Octopus Heat Pump Cost Calculator
Compare your annual heat pump electricity cost on Octopus Cosy, Octopus Go, and the standard Ofgem cap. The smartest UK heat pump households save 25–35% per year on running costs by switching tariff.
Your home & tariff
Based on Cosy unit rates as of Oct 2025. Octopus updates rates quarterly — savings hold relative to Ofgem cap.
What is Octopus Cosy?
Octopus Cosy is a time-of-use electricity tariff designed specifically for households with heat pumps. It offers three rate tiers across the day:
| Window | Hours | Unit rate (Oct 2025) |
|---|---|---|
| Cheap (3 windows) | 4–7am, 1–4pm, 10pm–midnight | 12.20 p/kWh |
| Standard | Most other hours | 24.40 p/kWh |
| Peak (avoid) | 4–7pm | 32.50 p/kWh |
The trick is to set your heat pump controls to load up the home and hot water cylinder during cheap hours, then coast through peak hours. With a basic buffer tank, you can typically shift 60% of your heat pump electricity to cheap hours — that pulls your blended rate down to around 19 p/kWh, vs 26.35 p/kWh on the standard cap.
Cosy vs Go — which is better for heat pumps?
| Feature | Octopus Cosy | Octopus Go |
|---|---|---|
| Cheap window | 3 × 2-3 hour windows (9 hrs/day) | 1 overnight window (4-6 hrs) |
| Cheap rate | 12.20 p | 8.50 p |
| Standard rate | 24.40 p | 24.40 p |
| Peak rate | 32.50 p (4-7pm) | None |
| Best for | Heat pumps with basic buffer | EV + heat pump with huge buffer |
| Typical heat pump saving | £200-£300/yr | £100-£250/yr (HP only) |
Cosy is the default winner for most heat pump households. Go is only better if you also have an EV (which dominates overnight charging anyway) AND a 200+ litre buffer tank that can store enough heat for the full day.
How to maximise savings on Cosy
- Install a buffer tank (50-100L) — lets you generate heat during cheap windows and release it slowly
- Use a heat pump cylinder with ≥200L — pre-heat hot water during cheap hours
- Set up weather-compensated controls — most heat pump controllers can take Cosy timings as input
- Pre-warm the house before the 4-7pm peak window so the pump can rest
- Consider a home battery — 5kWh battery shifts your non-heating loads (oven, kettle) too
What if I'm not on Octopus?
Cosy and Go are Octopus-exclusive products in the UK as of 2026. Closest competitors:
- EDF GoElectric 35 — overnight cheap rate, similar to Go
- OVO Charge Anytime — EV-focused, OK for heat pump if you have a buffer
- British Gas Electric Driver — overnight, less competitive for HP-only households
If you're not on Octopus, switching is straightforward and free (about 3 weeks). You don't need a smart meter installed first — Octopus will arrange one as part of joining Cosy.