Which refrigerant a heat pump uses, and whether it matters

Every heat pump has a sealed circuit of refrigerant, the fluid that boils in the outdoor coil, is compressed, and gives up its heat to the water in your heating system. How a heat pump heats a house explains that cycle. Almost every domestic heat pump sold in Britain today uses one of two refrigerants.

R32 is a fluorinated gas, one of the family regulated as F-gases. It replaced R410A, which was the usual refrigerant until the late 2010s.

R290 is propane, refined to a high purity. It is flammable, and it has almost no effect on the climate if it leaks.

Brochures often present propane as the better choice. In practice the two differ in how hot the water can get, where the unit can stand and who may work on it, and they cost much the same to run at a given temperature.

How hot the water can get

Propane machines from the main manufacturers reach flow temperatures of 70 to 75 °C. Most R32 machines stop at 55 to 65 °C, though some high-temperature R32 models reach 70.

A higher ceiling helps a house that is keeping radiators sized for a boiler, and it lets the cylinder reach the temperatures needed to control legionella with less help from the immersion heater. Hot water with a heat pump covers those temperatures.

Running at those temperatures costs efficiency whatever the refrigerant. Vaillant's own figures for a 7 kW aroTHERM plus give 4.8 units of heat per unit of electricity with water at 35 °C, 2.9 at 55 °C and 2.3 at 65 °C. MIS 3005-D asks installers to avoid designs above 55 °C unless the house needs one, and any design above 55 °C has to come with an alternative at 55 °C or below and an explanation of the difference in running cost.

Running cost at the same temperature

Compared at the same flow temperature, the published seasonal figures are very close. At 55 °C, a 7 kW Vaillant aroTHERM plus (propane) is rated at 3.39, an 8.5 kW Mitsubishi Ecodan (R32) at 3.4, and Daikin's 6 to 8 kW R32 monobloc at 3.28 to 3.35. The test methods differ slightly between manufacturers, and there is no independent British study comparing the two refrigerants in real houses.

On the evidence available, the bill is decided by the flow temperature, the sizing and the controls, which COP and SCOP covers.

Where a propane unit can stand

Propane is heavier than air, so a leak would collect near the ground. Each manufacturer therefore sets a protection zone around its outdoor unit, and the zone must not contain windows, doors, air bricks, vents, cellar entrances, electrical sockets, switches or lights. It must not reach a neighbouring building or a public pavement.

The size of the zone depends on the manufacturer and on how the unit is mounted. For the Vaillant aroTHERM plus standing on the ground in front of a wall, the zone is 2.1 metres wide, runs 1 metre out from the unit, and extends 3.1 metres up the wall above it. In early 2026 Mitsubishi reduced the zone for its Ecodan R290 range so that the restriction on openings applies only within 300 mm of the base. Vaillant's current manual says drains and downpipes inside the zone are not a risk, although some other manufacturers still exclude drains.

On a small plot, or a terrace where the only wall space is beside a back door or a ground-floor window, the zone can rule out the obvious position. The installer should mark it on the site plan before you agree the quotation, and if the unit has to move, the noise calculation in heat pump noise and the 37 decibel rule has to be redone for the new position. R32 outdoor units do not usually carry an equivalent zone, since R32 is classed as only mildly flammable.

Monoblock and split systems

A monoblock heat pump has its whole refrigerant circuit inside the outdoor unit, filled and sealed at the factory. Only water pipes run into the house. Almost all propane heat pumps are monoblocks, which keeps the propane outdoors.

A split system puts part of the refrigerant circuit indoors and joins the two halves with refrigerant pipes on site. Nearly all splits sold for homes use R32.

The difference decides who may install the system. Fitting a sealed R32 monoblock needs no refrigerant qualification, because the installer only connects water pipes. Installing a split system means making joints in the refrigerant circuit, and that requires a person and a company certified to handle F-gases.

Propane is not an F-gas, so no qualification is legally required to open a propane circuit in Great Britain. The Heat Pump Association recommends that anyone who does hold a formal qualification in flammable refrigerants. If a quotation includes future servicing of a propane unit, it is reasonable to ask whether the engineer holds one.

Leak checks

F-gas equipment needs a leak check at least once a year once its charge reaches 5 tonnes of carbon dioxide equivalent. For R32 that is about 7.4 kg. Domestic R32 monoblocks hold far less: 1.35 kg in a small Daikin, 2.2 kg in an 8.5 kW Mitsubishi and 2.7 kg in an 8 kW Samsung. None of them reaches the threshold, so there is no legal leak check for a typical domestic R32 monoblock, and none for any propane unit.

The annual service is a separate matter. Manufacturers' warranties usually require one, and it covers the water side, the controls and the outdoor coil whatever the refrigerant.

What the rules say in Great Britain

Great Britain still applies the F-gas regulation it kept after leaving the EU. As of September 2026 it contains no ban on R32 in domestic heat pumps, whether monoblock or split, and none has been proposed. A government consultation in late 2025 proposed cutting the supply of fluorinated gases more steeply over the next twenty years, but it did not propose banning any heat pumps. In May 2026 the government said it would not legislate this year, so the cut already scheduled for January 2027 goes ahead unchanged.

The EU has gone further. From January 2027 it bans new monoblock heat pumps of 12 kW or less, and new air-to-water splits of that size, that use a refrigerant with a global warming potential of 150 or more, which rules out R32. That measure is explained in the next section. Northern Ireland follows the EU rules on F-gases under the Windsor Framework, so the ban applies there and not in England, Scotland or Wales. Some British websites say the EU ban applies across the UK, which is wrong.

R32 is also not covered by any ban on refrigerant used for servicing, so an R32 heat pump bought now can be topped up and repaired. The overall supply of fluorinated gases is being cut in steps, down to 24 per cent of the original baseline in 2027. That may make R32 dearer over a heat pump's life, though nobody has published a forecast of how much.

The Boiler Upgrade Scheme does not look at the refrigerant. A heat pump qualifies on its efficiency and on being on the scheme's product list, and R32 and propane models are treated the same.

The effect on the climate

Refrigerants are compared by their global warming potential, the warming a kilogram causes over a hundred years relative to a kilogram of carbon dioxide. Under the figures the regulation uses, R32 is 675, R410A is 2,088 and propane is 3.

A study for the government in 2014, based on service records, found that domestic heat pumps lost on average about 3.5 per cent of their charge a year, almost all of it in occasional large leaks. On that rate, a 2.2 kg R32 unit would leak the equivalent of about 50 kg of carbon dioxide a year. Burning 12,000 units of gas in a boiler produces about 2.2 tonnes. The same study found that heat pumps' carbon savings were ten times their refrigerant emissions or more.

A propane unit avoids even that, which is a fair reason to prefer one when the other factors are equal. When an R32 unit is scrapped, the law requires a certified engineer to recover the refrigerant, and that step is what keeps most of the charge out of the air.

Using this when choosing

If the design flow temperature is 55 °C or below, both refrigerants will do the job at much the same running cost, and the choice can follow price, noise, warranty and where the unit has to go. If the house needs higher temperatures, a propane unit or a high-temperature R32 model is needed, and the quotation should show the running cost at that temperature alongside the 55 °C alternative.

For a propane unit, ask to see the protection zone drawn on the plan. For a split system, check that the installer is certified for F-gases. In Northern Ireland, expect new monoblocks from 2027 to use propane or another low-impact refrigerant.