Britain just hit 35°C in May. The politicians are arguing about air conditioning. They’re all missing the point.

The week the conversation finally caught up

Tuesday 26 May 2026. Heathrow and Kew Gardens recorded 35°C. The hottest May day in British history — two days running. Monday night at Kenley airfield in Surrey did not drop below 20°C overnight, officially classified as “tropical” by the Met Office. The Climate Change Committee chose this same week to warn that heatwaves “threaten the British way of life.”

And by 9:35pm Tuesday evening, the political fight was on.

The Conservatives pledged to reverse the so-called “air con ban” — the 2021 building regulations that direct developers to use passive cooling (windows, shutters, ventilation) before fitting air conditioning in new homes. The shadow energy secretary framed it as “Why should Britain be one of the only countries to not have air conditioning?” Labour has kept the regulations in place. The Tories want to bin them. “Let’s make Britain cool again.”

It’s a genuinely interesting political moment. It’s also missing the point entirely.

The argument both sides are having

Strip away the slogans and the underlying question is: should British homes have air conditioning, yes or no?

Conservatives say yes — let people choose, the grid is cleaner than it was, the climate has changed. Labour and the building regulators say no by default — air-con uses too much energy, passive cooling is cheaper, focus on the building fabric.

Both positions are arguments about a 1990s technology choice: split air-conditioning units, refrigerant pipework running through walls, separate machines for heating and cooling, F-gas refrigerants in every room, one set of boilers for winter, a different set of boxes for summer.

That is not the choice in front of British homeowners in 2026.

What’s actually changed under the surface

While the politicians have been arguing, the Boiler Upgrade Scheme has quietly become one of the most generous home energy grants in the world. As of 28 April 2026, the Ofgem grant structure is:

• £7,500 towards an air source heat pump (air-to-water) — the standard route for the majority of UK homes
• £7,500 towards a ground source heat pump (including water source and shared ground loops)
• £9,000 from July 2026 for households currently heated by oil or LPG — typically off-gas-grid rural properties. Announced by the UK Government on 21 April 2026.
• £2,500 towards an air-to-air heat pump — for direct-electric-heated homes where a full hydronic system makes no sense
• £5,000 towards a biomass boiler
• 0% VAT on qualifying heat pump installations until 31 March 2027

Ofgem awards one grant per property. The £7,500 air-to-water grant and the £2,500 air-to-air grant cannot be stacked. The grant pays for the heating system that replaces your boiler — and a properly designed modern heat pump now delivers heating, hot water, and cooling from a single machine.

That last word is the part the political debate has not caught up with.

Why hydronic beats air-to-air every time it actually matters

Before going further, the technical fork in the road matters. There are two ways to deliver heat or coolth around a house:

Air-to-air moves refrigerant gas through pipes running through the building, with indoor units that blow conditioned air across an indoor coil. The split air-con on every Spanish balcony works this way.

Air-to-water (hydronic) keeps the refrigerant entirely outside in a sealed unit. Water carries the energy around the house through insulated pipes, delivering it via radiators, underfloor pipework, or fan coils.

The hydronic approach wins on five metrics that genuinely matter.

1. Efficiency

Water has roughly four times the volumetric heat capacity of air. A litre of water carries far more energy than a litre of air at the same temperature differential. Hydronic systems can coast on stored thermal energy in the pipework and emitters, modulate smoothly at low loads, and integrate with thermal storage tanks for off-peak operation.

Real-world Seasonal Coefficient of Performance (SCOP) figures consistently come in higher on hydronic than air-to-air in equivalent buildings. The difference is largest at part-load conditions, which is where UK heat pumps spend most of their operating hours.

A 200-litre buffer tank holding water at 50°C stores about 9 kWh of usable thermal energy. There is no equivalent on an air-to-air system — when the compressor is off, the system delivers nothing. Hydronic systems can pre-heat overnight on cheap electricity, store the energy, and release it through the next day. Time-of-use tariffs (Octopus Cosy, Octopus Go, Economy 7) make this a real running cost advantage.

2. Underfloor heating and cooling

This is the single biggest advantage of hydronic systems and the one British marketing tends to undersell.

The same warm water that heats your floors in winter can run chilled in summer. Underfloor cooling at a sensible temperature (16–18°C, above the dew point) gives genuinely comfortable radiant cooling — no draughts, no noise, no condensation, no maintenance. It works because the whole floor becomes a giant low-grade cooling surface, removing heat from the room by radiation and conduction rather than by blowing chilled air at occupants.

Underfloor cooling is standard in new commercial buildings across continental Europe and increasingly in residential premium new-builds. Occupants describe it as “the room is just cool” — no visible machinery, no fan noise, no sense of being in an air-conditioned environment.

A reversible air-to-water heat pump is what makes residential underfloor cooling possible. The £2,500 air-to-air route does not enable any of this.

3. Hot water

Air-to-air systems do not make hot water. They heat and cool room air. That is all they do.

If you install an air-to-air system as your primary heating and cooling, you still need a separate hot water solution. Most homeowners end up keeping the gas boiler for hot water (which defeats the point of decarbonising) or installing a separate immersion heater (which is the least efficient way to make hot water that exists).

Air-to-water systems heat water as their primary output. The same machine that warms your floors in February heats your hot water cylinder year round. One system, one grant, hot showers included.

4. Refrigerant containment

This is the health and safety point, and it leads into the longer discussion below.

On a hydronic system, the entire refrigerant charge stays in the outdoor unit — a small (under 1 kg) sealed circuit in a sealed box outside the house. Water carries the energy indoors. The refrigerant never enters habitable space.

On an air-to-air split, refrigerant pipework runs through the building fabric to each indoor unit. More joints, more pipe length, more leak paths, more refrigerant indoors. A typical multi-split installation has 20–40 metres of refrigerant pipework running through walls and ceilings.

This matters for two reasons. First, leak rates. Field studies of split air-con systems consistently find lifetime leak rates of 5–15% of charge per year — refrigerant is escaping into the building and into the atmosphere throughout the system’s service life. Second, occupant exposure. When that pipework eventually fails (and over 15 years, some of it will), the refrigerant ends up in the rooms it serves before it ends up outside.

Hydronic systems have neither problem. Water leaks make a mess. Refrigerant leaks make a regulatory problem.

5. Architecture

A hydronic system is invisible.

No outdoor units bolted to the side of every bedroom. No drainage pipes weeping down brick walls. No racket from indoor fan units. Just radiators, underfloor pipework, or smart fan coils — clean, modern, quiet.

For period properties, listed buildings, and architecturally sensitive sites, the hydronic platform is often the only viable option. UK planning officers are increasingly hostile to visible split AC units, particularly in conservation areas.

The refrigerant question your installer probably won’t raise

Here is the part of the conversation that the UK heat pump industry has been quietly avoiding.

Almost every air-to-air split sold in the UK runs on a fluorinated refrigerant — R32 (a hydrofluorocarbon), R410A, or newer “low GWP” hydrofluoroolefin blends like R454B and R1234yf. The £2,500 air-to-air grant will, in practice, fund installs of these systems by the tens of thousands across the next two summers.

What is happening at European regulatory level should make every UK homeowner pause before signing for one of those installs.

The Universal PFAS Restriction Proposal

In January 2023, the national environmental authorities of Germany, Denmark, the Netherlands, Norway, and Sweden — five of the most scientifically rigorous regulators in the world — jointly submitted to the European Chemicals Agency (ECHA) a proposal to restrict the entire PFAS group of substances under REACH (the Registration, Evaluation, Authorisation and Restriction of Chemicals regulation). The proposal is known as the Universal PFAS Restriction.

It explicitly names the following refrigerants within its scope:

• HFC-125
• HFC-134a
• HFC-143a
• HFO-1234yf
• HFO-1234ze(E)
• HFO-1336mzz(Z) and HFO-1336mzz(E)

These chemicals are the components of common commercial refrigerant blends. R410A is a 50/50 blend of HFC-32 and HFC-125. R454B (currently being marketed as a “next generation low-GWP” replacement for R410A) is a blend of HFC-32 and HFO-1234yf. R1234yf is a single-component refrigerant used in mobile air-conditioning.

Where the proposal stands today

The proposal has moved through ECHA’s scientific committee process during 2025 and 2026:

• 3 March 2026: ECHA’s Risk Assessment Committee (RAC) adopted its opinion on the PFAS restriction proposal
• 11 March 2026: ECHA’s Socio-Economic Analysis Committee (SEAC) agreed its draft opinion
• 30 October 2025: ECHA held a public consultation webinar on the draft opinion
• August 2025: The five-country authorities published their updated proposal incorporating responses to the initial consultation

The matter now sits with the European Commission for the final regulatory decision. The Commission’s restriction proposal will, on the published timeline, become law during the second half of this decade with transition periods that vary by application.

The TFA pathway

The proposed restriction targets two things. First, the f-gas refrigerants themselves. Second — and this is the part the chemical industry would prefer to keep quiet — their atmospheric degradation product, trifluoroacetic acid (TFA).

When these refrigerants leak into the atmosphere (and over a 15-year system life, every system leaks some), they undergo photo-oxidative degradation. The breakdown percentages are well established in the ECHA proposal text:

• HFO-1234yf: 100% conversion to TFA within a few weeks of release
• HFC-134a: up to 20% conversion to TFA

TFA is then deposited back to earth in rainfall. It accumulates in water, soil, plants, and ultimately in human blood, breast milk, and drinking water. It does not break down further. It meets the OECD definition of PFAS that ECHA uses — any substance containing at least one fully fluorinated methyl or methylene carbon atom, without any hydrogen, chlorine, bromine, or iodine attached to it.

TFA is, in the formal regulatory sense and on the OECD definition adopted by ECHA, a forever chemical.

The health basis

The European Food Safety Authority (EFSA) is currently reviewing the health-based reference values for TFA, with a conclusion expected in 2026. ECHA’s restriction proposal is based on the precautionary principle applied to substances of very high persistence, mobility, and demonstrated bioaccumulation across the wider PFAS class.

PFAS as a class have established or strongly indicated links to a range of human health effects: liver function effects, kidney function effects, thyroid function effects, immune system effects, certain cancers, and reproductive and developmental effects. The TFA-specific health work is being completed now. The regulatory precaution is already moving — and is moving from countries whose environmental science is internationally regarded as the most rigorous in the world.

What this means for the natural refrigerant position

R290 propane and CO₂ (R744) are natural refrigerants. Neither contains fluorine. Neither degrades into TFA or any other PFAS.

• R290 (propane, C₃H₈): atmospheric breakdown products are CO₂ and water vapour. GWP = 3.
• R744 (carbon dioxide): atmospheric residence as CO₂; no further breakdown. GWP = 1.

Neither is in scope of the F-gas Regulation or the ECHA PFAS proposal. Neither faces restriction risk under current or anticipated European chemical regulation.

Reversible R290 + iZONE: one machine, three jobs

The Karnot iHEAT R290 range — 9.5 kW through 30 kW — is an air-to-water heat pump using propane as the refrigerant. GWP of 3. Zero PFAS pathway. Entire refrigerant charge sealed in the outdoor unit, under 1 kg, in full compliance with IEC 60335-2-40.

In winter, iHEAT pulls heat from outdoor air and delivers hot water at up to 75°C to your cylinder, radiators, underfloor pipework, or fan coils. COP of 4.0 to 4.5 — four kilowatts of heat for every kilowatt of electricity.

In summer, the cycle reverses. Chilled water at roughly 7°C (for fan coil cooling) or 16–18°C (for underfloor cooling) circulates through the same pipework. The house gets cooler. Same machine. Same install. Same MCS certificate. Same BUS grant.

iZONE smart fan coils are the indoor side of the story. They are designed as direct radiator replacements — they bolt to the same wall positions, connect to the same flow and return pipework, and look like clean modern panel emitters rather than industrial AC units. They run almost silently (typically under 35 dB at low speed). In winter, warm air. In summer, cooled and dehumidified air. No separate AC system on the wall. No outdoor box dripping condensate onto the patio.

For new-builds or major refurbishments, underfloor heating and cooling is the premium option — invisible, draught-free, and pairs perfectly with the iHEAT R290. The same heat pump runs both seasons through the same buried pipework. Most homeowners who experience underfloor cooling for the first time describe it the same way: cool air just is there, with no noise, no draught, no machinery in sight.

Two to four iZONE units, or an underfloor circuit, or a combination of both — the hydronic platform is flexible. The point is: one heat pump, one set of pipes, one grant, full climate control all year round.

What this looks like for a UK homeowner this week

A typical 3-to-4 bed home with a gas boiler, looking at the forecast, thinking we cannot do another summer like this one:

• iHEAT R290 11.5 kW outdoor unit
• 4 to 6 iZONE smart radiator replacements (or an underfloor cooling circuit, or both)
• Hot water cylinder
• MCS-certified install through a Karnot trade partner
• £7,500 BUS grant deducted from the quote upfront (£9,000 if you’re currently on oil or LPG, from July 2026)
• 0% VAT until March 2027
• Zero F-gas, zero PFAS pathway, propane stays sealed outside

You exit winter with lower bills than the gas boiler delivered. You exit summer with bedrooms that are actually sleepable in a heatwave. Hot water on tap year round. One install, one contractor, one certificate, one grant, one refrigerant — a natural one, with no European regulatory cloud hanging over it.

The alternative is what most UK households are doing right now: buying a plug-in air-conditioner from a high street retailer, running it on a 3 kW circuit, watching the meter spin, putting it back in the loft in October, and venting fluorinated refrigerants that ECHA is in the process of restricting.

For MCS installers reading this

If you are an MCS-certified installer and you are not offering reversible R290 hydronic systems as your standard residential package this summer, you are leaving money on the table and your customers are buying portable units from Argos.

Karnot iHEAT is MCS certified and BUS eligible. iZONE smart fan coils integrate cleanly into the same install as direct radiator replacements. Underfloor heating and cooling is fully supported. Trade pricing delivers strong margin per job. Next-day delivery from a UK 3PL warehouse. Free MCS compliance pack with every unit.

The customer conversation this week writes itself: you’ve just had the hottest May on record, you’re going to install heating anyway because the gas boiler is on the way out, why not install the system that does heating, hot water, and cooling on a single grant — with a refrigerant that isn’t under active European restriction.

The bigger picture

The political argument this week is about whether to allow air conditioning. It’s the wrong argument. The right question is which architecture solves heating, hot water, and cooling in one machine — using a refrigerant that European regulators are not actively trying to restrict and that won’t be detected in your grandchildren’s drinking water.

Reversible R290 air-to-water heat pump. Smart fan coil radiator replacements and underfloor pipework. Full BUS grant funding the install. Natural refrigerant with no PFAS pathway, no F-gas exposure, and no European regulatory cloud.

That is the conversation Britain should be having. We are having it now because the weather forced it. The grant infrastructure has been quietly ready for two years. The technology has been ready longer than that. The politicians, and most of the industry, are just catching up.

Heat. Hot water. Cool. One system. One grant. Both seasons. No F-gas in your home.