times hours, divided by 5.0, times 24.3p. The design loads are illustrative. A real load comes from the people, equipment, lighting, sun and fresh air in the actual room, and a load calculation and survey set the figure that counts.

Example 1: a 20 m² single office with one wall split

Two people, a window on a sunny elevation and a design load of 2.5 kW, so a 3.5 kW wall split is the nearest standard size above it. Cooling delivered is 1,000 to 2,500 kWh a year. Divided by the SEER, that is 200 to 500 kWh of electricity, about £49 to £122 at 24.3p.

The installed price depends on the route as well as the machine: where the outdoor unit can sit, how far the refrigerant pipe and condensate drain must run, whether the wall can be cored, and whether a spare circuit exists or new cabling is needed.

The ecodesign rules cover air conditioners of 12 kW or less. Leak checks start at 5 tonnes of CO2 equivalent, which GOV.UK puts at 2.4 kg of R410A, or 7.4 kg of R32 by dividing 5,000 kg by its GWP of 675, so compare the nameplate charge with those figures.

Example 2: a 10-person open-plan office with ceiling cassettes

Ten people and laptops in 80 m² give an assumed design load of 8 kW, met by two 5 kW cassettes. Cooling delivered is 3,200 to 8,000 kWh, so electricity is 640 to 1,600 kWh, or £156 to £389.

Here the ceiling decides the price. The depth of the void, the tile layout, the fall available for condensate drains or the need for pumps, fire-stopping where pipes pass through, and where the outdoor units sit all change the labour. Whether each unit has its own wired controller or all share a central one changes both the cost and the control over what runs when.

At 10 kW in total the system sits under the 12 kW inspection threshold, but the government's guide counts combined output, so a third unit added later could take it over. Fresh air is a separate item: at HSE's 5 to 8 litres per second per occupant, ten people need 50 to 80 litres per second.

Example 3: a 50-person floor on VRF

Fifty people in 400 m² give an assumed design load of 28 kW, met by one VRF outdoor unit of about 33 kW feeding cassettes in zones. Cooling delivered is 11,200 to 28,000 kWh, so electricity is 2,240 to 5,600 kWh, or £544 to £1,361. Each extra 1p on the unit rate adds £56 a year at the heavy end.

The installed price is driven by items outside the equipment: the spare capacity in the electrical supply, the plant space and lifting for the outdoor unit, refrigerant pipe routes across an occupied floor, fire-stopping, integration with the building management system, commissioning, and whether work has to be phased out of hours.

At 28 kW the system needs an energy assessor's inspection at least every five years, and the penalty for not having the report is fixed at £300. The leak-check band depends on the nameplate charge: for R410A, 24 kg takes a system into the six-monthly band, and for R32 that is about 74 kg. Fresh air for 50 occupants at HSE's rate is 250 to 400 litres per second.

What do the three examples leave out?

  • Ventilation. Cooling units recirculate room air, and HSE asks employers with recirculating systems whether they bring in some fresh air. It is priced separately, as on the commercial ventilation cost page.
  • Servicing and leak checks. These recur every year; the servicing cost page shows how the price is built.
  • The inspection report above 12 kW, which is separate from servicing.
  • Tariff effects such as standing charges and contract changes, which move the £ figures but not the kWh.

Whether any of this is worth carrying is a separate decision, covered in is air conditioning worth it for a business.

How do you turn an example into a figure for your own office?

  1. Ask for a load calculation, not a rule of thumb. Occupancy, equipment, lighting and glazing differ between offices of the same size.
  2. Take the declared SEER of the equipment proposed, from the product data, rather than assuming 5.0. The guide to SEER shows how to read it.
  3. Estimate equivalent full-load hours from the occupied hours and how hard the system works on hot days.
  4. Use the unit rate from your own contract in place of 24.3p.
  5. Ask each bidder to list electrics, outdoor-unit siting, builder's work and out-of-hours working as separate lines.

You can send an enquiry through the form on this site to ask for quotes against your own load and plan.

Sources

Common questions

Does a 10-person office need an air conditioning inspection?

Only if the combined effective rated output of its air conditioning is more than 12 kW. The government’s guide counts sets of smaller units together, so two 5 kW cassettes are under the line, but adding a third unit could cross it. Above 12 kW the inspection must be repeated at least every five years.

Do office air conditioners bring in fresh air?

Not by themselves. HSE asks employers with recirculating systems whether they bring in some fresh air, and gives 5 to 8 litres per second per occupant as the rate the supply should not normally fall below. Ventilation is therefore a separate line in the budget.

Where do the SEER and hours assumptions come from?

The SEER of 5.0 and the 400 and 1,000 full-load hours are assumptions chosen to show the method. The legal minimum SEERs of 4.6 and 4.3 are in the ecodesign regulation. Replace all of them with the declared SEER and your own hours.

How much would a price rise add to the running cost?

Multiply the electricity used by the change in the rate. For the 50-person floor at the heavy end, 5,600 kWh means each extra 1p per kWh adds £56 a year. DESNZ’s annual averages moved between 20.9p and 27.2p per kWh from 2022 to 2025, so the contract rate matters.

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