Octopus Cosy — The Heat Pump Tariff Reviewed
Cosy is built around a heat pump's daily rhythm. Two cheap windows — 4am–7am and 1pm–4pm — let you pre-heat the house when prices are low, then coast through the expensive 4pm–7pm peak with stored warmth. Done well, it's the cheapest way to run a heat pump in the UK.
In one sentence
Heat pump tariff with two off-peak windows. Cheapest UK option for low-flow-temp heating. Peak rate stings if you can't avoid 4pm–7pm.
What Octopus Cosy actually is
Octopus Cosy is a three-rate (time-of-use) electricity tariff with two cheap windows — 04:00 to 07:00 and 13:00 to 16:00 — and a high-cost peak from 16:00 to 19:00 every day.
It's designed to match how an efficient heat pump should run: pre-heat early morning while the cylinder warms, top up mid-afternoon before the peak, then ride out the expensive evening window on stored heat in the fabric and water.
Eligibility: you need a heat pump, a SMETS2 smart meter, and Octopus needs to verify the install. Customers without a heat pump are usually declined or pushed to Go/Agile.
Pros
- Two cheap windows totalling 6 hours per day — much more usable than Go's single 5-hour overnight window.
- Off-peak rate of ~13p/kWh is roughly half the price cap.
- Mid-afternoon window lines up perfectly with solar PV gaps in winter.
- Genuinely the cheapest tariff for running a UK heat pump if you have the controls.
- No exit fees.
Cons
- Peak rate of ~36p/kWh (4pm–7pm) is well above the cap — you must avoid using power then.
- Requires a heat pump — Octopus verifies before approving.
- Manual heating controls don't really work — you need a smart controller or you'll forget.
- Cooking dinner in the peak window costs 30–40% more than on the standard variable.
- Day rate (everything outside the three windows) is also higher than the cap.
Who Octopus Cosy suits
- Heat pump owners with a well-insulated home and a heat curve set up for low-flow-temp running.
- Households with a hot water cylinder that can be reheated in the off-peak windows.
- Anyone with thermal mass (solid floors, brick walls) that holds heat through the 3-hour peak.
- Smart heating controllers (Homely, Havenwise, Adia) that schedule based on Cosy rates.
Who should avoid it
- Homes without a heat pump — you can't sign up.
- Poorly insulated homes that lose heat fast through the peak window.
- Households that need a hot dinner cooked on the hob at 6pm every night and can't shift it.
- People not willing to set up a heating schedule — running 24/7 on Cosy is more expensive than the standard variable.
Current rates
Live rates pulled from the Octopus Energy public API for Octopus Cosy (COSY-FIX-12M-26-06-25). Standing charges and unit rates shown include VAT. Agile shows a 24h average; half-hourly prices vary throughout the day.
| Region | Unit rate | Standing charge |
|---|---|---|
| London | 33.37p/kWh | 44.12p/day |
| South East | 30.81p/kWh | 49.41p/day |
| North West | 30.53p/kWh | 46.63p/day |
| Scotland | 33.40p/kWh | 57.99p/day |
| Wales (South) | 30.34p/kWh | 56.56p/day |
Worked example: heat pump home, 6,000 kWh electricity/year
A 3-bed heat-pumped home uses 6,000 kWh/year (4,000 kWh for heating, 2,000 kWh other). On the Ofgem cap that's £1,620 in unit charges.
On Cosy with smart controls: 3,000 kWh in the off-peak windows at 13p (£390), 2,500 kWh during the day at 26p (£650), and just 500 kWh during the peak at 36p (£180). Total: £1,220 — a £400 saving.
On Cosy without smart controls (heat pump runs 24/7, cooking in the peak window): bill rises to £1,720, which is £100 more than the cap. The savings only materialise if heating is scheduled to avoid 4pm–7pm.
Work out your own numbers on Octopus Cosy
- Heating with electricity? Cost each heater per hour, day and year with the electric heating running cost calculator using this tariff's unit rate.
- Want to move appliances into the cheap window automatically? See our review of the Hive Active Plug for scheduling washing machines, heaters and dryers overnight.
- Charging an EV overnight? Compare this with the Octopus Go tariff review and its 00:30–05:30 off-peak window.
How to switch to Octopus Cosy
- Confirm you have a heat pump installed (Octopus will ask for make/model during signup).
- Confirm your SMETS2 smart meter is sending half-hourly readings.
- Apply at octopus.energy/cosy — Octopus may take 1–2 weeks to verify the heat pump install.
- Set up smart heating controls (Homely, Havenwise, or any controller that supports Cosy windows). Without these, savings are marginal.
- Schedule hot water reheats for the off-peak windows. Don't run an immersion in the peak.
- After 30 days, compare bills against the price cap. If you're not at least 15% under, your schedule needs work.
Independent review. PowerGuardian is not affiliated with Octopus Energy. Rates shown are indicative for Octopus Energy's Octopus Cosy tariff at the time of review — check the supplier's website for current pricing before signing up.
Frequently Asked Questions
Other Octopus tariffs
Octopus Go
5-hour off-peak window at ~8p/kWh for EV charging. Day rate slightly above the cap. Best for EV households.
Read reviewOctopus Agile
Half-hourly variable rate. Best for flexible households with a smart meter. Risky if you can't shift usage.
Read reviewOctopus Tracker
Single daily rate for gas and electricity. Cheaper than the cap most of the year, painful during winter wholesale spikes.
Read review