Buying AC · 4 Min read · updated September 2026

How to choose an AC system for your home

System types, brands, efficiency ratings, room sizing, and what to look for in an installer — everything you need to make a confident decision without wading through technical specs.

In this guide

→ Step 1 — How many rooms do you need to cool?
→ Step 2 — What size system do you need?
→ Step 3 — Which brand should you choose?
→ Step 4 — What efficiency rating matters?
→ Step 5 — What to look for in an installer
→ The quick decision checklist

Step 1 — How many rooms do you need to cool?

This is the first decision and it shapes everything else. The answer determines whether you need a single room or multi-room system — and has a significant effect on cost.

One room → single split system. One indoor unit, one outdoor unit. The simplest and most affordable option.
Two or more rooms → multi-room system. Multiple indoor units sharing one outdoor condenser. More efficient and neater than multiple single systems.

If you’re only certain about one room now but might want more later, read our guide on single room vs multi-room AC before deciding.

Step 2 — What size system do you need?

AC systems are rated in kilowatts (kW). Choosing the right capacity for your room size matters — too small and it won’t cool effectively; too large and it’ll cycle on and off inefficiently.

Room Size	Recommended Capacity	Multiple Room
Up to 20m²	2.0–2.5 kW	Small bedroom
20–35m²	2.5–3.5 kW	Double bedroom, home office
35–50m²	3.5–5.0 kW	Large bedroom, living room
50m²+	5.0 kW+	Large open plan spaces

Your installer will calculate the right capacity precisely during the site visit — accounting for ceiling height, window size, orientation, and insulation. Don’t worry too much about specifying capacity yourself before you speak to them.

Step 3 — Which brand should you choose?

The residential AC market in the UK is dominated by a handful of Japanese manufacturers. All are reliable — the differences are in efficiency, noise levels, aesthetics, and warranty terms.

Daikin — Premium

The market leader globally. Excellent efficiency ratings, whisper-quiet indoor units, and strong long-term reliability. Higher equipment cost but lower running costs over time.

Mitsubishi Electric — Premium

Particularly strong on indoor unit aesthetics — the MSZ-LN range is the most design-conscious residential unit available. Comparable efficiency and reliability to Daikin.

Samsung — Mid-range

Good efficiency at a lower equipment cost. Wind-Free technology on premium models eliminates the direct cold draught feeling. Solid reliability record.

Our honest view: for most UK residential installations, Daikin or Mitsubishi Electric are worth the premium. The efficiency advantage reduces running costs meaningfully over a 10-year system lifespan, and the noise levels on premium inverter units are significantly lower than mid-range alternatives.

Step 4 — What efficiency rating matters?

Modern AC systems carry EU energy efficiency ratings. The scale runs from A+++ (most efficient) down to D. All systems Temlo installs are A-rated or above.

SCOP — Seasonal Coefficient of Performance (heating)

How efficiently the system provides heat across a full year. A SCOP of 4.0 means the system produces 4kW of heat for every 1kW of electricity. Good: SCOP 4.0+. Excellent: SCOP 5.0+.

SEER — Seasonal Energy Efficiency Ratio (cooling)

How efficiently the system provides cooling across a full season. A SEER of 6.0 means the system produces 6kW of cooling for every 1kW of electricity. Good: SEER 6.0+. Excellent: SEER 8.0+.

Sound level (dB)

Indoor unit noise level in decibels. Premium inverter units operate at 19–25dB at minimum speed — quieter than a whisper. Budget units can be 35dB+, which is noticeable in a bedroom. Bedroom standard: under 25dB.

Refrigerant type

All new systems should use R-32, which has a global warming potential of 675 — significantly lower than older R-410A (GWP 2,088). Temlo only installs R-32 or equivalent low-GWP systems.

Step 5 — What to look for in an installer

The equipment is only half the equation. A well-specified system installed poorly will underperform. These are the non-negotiable qualifications for anyone installing AC in a UK home.

REFCOM registered — required by law for anyone handling F-Gas refrigerants in the UK. Check the REFCOM register at refcom.org.uk.
F-Gas certified — the engineer must hold a current F-Gas qualification and provide an F-Gas certificate on completion.
Public liability insurance — minimum £2M cover. Ask to see proof before any work begins.
Verified customer reviews — check Google or Trustpilot, not just the installer’s own website.
Fixed written quote — a reputable installer will always provide a written fixed quote after a site visit. Never agree to work on a verbal estimate alone.

Every Temlo installer meets all five standards — vetted before onboarding, monitored after every job.

The quick decision checklist

Run through these five questions and you’ll have everything you need to brief an installer confidently.

How many rooms do I want to cool? One room → single split. Two or more → multi-room.
What are the room sizes in m²? Measure length × width. Your installer uses this to specify the right capacity.
Do I need planning permission? House → probably not. Flat, listed building, or conservation area → check our planning guide.
What’s my budget? Single room from £1,800. Multi-room from £3,200. Premium brands add £200–£500 to equipment cost.
Is my installer REFCOM registered and F-Gas certified? Non-negotiable. Check refcom.org.uk if in any doubt.

Get a free estimate at Temlohome.com — your installer will advise on planning during the site visit.