Buying an air conditioner is a strange thing to do for six weeks a year.
Kelvin One is cooling delivered like broadband. £39 a month, first month free, no drilling, no installer, no landlord permission. We own the unit. We deliver it. We service it. When you're finished with it, we come and get it. Your only job is to feel a lot better about July.
£39/month, cancel after 12 months. A conventional installed system quotes at £3,500 to £5,000, tied to a house you may not own next year. This one belongs to us until you don't need it anymore.
Drag the heat up and watch the sun pick up the bill.
The industry sells you a possession. What you actually want is a plumber.
Air conditioning gets sold like a fridge — a proud consumer-durables purchase you research for months, pay for on finance, then live with for a decade. Except unlike a fridge, you only need it for six weeks a year. Nobody buys a season ticket for a train they take twice. So we stopped selling units, and started selling a utility. You pay the monthly bill. We keep the thing working. And when you'd rather not have a big box in the corner, you tell us, and we take it away.
Provisional June record, 2026, with Red Extreme Heat Warnings across England and Wales. The nights people remember are the ones they couldn't sleep. Not the summer they finally installed something.
UK homes with fixed air conditioning. Not because Britain is cool. Because the buying process asks people to decide, up front, that they still want this in ten years' time.
Days a typical UK bedroom needs active cooling in a heatwave summer. If you spent £3,500 on that, you're paying £83 a day. On subscription, you're paying £1.30.
A split system you carry home in two boxes.
Real split-system cooling, the kind that actually chills a whole room, with nothing fixed to your house. The quiet half lives in your room, the working half hangs outside an open window on a no-drill bracket, and a flat line thin enough to close the window on connects the two.
Quieter than the fridge it stands near
The compressor, the noisy part, lives outside the glass. What's in your room is a slim blade you can carry one-handed: 37dB in silent mode, quieter than a library, engineered for the lightest sleepers in the smallest terraces.
Hangs on the window. Leaves no mark.
A 10kg outdoor unit, about the weight of a full shopping bag, sits on a tool-free bracket made for British casement and tilt-and-turn windows. When you move house, it moves with you. Renting is not a reason to be hot.
Close the window on it. Really.
The two halves connect through a flat, sealed line slim enough that the window shuts snugly onto it with the seal kit. No fat elephant-trunk hose, no gale through the gap, and no negative pressure sucking warm air back in. That last one is the reason ordinary portables never quite work.
The hotter it gets, the less you pay
One plug-in solar pack feeds every Kelvin in the house, straight into the units' DC hearts, skipping the conversion losses of bolt-on panels. Peak sun and peak heat arrive together, so on the worst afternoons the sun carries most of the load. Poetic justice, plumbed in.
Cool the rooms you live in, not the house you own.
Whole-house air conditioning is a solution to a problem nobody has. You're only ever in one or two rooms. Kelvin Ones are subscribed per room and talk to each other: they run where you are, pre-chill the bedroom on free afternoon sun before you ever walk in, and take turns drawing power so four units never trouble a single 13-amp plug. Four dumb boxes is a purchase. Four coordinated ones is a system — and a system, unlike four boxes, gets smarter every month it's connected.
The numbers, for people who like numbers.
Every figure is an engineering target benchmarked against the category leader, and each one maps to something you'd actually feel: a silent bedroom, a smaller bill, a window that still closes.
| Type | Mobile split air conditioner + heat pump No planning permission |
| Cooling / heating | 3.5 kW cooling · 3.2 kW heating · one unit, both seasons |
| Efficiency | SEER ≥6.3 (A++) · SCOP ≥4.0 (A+) |
| Indoor noise | ≤37 dB(A) silent mode Quieter than a library |
| Refrigerant | R290, GWP 3 225× cleaner than R32 |
| Outdoor unit | ≤10 kg, tool-free UK window bracket |
| Connecting line | Flat ≤27 mm. The window closes onto it |
| Solar pack (shared) | 800W plug-in panels + 2 kWh battery, DC-direct |
| Install | Self-setup in minutes. No drill. No engineer. No mark left. |
| Power | Standard 13A plug · units coordinate to share the circuit |
| Subscription price | £39 per room per month · first month free · 12-month minimum term · solar pack included |
| What we include | Hardware, delivery, install support, servicing, refrigerant handling, and retrieval when you're finished |
| What you pay | The monthly £39, plus your own electricity to the grid |
Rolls-Royce stopped selling jet engines. We stopped selling air conditioners.
In 1962 Rolls-Royce did something odd. They kept the engines and sold the airlines thrust-per-hour instead. Airlines got predictable bills and better-maintained engines. Rolls got recurring revenue and a fleet they could improve continuously. Everyone won except the salesmen selling one-off engines. That model has since eaten industrial gas, factory air compressors, medical imaging, and pay-by-mile car insurance. It hasn't touched home appliances yet. That's the bit that changes here.
Power-by-the-hour, delivered to your bedroom
Rolls-Royce owns the engines. Airlines pay per flying hour. British Gas HomeCare owns the risk on your boiler. Sunrun owns the panels on 900,000 American roofs and sells you the electricity. Now we own the AC and sell you the summer.
Europe just fell for the hardware. We're fixing the buying process.
Mobile split units sold out across Europe in the 2026 heatwaves. The category works. What's still broken is asking a renter in Hackney to spend £1,500 in June for a summer they'll survive on a fan and rage.
Built for British windows. Cleaner than the incumbent.
Today's kits are built around continental windows and R32 refrigerant with 225× the warming potential of ours. Kelvin One mounts on British casements and tilt-and-turns, and runs on R290, GWP of 3. Because we own the unit, we recover every gram of refrigerant at end of life.
A fleet, not a product
10,000 units on subscription is a hardware business. 100,000 units on subscription is a grid asset. Kelvins in coordinated households can defer their own compressor cycles by fifteen minutes when the grid is under stress, and get paid for it. That revenue subsidises your bill and no manufacturer selling one-offs can compete with it.
Comfort by the room. By the month. Only when you need it.
Start with the room that ruins your sleep. Add more when you're convinced. Cancel any room after twelve months if it wasn't worth it. Nobody measures your walls, nothing gets drilled into them, and nothing ends up on Facebook Marketplace in November.
Renting is not a reason to be hot
No landlord permission, no drilling, no mark left. And no £1,500 asset sitting in a cupboard the next time you move flats. The unit belongs to us; you pay the monthly bill; when the tenancy ends, so does the arrangement, if you want it to.
Bought for July, useful in January
There's a heat pump inside, so the same unit that cools the bedroom in a heatwave heats the home office in winter for a fraction of gas-boiler cost. £39 a month for both jobs makes more sense than £3,500 for one.
One room first. The rest can wait.
Most people start with the bedroom. After the first properly cool night's sleep, the home office and living room tend to follow. Add rooms one at a time. Each one is another £39, and they get on with each other.
Founding 500. First month free.
Reserve now and you're at the front of the queue for the summer 2027 pilot, locked into the launch monthly rate, and your first month is on us. No card charged until we deliver. Cancel any time before then.
Reserve your unit. Pay nothing today.
We ship to Founders in summer 2027. Reserving now locks the £39-a-month launch rate for as long as you're a subscriber, puts you at the front of the queue for the 50-home pilot, and gives you the first month free when we deliver. Your card is never charged today. Cancel any time before we ship, no questions.
- Pilot priority: the 50-home programme is filled from this list, in order of reservation.
- Rate lock: £39 a month held for Founders even if the standard rate rises later.
- First month free: your first invoice, on us, once the unit is in your window.
- A vote, not a newsletter: Founders help decide the first accessories, colours, and pilot cities.
Reservations are numbered. Yours is waiting.
We're not raising to build an appliance. We're raising to finance a fleet.
Two funding tracks, sized for what each is actually for. Seed equity pays for prototype engineering with a UK design partner, refrigeration certification, and the 50-home pilot in summer 2027 — real sleep, real bills, real solar data as the output. Asset-backed debt, from Series A onward, finances the units themselves at a cost of capital appropriate to hardware that generates 8+ years of contracted monthly revenue plus grid-services income. Equity for the risk, debt for the assets. That's how utilities are actually built.