Cosy Octopus explained: the windows, the prices and who can join
Cosy Octopus is a smart import tariff built for homes that heat with electricity. It gives you cheap electricity three times a day, charges a premium in the early evening, and asks for a heat pump to join. That last part is less of a hurdle than it sounds: an air-to-air heat pump, the kind that looks like an air-conditioning unit, counts. This article covers the whole tariff: the windows, what the prices look like, who can join and how, how to run heating on it, what goes with it, and the things that catch people out.
What Cosy Octopus is
Cosy is a time-of-use tariff from Octopus Energy for the electricity you import. The price you pay depends on the time of day, in a pattern that repeats every day of the week. It was designed for heat pumps, which run for long stretches rather than in one burst, so instead of a single overnight window like Octopus Go it offers three shorter cheap windows spread through the day, timed to warm a house before breakfast, top it up in the afternoon and settle it before bed.
It is an import tariff only. What you export is paid under a separate export tariff, and you can hold Cosy with or without one. It is also a whole-home tariff: every kWh you import is priced by the clock, not just the heat pump's share, which is what makes it interesting for anyone with a battery, an immersion heater, a car or simply a lot of appliances that can wait for a cheap window. For how a battery in particular should be run on it, see Cosy Octopus with a home battery; this article is about the tariff itself.
The windows
Cosy's day has four kinds of hour. The times are local time, so they stay at the same clock hours when the clocks change in spring and autumn.
| Local time | Band | What it is for |
|---|---|---|
| 00:00–04:00 | Standard | Overnight, on whatever the late-evening fill left you |
| 04:00–07:00 | Cheap | Warm the house and fill the battery before the day starts |
| 07:00–13:00 | Standard | The morning |
| 13:00–16:00 | Cheap | Top the house and the battery up for the evening |
| 16:00–19:00 | Peak | The dearest hours: run on what you stored |
| 19:00–22:00 | Standard | The evening |
| 22:00–00:00 | Cheap | Heat and fill for the night |
Eight cheap hours a day, three dear ones, and thirteen at the standard rate. The surprise for anyone coming from an overnight tariff is the first row: the small hours are not cheap on Cosy. The late-evening window is what carries you to morning, and if your heat pump or your battery needs more than that, the 04:00 window is only a few hours away.
The windows have changed over the tariff's life. Cosy launched at the end of 2022 with two cheap windows, the morning and the afternoon; the late-evening window was added later. Octopus publishes each day's bands on its public price feed, which is how apps including SunHarvest know the exact times for your region, so if the shape changes again the software follows.
What the prices look like
The cheap rate is about half the standard rate, and the peak is about half as much again on top of it. The exact pence depend on your region, because the cost of using the local network differs around the country, and they move when the price cap moves, four times a year. As an illustration, these were the rates in one region in October 2026, including VAT:
| Band | Price per kWh | Against the standard rate |
|---|---|---|
| Cheap | 11.8p | about half |
| Standard | 24.1p | — |
| Peak | 36.2p | about one and a half times |
| Standing charge | 48.6p a day | the same as the standard variable tariff |
Two things in that table matter more than the figures. The standing charge is no different from the ordinary variable tariff: Cosy saves you money only through the unit rates, so a home that imports very little gains very little, as the standing charges article explains. And the cheap price is cheap relative to Cosy's own standard rate; the single overnight window on Go is usually cheaper still per kWh, which is why the comparison between the two is about how much of your use you can move into the windows, not which window is cheapest.
Cosy comes in two forms. The original is a variable tariff: the prices change with the cap, there is no contract length and no exit fee, so you can leave for another Octopus tariff or another supplier whenever you like. Since autumn 2026 Octopus also sells twelve-month fixed versions of Cosy, with the same windows but prices held for a year, and a new version appears whenever the price changes. A fixed version may carry an exit fee; check the terms of the one you are offered before you take it.
Who can join, and the air-to-air question
You need three things: an Octopus Energy account for your electricity import, a smart meter that sends half-hourly readings, and a heat pump at the property.
The smart meter is not optional. A time-of-use tariff can only be billed if your supplier knows how much you used in each half hour, so the meter has to be connected and sending half-hourly data. If yours is a first-generation meter that lost its connection when you last switched supplier, Octopus will usually need to get it talking again before Cosy can start, and that can take a few weeks.
The heat pump is where people assume they are ruled out. Octopus's eligibility covers any kind of heat pump: the air-to-water kind that feeds radiators and a hot-water cylinder, the ground-source kind, and air-to-air heat pumps. An air-to-air heat pump is what most people would call an air-conditioning unit: an outdoor unit, one or more indoor units on the wall, and a refrigerant loop between them. Run one way it cools the room; run the other way it heats it, and in heating mode it is a heat pump in every sense that matters, moving three or four units of heat into the house for every unit of electricity it uses. Modern split systems sold in the UK nearly all do both, and that heating mode is what qualifies you.
So a home with a gas boiler and a single wall-mounted split unit in the living room is, for Cosy's purposes, a heat-pump home. You do not need to have replaced the boiler, you do not need an MCS certificate of the kind a grant-funded air-to-water installation comes with, and you do not need the heat pump to be your only heating. What you need is a fixed installation that can heat; a portable unit on wheels with a hose out of the window is not what Octopus means, and a cooling-only unit does not count either.
When you apply, the form asks what kind of heat pump you have and for its make and model, and Octopus may ask for a photograph of the unit or your installer's invoice before it moves you. The terms have changed more than once since the tariff launched, so read the current eligibility page before you rely on any of this.
How to sign up
- Check your smart meter is sending half-hourly readings. In the Octopus app, the usage graph should show your day in half-hour bars. If it shows a single daily figure, ask Octopus to switch the meter to half-hourly reads first.
- Go to the Cosy Octopus page on Octopus's website, or search for Cosy in the app, and start the switch. You will be asked about your heat pump.
- If you already have an Octopus export tariff or an EV tariff, check that the combination you want is allowed. Cosy pairs with the ordinary export tariffs, but some bundled tariffs that combine import and export, such as Flux, cannot be mixed with it.
- The move takes effect from a date Octopus confirms, usually within a few days once any eligibility check is done. Until then you stay on your current tariff.
- On the first day, look at the prices in the app. You should see the three cheap windows and the peak at your region's rates. If you see a flat price, the switch has not completed yet.
If you later want to leave the variable Cosy tariff, you can move to another Octopus tariff from the app, and the same eligibility rules apply the other way: Go and Intelligent Go want an EV, Flux wants solar and a battery, Agile wants nothing but nerve.
Running a heat pump on Cosy
Air-to-water: radiators and a cylinder
A house holds heat. The idea is to put heat into the fabric of the building, and into the hot-water cylinder, during the cheap windows, and let it coast through the dear hours. In practice that means a heating schedule that runs the heat pump harder, or at a slightly higher target, from 04:00 to 07:00 and again from 13:00 to 16:00, and lets the thermostat drop back a degree or so through the 16:00 peak. The hot water should be heated in a cheap window, with the afternoon one usually the best fit, so that the cylinder is full for the evening. Most heat pump controllers can do this with a simple weekly schedule; some can be told the tariff windows directly.
Do not try to turn the heat pump off through the peak. A heat pump is most efficient running gently and continuously, and a cold house at 19:00 costs more to recover than three hours of setback saved. A lower setpoint through the peak is the right tool.
Air-to-air: a split unit as the heater
An air-to-air unit heats the room's air directly, so there is no cylinder and no building-fabric lag to lean on in the same way, but the same principle holds. Run it in the cheap windows at the temperature you actually want, pre-warming the room before 07:00 and again in the afternoon, and turn it down, not off, for the peak. Because it responds in minutes, it is also the easiest heater to pair with a battery: the battery takes the cheap window too, and then powers the unit through the hours between.
The arithmetic is kind. A split unit heating at a coefficient of performance of three to four turns a cheap kWh into three or four kWh of heat, which works out at three to four pence per kWh of heat delivered. Gas, after a boiler's losses, costs roughly twice that at 2026 prices. So on Cosy an air-to-air unit run in the windows is usually the cheapest heat in the house, cheaper than the gas boiler it sits beside, and the boiler becomes the backup for the coldest hours rather than the other way round.
What goes with Cosy
- A battery. Cosy is unusually good for a battery because it only has to bridge about six hours at a time, so a smaller battery copes with a bigger home than it would on an overnight tariff. The strategy, the summer overlap with solar and a rule set are in Cosy Octopus with a home battery.
- An export tariff. Cosy says nothing about export. Pair it with a flat export tariff for simplicity, or a half-hourly one if you can time your export, as export tariffs explained sets out. You cannot combine it with the bundled import-and-export tariffs such as Flux.
- An EV. A car can charge in any of the windows, though eight hours a day spread in three pieces is less convenient than Go's one long overnight block, and Go's cheap price is usually lower. A household with a heat pump and a car should compare the two on a whole year of its own use rather than on the headline rates.
- Solar. The afternoon window lands on the sunniest hours of a summer day, which is a waste if the battery is already full of sunshine, and a bonus in winter when it is not. The battery article covers making the morning fill conditional on the day's forecast.
- Free electricity sessions. Octopus occasionally gives its customers an hour or so of free electricity, announced a day ahead. On a Cosy home that is a day for a different plan: fill everything in the free hour, skip the paid windows around it, and go back to normal the next day.
Things that catch people out
- Overnight is not cheap. Everything from midnight to 04:00 is at the standard rate. A timer that runs the washing machine at 02:00 because that is what cheap used to mean is paying full price.
- The peak is when you cook. From 16:00 to 19:00 the oven, the hob and the kettle cost half as much again. Without a battery, shifting dinner to after 19:00 or cooking earlier is the only lever; with one, the battery carries it.
- Prices are regional. The windows are the same across Great Britain, the pence are not, so a friend's numbers are not yours.
- The unit rate is not the whole bill. The standing charge is unchanged, so the saving comes only from the use you can move into the windows. A home that can move most of its use, with a battery or a heat pump or both, saves a lot; one that cannot, saves little.
- Half-hourly data goes to Octopus. A time-of-use tariff means your supplier sees your use in half-hour detail. That is the deal.
- Variable means variable. The rates follow the cap each quarter in both directions. The fixed versions trade that for a year's certainty and, possibly, an exit fee.
In SunHarvest
Under Tariffs › Your real tariff, choose Cosy from the Octopus feed and your region's bands sync within seconds, so the spent figures on Home and Energy are valued at the right price for each half hour rather than an average. Octopus publishes each day's prices on the feed a day at a time, and SunHarvest fetches them as they appear.
The Powerwall can be given Cosy's shape as its own tariff so that Time-Based Control holds energy back for the peak on its own, or you can write clock rules for each window edge, with the morning fill conditional on the solar forecast. Rules can be put into groups with a switch each, so a free-electricity day can have its own set: switch the normal group off and the free-hour group on for the day, and a rule in that group can put things back at midnight by itself. Tariff comparison, part of Pro, replays your own metered year against Cosy, Go, Flux and Agile with the battery run the best way for each, which is the honest way to settle whether Cosy is the right tariff for your house.
General information, not financial advice. Tariff terms, prices, eligibility and availability change; check Octopus Energy's current terms before switching. SunHarvest is not affiliated with Octopus Energy.