Compared with its sources on 5 November 2026
What size air conditioner do you need?
For a room with a normal ceiling, allow about 2.0 to 2.5kW for 15 to 25 square metres. The table below gives a first estimate, but tall ceilings, bay windows and top floors in Leamington Spa homes can all push the figure up. A proper survey should always settle the final choice.
Get a quote
Name, number, postcode. We call you back to talk it through.
How do floor area and capacity match up?
| Room size | Approximate cooling output |
|---|---|
| 10 to 15 m² | 1.5 to 2.0kW |
| 15 to 25 m² | 2.0 to 2.5kW |
| 25 to 35 m² | 2.5 to 3.5kW |
| 35 to 50 m² | 3.5 to 5.0kW |
These are iHeat's figures for standard ceiling heights, updated in May 2026. Measure length times width in metres to get your floor area. Source: iHeat.
How do kW and BTU relate?
About 3,412 BTU per hour equals one kilowatt, which makes a 3.5kW unit roughly 12,000 BTU. Glow Green's own table runs from 8,000 BTU for 9 to 14 square metres up to 25,000 for 42 to 60, and it calls that a general estimate. Different tables will give you slightly different answers, which is a good reason not to rely on any one of them. Source: Glow Green.
When should you go up a size?
- High ceilings. There is more air to cool. A Regency first floor can be well over the standard height these tables assume.
- Big windows facing south or west. Leamington's bay windows catch a lot of afternoon sun.
- Top floors and lofts. Heat rises from below and comes through the roof.
- People and machines. Computers, televisions, lighting and bodies all add heat. Offices and studios should be worked out from their load. See office air conditioning.
Sources: iHeat; Glow Green.
Is bigger always better?
No. A unit that is much too big reaches the set temperature quickly and then keeps cycling on and off. That is less comfortable, can leave the air clammy, and may wear parts faster. It also costs more to buy. A unit that is too small will run flat out on the very days you need it. The right size holds a steady temperature on a hot afternoon without much noise.
Do you size differently for heating?
Sometimes. Output falls as the outside air gets colder, and the Wellesbourne station averages about 47 days of air frost a year. If you are relying on the unit for winter heat, look at its heating output at low outdoor temperatures, not just the headline cooling figure. See air-to-air heat pumps. Source: Met Office.
What about server rooms and comms cupboards?
Ignore floor area and work from the power your equipment draws, because almost all of it becomes heat. A 900W machine gives out 900W. Our server room page shows the method. Source: Server Room Environments.
Common questions
Can one unit do two rooms?
Rarely well, unless they are open to each other. Doors stop the air moving, so each closed room should have its own indoor unit.
How much difference does insulation make?
A lot. A well-insulated room holds its temperature with less work, while an old roof or single glazing can push you up a size.
Is the size on the box the cooling output?
Often, but check whether it is the cooling or the heating figure, as they differ. A portable's BTU figure may not compare directly with a split's.
Sources
Before you ring
These details let us give you a better answer on the first call.
- Your postcode
- Flat, house or workplace
- Whether the building is listed
- Which rooms, roughly how big, and which way they face
- Who owns the outside walls, if you lease or rent
Ready to have it done? Air conditioning in Leamington Spa explains what we fit and look after, and where we travel.
If you want this done
Air conditioning installation
Survey, consents, fitting and start-up, in that order.
Home air conditioning
Quiet systems for bedrooms, top floors and family rooms.
Conservatory air conditioning
Makes a glass room or garden office usable in July and January.
Other guides
How much does air conditioning cost?
Fitted prices, electrics, running costs and the extras people forget.
Does air conditioning need planning permission?
The permitted development conditions, with the Leamington exceptions.
Can you have air conditioning in a listed building?
Consent, siting and humidity, for Grade II and Grade II* homes.
Is air conditioning allowed in a flat?
Leases, freeholders, planning limits and flats above shops.
Is air conditioning for a bedroom worth it?
How hot is too hot, what size to buy and what a night costs.
Air conditioning for a loft conversion: what works?
Why lofts overheat, and where units go under a sloping roof.
How do you check the F-gas register for an installer?
Company certificates, personal qualifications and who to ask.
Portable against fixed air conditioning: which wins?
An honest comparison, including when a portable is the better buy.
Want us to call you?
Tell us where you are and what is too hot or too cold. Or ring 01926 967778.