Cosy Octopus explained: is it the best tariff for a heat pump in 2026?

Cosy Octopus is the most widely adopted heat pump tariff in the UK, and for good reason: it's one of the few tariffs built specifically around how a heat pump actually runs. But "most popular" isn't the same as "best for you", and Cosy has a peak-rate trap that catches households who can't shift their heating. This guide explains exactly how Cosy works in 2026, who it suits, where it costs people money, and how to tell if it's right for your home.

If you'd rather skip straight to your own numbers, you can register for a free account, upload your smart meter data, and compare Cosy against every other tariff using your real consumption. For the full field of heat pump tariffs, see our data-driven comparison of the best heat pump tariffs for 2026, and for a sense of what running a heat pump costs overall, our 2026 running-costs guide breaks down the maths.

How Cosy Octopus works

Cosy is a three-rate time-of-use tariff. Unlike a simple Economy 7 (one cheap overnight rate) or a two-rate EV tariff, Cosy splits the day into three price bands:

• Cosy Hours (off-peak): 04:00–07:00, 13:00–16:00 and 22:00–00:00 — eight hours a day, around 51% cheaper than your regional day rate
• Peak: 16:00–19:00 — about 50% above the day rate
• Day rate (standard): all other times

The three cheap windows are deliberately placed. Early morning (before you wake), mid-afternoon (when the house is often empty), and late evening (to top up) are exactly the times a heat pump can pre-heat the building fabric and charge the hot water cylinder efficiently. The 4–7pm peak is when the grid is most stressed and electricity is most carbon-intensive — and, awkwardly, when most homes naturally want heat.

For national-average context, Apr–Jun 2026 Cosy rates sat at roughly 14.5p/kWh off-peak, 33.3p/kWh standard, and 51.7p/kWh at peak. Your exact rates vary by DNO region, and the gap between the three bands is what creates both the opportunity and the risk.

What changed in 2026: Cosy is now a fixed tariff

This is important and often missed. As of March 2026, Cosy Octopus moved to a 6-month fixed tariff with a £25 exit fee if you leave before the term ends. The three-rate structure and the time windows are unchanged — it's the contract terms that changed, not how the tariff behaves day to day.

The practical upshot: you still get the same banded pricing, but switching away mid-term now costs £25. For most heat pump owners committing to a time-of-use strategy that isn't a real barrier, but it's worth knowing before you sign up, especially if you like to switch tariffs frequently.

Who Cosy is best for

Cosy rewards one specific behaviour: shifting heating and hot water load out of the 4–7pm peak and into the three cheap windows. The households that win on Cosy are the ones who can do that.

Heat pump owners without an EV. Cosy is designed for heating-led homes. If your big electrical load is the heat pump rather than car charging, Cosy's three daytime-friendly windows fit better than an EV tariff's single overnight slot.

Homes with thermal mass or a hot water cylinder. The whole game is storing heat when it's cheap. A well-insulated home that holds heat, plus a cylinder you can heat during Cosy Hours, lets you coast through the peak without the heat pump running hard.

People who can schedule and forget. Because the windows never move, you can set your heating schedule once — pre-heat in the early-morning and afternoon windows, avoid 4–7pm — and leave it. No daily price-watching like Agile.

Where Cosy costs people money

The peak rate is the trap. At roughly 50% above the day rate, the 4–7pm window is punishing if you run the heat pump through it at full tilt. A household that can't shift load — no thermal storage, high evening heat demand, heating on demand when everyone gets home — can give back most of the savings from the cheap windows during those three hours.

This is the single biggest reason Cosy disappoints people. The cheap Cosy Hours look attractive, but the tariff only works if you actually avoid the peak. If your home loses heat fast and needs the pump running hard at 5pm in January, the peak rate eats the benefit. For those households, a flatter tariff or a different structure may cost less.

Worked examples: three households on Cosy

Using the three heat pump household profiles from our running-costs guide, here's the estimated annual electricity cost on Cosy (heat pump portion plus standing charge) versus the standard Ofgem cap — assuming a realistic ~50% of heating load shifted into the cheap windows and the peak largely avoided.

National-average estimates based on published Apr–Jun 2026 Cosy rates and typical load-shift assumptions. Figures include the standing charge. Your real cost depends on your DNO region, how much load you can genuinely shift, and your consumption pattern. The right-hand column shows what happens if you can't avoid the 4–7pm peak — the savings nearly vanish.

The contrast between the two Cosy columns is the whole story. Shift your load and Cosy saves the medium household over £300 a year. Fail to avoid the peak and the same household saves almost nothing. Cosy is not a passive saving — it's a tariff that pays you for behaviour you have to actually deliver.

Cosy vs the alternatives, briefly

Cosy isn't the only heat pump option. Where it sits relative to the main alternatives:

• vs Intelligent Octopus Go: Go has a cheaper overnight rate (~8p) but only one window and a higher daytime rate. Go usually wins for heat pump plus EV homes or those with a battery; Cosy wins for heating-led homes that can use the daytime cheap windows.
• vs Octopus Agile: Agile has a higher savings ceiling with automation but needs active management; Cosy is the simpler, schedule-once option.
• vs EDF FreePhase: both are banded/dynamic tariffs that reward load-shifting — see our FreePhase vs Agile comparison for how that family works.

→ Switch to Cosy Octopus and get £50 credit (referral link — supports this site)

Frequently asked questions

Do I need a heat pump to get Cosy Octopus? You need a heat pump, electric radiator or electric boiler to be eligible, but it doesn't have to have been installed by Octopus. If you're mid-installation, you can still switch.

What are the Cosy Hours? Three cheap windows totalling eight hours a day: 04:00–07:00, 13:00–16:00 and 22:00–00:00. Electricity in these windows is around 51% cheaper than your regional day rate.

When is Cosy most expensive? The peak rate runs 16:00–19:00 and costs about 50% more than the day rate. Avoiding heat pump use during this window is the key to saving money on Cosy.

Is there an exit fee? As of 2026, Cosy is a 6-month fixed tariff with a £25 exit fee for leaving before the term ends. The rate structure and time windows are unchanged from the older flexible version.

Will Cosy definitely save me money? Only if you can shift heating and hot water into the cheap windows and avoid the 4–7pm peak. Households that can't shift load may save little or nothing. The only way to know for sure is to model it against your actual consumption.

The bottom line

Cosy Octopus is an excellent tariff for a heat pump owner who can store heat and dodge the 4–7pm peak — its three daytime-friendly cheap windows fit how a heat pump runs better than almost any other tariff. But it's not a free lunch: the peak rate is steep, and Cosy only pays off if you actually shift your load. For a home that can't, the savings can disappear entirely.

The surest way to know whether Cosy wins for your home is to create a free account and upload your smart meter data — we'll run your real consumption against Cosy and every other tariff, region included, so you see the actual numbers before you commit.