Octopus Cosy vs Standard Tariff — Heat Pump UK 2026
The honest comparison: how much does Octopus Cosy actually save vs the standard Ofgem cap for a UK heat pump household? Real unit rates, blended cost, and the 3 cheap windows you need to use.
The unit rates compared (Oct 2025)
| Tariff | Off-peak | Standard | Peak | Std charge/day |
|---|---|---|---|---|
| Standard Ofgem cap | 26.35p flat 24/7 | 62p | ||
| Octopus Cosy | 12.20p (3 cheap windows) | 24.40p | 32.50p (4-7pm) | 54p |
| Octopus Go | 8.50p (midnight-5am) | 24.40p | — | 54p |
Cosy's 3 cheap windows
- 4:00-7:00 AM — pre-heat hot water cylinder + warm the house before morning
- 1:00-4:00 PM — top-up heat during the day, refresh cylinder
- 10:00 PM - 12:00 AM — final cylinder top-up for overnight
That's 9 hours per day at 12.20p — a massive 54% discount on the cap rate. The trick is shifting your heat pump's runtime into these windows.
The peak trap — 4:00 to 7:00 PM
Cosy charges 32.5p between 4pm and 7pm — about 35% higher than the cap. If you let your heat pump run flat-out at this time (because the house is cold), you'll wipe out a big chunk of the cheap-hour savings.
Solution: use weather compensation + smart scheduling to pre-heat the house to target temp by 3:45pm, then let it coast through 4-7pm. Most modern heat pump controllers handle this automatically once configured.
Real annual cost: 3-bed semi (95 m²)
| Scenario | Annual cost | vs Standard cap |
|---|---|---|
| Standard cap (no shifting) | £985 | baseline |
| Cosy, no load shifting (40% in cheap window) | £850 | −£135 |
| Cosy + buffer tank (60% in cheap) | £695 | −£290 |
| Cosy + battery (75% in cheap) | £605 | −£380 |
| Go (overnight only, 85% in cheap) | £565 | −£420 |
Who should switch to Cosy?
✓ Definitely switch if you have:
- Heat pump with smart thermostat / weather compensation
- Buffer tank (50-100L) — most important enabler
- Modern hot water cylinder (180L+)
- Heat pump controller that supports time-of-use scheduling
âš Consider carefully if:
- No buffer tank (savings drop to ~£135/yr only)
- Older heat pump controller without scheduling
- Predictable household pattern that fights cheap windows (always cold at 5pm)
✗ Stick with standard cap if:
- Gas-only heating household (Cosy is for heat pumps + EVs)
- Very small electric usage (standing charge eats savings)
- Run a home business with high daytime peak usage
How to switch to Octopus Cosy
- Sign up at octopus.energy/cosy
- Octopus arranges smart meter install if you don't have one (free, 2-3 weeks)
- Switch from your current Octopus tariff (or any provider — free, no exit fees)
- 3-week switching window — you'll be on Cosy by week 4-5
- Configure heat pump controller for time-of-use scheduling
- Monitor first month — adjust schedule based on actual usage data
Tips to maximise Cosy savings
- Install a buffer tank (£600-£1,200) — payback in 3-5 years from increased savings
- Larger hot water cylinder (250L+) — store more during cheap windows
- Pre-heat thermal mass — concrete floors hold heat for 4-6 hours after cheap window ends
- Weather compensation — modulates flow temperature down on milder days
- Pre-empt the peak — house target temp hit by 3:45pm, coast through 4-7pm
- Consider a home battery — shifts non-heating loads too (oven, kettle, lights)
Cosy vs Go for heat pumps
Cosy wins for most heat pump homes — three windows align with heating demand throughout the day. Go only wins if you also have an EV (charges overnight 12:30-5:30am) AND a 200L+ buffer tank to store enough overnight heat for the full day.