Garden room heating — heat pump vs infrared vs electric radiator

The heating conversation happens late in most quotes, and it shouldn't. Choosing between a heat pump, an infrared array and a plug-in electric heater has knock-on effects on the electrical spec, the ceiling detail, the interior finish and the year-one running cost — none of which are easy to change once the shell is up. This is the working brief we use with every UK client.

The three options, honestly

Option 1 — reverse-cycle air-source heat pump (2-3 kW split system). Wall-mounted internal head, condenser unit outside on a small bracket. Also cools in summer. Runs at a coefficient of performance (COP) of 3.5-4.0 in mild UK winter conditions, meaning £1 of electricity buys £3.50-4.00 of heat. Install cost £1,600-2,200 fitted.

Option 2 — infrared ceiling panel array. Two to four 400-800 W panels flush-mounted in the ceiling, heating people and surfaces directly rather than heating the air. Instant-on, silent, invisible. Runs at 100% efficiency but no COP multiplier — £1 of electricity buys £1 of heat. Install cost £900-1,400 fitted.

Option 3 — plug-in oil-filled electric radiator. Zero install cost, no design implications. Same efficiency as infrared (100%, no COP) but heats the air rather than the surfaces. Install cost £0-180 depending on whether it's DIY or bought as part of the fit-out.

Running-cost numbers for a working week

Modelled on a well-insulated 4.2 × 3.2 m SIP shell (our standard Forge spec), 8 hours a day, 5 days a week, Feb 2026 electricity price 27p/kWh, external temperature 5°C:

• — 01Heat pump — average draw 0.6 kW over the day. £5.68/week (£147 per heating season).
• — 02Infrared array — average draw 1.4 kW over the day. £15.12/week (£393 per heating season).
• — 03Plug-in radiator — average draw 1.5 kW over the day. £16.20/week (£421 per heating season).

Across a five-year window the heat pump is £1,230 cheaper to run than an infrared array, £1,370 cheaper than a plug-in radiator. The install premium is recovered by year three.

Where each one actually suits

• — 01Heat pump. Any garden room used more than 8 hours a week. Full-time home offices, gyms, cinemas, therapy rooms, studios. The COP multiplier is the reason.
• — 02Infrared. Occasional-use rooms — a garden bar, a hobby workshop, a guest sleepover space. Instant heat when you arrive, no wasted running cost when the room is empty. Also worth it in a north-facing room where the visible heat source (the ceiling panel warming a person directly) is more comfortable than a warm-air system.
• — 03Plug-in radiator. Rooms with no dedicated electrical spec, or clients who genuinely want zero fixed heating and are happy pushing an oil-filled radiator in and out. Rare — we specify this maybe twice a year.

The spec deltas each choice triggers

Heat pump — needs a 20 A dedicated circuit, an external condenser bracket, a 65 mm penetration through the wall for the refrigerant lines, and (for cooling in summer) a condensate drain to a soakaway. All of that is straightforward if it's spec'd at the design stage, expensive to retrofit.

Infrared — needs a dedicated 16 A radial and (usually) a smart thermostat. Panel positions are set at ceiling design because they replace a light fitting or coordinate with track lighting.

Plug-in radiator — no spec impact but needs the standard socket ring uprated to handle a 2 kW continuous load (which is fine on our default 32 A ring, but worth flagging).

“The right answer for a full-time home office is almost always a heat pump. The right answer for a weekend garden bar is almost always infrared. Getting this the wrong way round is where most of the running-cost complaints come from.”

— Arden & Oak — design lead

What we spec by default

Every home-office quote we send includes a 2.4 kW reverse-cycle heat pump as standard, mounted at the design stage. Studio, gym, cinema and therapy-room quotes get the same treatment. Bars, workshops, hobby rooms and pool houses get infrared as standard, with heat pump as an upgrade.

For the wider running-cost brief see the winter garden-room running-costs article. For the office spec conversation, see the South Devon office guide.