Heat pump running costs on Cosy

Reviewed May 2026 against current Octopus Cosy, Energy Saving Trust and heat-pump control guidance.

Cosy Octopus is built for homes that can move electric heating away from the expensive late-afternoon period. It can suit a heat pump well, but it is not magic. Your running costs still depend on the property, the heat pump design, flow temperature, hot water use and how much comfort you are willing to trade for cheaper time slots.

If you are still deciding whether a heat pump is the right technology, start with the heat pumps and Octopus overview. This page is for the next question: once you have a heat pump, how should you think about Cosy running costs?

The Cosy price shape

Cosy has three daily rate bands:

• Cosy Hours (13.7p–15.3p/kWh): 04:00-07:00, 13:00-16:00 and 22:00-midnight
• Standard rate (31.6p–34.9p/kWh): most other hours
• Peak rate (49.2p–54.2p/kWh): 16:00-19:00

Octopus says the Cosy Hours are 51% cheaper than the regional day rate, while the peak rate is 50% above the day rate. The actual pence-per-kWh figures vary by region and tariff version, so use the tariff comparison tool or Octopus’s Cosy page for current local prices before making a switch.

The useful structure is simple: you get eight cheap hours spread through the day, then a short expensive window in the early evening. A good Cosy setup is less about chasing every cheap unit and more about keeping the heat pump away from 16:00-19:00 without making the house uncomfortable.

What affects the bill most

Cosy changes the price of each unit. It does not change how many units your home needs.

For heat pumps, the biggest running-cost drivers are usually:

• the heat demand of the building, especially insulation, draughts and exposed walls
• the system design, including radiator size, underfloor heating and how well rooms are balanced
• the flow temperature, because lower flow temperatures usually mean better heat-pump efficiency
• the heating curve and controls, especially whether weather compensation is enabled and properly tuned
• hot water use, cylinder size and how often the system has to run at higher temperatures
• your comfort target, since a warmer home costs more to maintain

Energy Saving Trust guidance is a useful reminder that real-world heat-pump efficiency is better judged by seasonal performance than by a single laboratory CoP figure. If your installer gave you an SPF or seasonal performance estimate, keep it with your tariff comparison because it tells you more than the heat-pump model name alone.

A sensible Cosy schedule

A common starting point is:

04:00-07:00: let the heat pump bring the house up gently before the day starts. Avoid a huge overnight setback, because forcing a cold house back to temperature can make the heat pump run harder.

13:00-16:00: use the afternoon cheap period as the main top-up before the peak window. This is often the most valuable Cosy slot for space heating because it sits just before 16:00-19:00.

16:00-19:00: reduce heating demand as much as comfort allows. Some homes can coast through this period, while lighter or draughtier homes may still need some heat. Do not let the tariff push you into a cold house.

22:00-midnight: use the late cheap period for a modest top-up, hot water or both. If your home loses heat quickly overnight, a smaller steady setback may work better than fully switching the heat pump off.

Treat these as starting points, not rules. A well-commissioned heat pump usually prefers steady low-temperature operation. If aggressive on/off scheduling makes the system run at high flow temperatures later, the tariff saving can be partly lost through worse efficiency.

Hot water matters too

If your heat pump heats a cylinder, hot water can be one of the easier loads to move into Cosy Hours. Many households can schedule the main cylinder heat during the morning or afternoon cheap window, then add a smaller top-up later if needed.

Legionella protection normally heats the cylinder to a higher temperature periodically. Where your controller allows it, schedule that cycle in a cheap period too. Check the heat-pump and cylinder guidance before changing safety settings.

Thermal mass helps, but do not overstate it

Homes with underfloor heating, concrete floors, solid internal walls or other useful thermal mass can often store heat through the peak period more comfortably. Radiator systems can still work, especially if the radiators were sized for low-temperature heating, but they usually feel more responsive and less storage-like than underfloor heating.

Lighter homes, exposed homes and homes with draughts may not coast as long. That does not automatically make Cosy unsuitable. It just means the best schedule may be gentler, with less forced peak avoidance and more attention on lowering heat loss.

Flow temperature may save more than tariff tweaking

Weather compensation adjusts the heat-pump flow temperature as the outside temperature changes. In mild weather, the system should be able to run cooler. In colder weather, it may need a higher flow temperature to keep the home comfortable.

This matters because lower flow temperatures usually improve heat-pump efficiency. A tariff schedule that saves a few peak units is less useful if the system then has to recover at a much higher flow temperature. If your bills look high, ask your installer to check the heating curve, radiator balancing and hot water settings before assuming Cosy is the problem.

How to estimate your own running cost

Avoid relying on a single national example. Instead, build a rough personal estimate:

1. Find your expected annual heat-pump electricity use from the installer’s design, your app or a full year of bills.
2. Estimate how much of that use can realistically sit in Cosy Hours, standard hours and the 16:00-19:00 peak.
3. Check your current regional Cosy prices in the Octopus app or the tariff comparison tool.
4. Compare that with another realistic tariff, not just with a headline unit rate.
5. Include standing charges, any remaining gas standing charge and whether you also have EV, solar or battery storage.

A heat pump using 4,000-6,000 kWh of electricity a year will not have the same bill in every home. A well-insulated house with low flow temperatures and most heating away from peak should look very different from a leaky house that needs frequent high-temperature recovery.

Comparing Cosy with gas

Gas comparisons need care. Gas is usually cheaper per kWh than electricity, but a heat pump uses fewer units of energy because it moves heat rather than creating it directly. A modern heat pump can deliver several units of heat for each unit of electricity, though the seasonal result depends on the installation.

If you remove gas entirely, you may also avoid a gas standing charge. If you keep gas for cooking, backup heating or another appliance, that saving may not apply. For many homes, Cosy should be judged as part of the full heating design rather than as a simple electricity-versus-gas unit-rate comparison.

When Cosy may not be the best fit

Cosy may be less attractive if:

• your heat pump cannot shift much load away from 16:00-19:00
• your home needs high flow temperatures for long periods
• hot water demand forces frequent top-ups outside cheap windows
• you have an EV and Intelligent Octopus Go would cover more useful overnight use
• you have solar, a battery or export needs that change the tariff calculation
• your smart meter cannot provide the half-hourly data Octopus needs

Octopus’s own smart-tariff guidance often points heat-pump-only homes towards Cosy, but mixed-technology homes need a fuller comparison. If you have a heat pump plus EV, solar or battery storage, compare the whole household rather than picking the tariff with the lowest heat-pump-sounding label.

Practical bottom line

Cosy works best when the house can warm steadily in the morning and afternoon cheap windows, avoid most 16:00-19:00 heating and stay comfortable without high-temperature recovery. The best first step is not to chase a perfect schedule. It is to check that the heat pump is commissioned well, the flow temperature is as low as comfort allows and hot water is not fighting the tariff.

If that all looks reasonable and Octopus suits the rest of your household, you can then decide whether Cosy, Intelligent Octopus Go, Agile or another tariff gives the better whole-home result.