Side-by-side comparison
| Electric storage | Gas storage | Continuous flow | Heat pump | |
|---|---|---|---|---|
| Up-front cost | Lowest | Moderate | Moderate | Highest |
| Running cost | Highest | Moderate | Moderate | Lowest |
| Space needed | Tank footprint | Tank + flue clearance | Compact wall unit | Tank + airflow clearance |
| Runs out of hot water? | Yes, then recovers | Yes, recovers faster | No, within flow rate | Yes, slower recovery |
| Needs gas | No | Yes | Yes | No |
| Needs power | Yes | Not always | Yes | Yes |
| Noise | Silent | Minimal | Minimal | Fan noise in operation |
Where each one genuinely fits
Electric storage
The default where there is no gas and the budget is tight, or where a straightforward like-for-like changeover is required quickly. On an off-peak tariff the running cost is more reasonable, provided the household's usage fits the heating window.
Gas storage
Suits households with concentrated peak demand and a gas connection. Recovery after heavy use is faster than electric, and in most cases the unit will keep working during a power outage.
Continuous flow gas
Good where plant space is limited or the household dislikes running out of hot water. The constraint is flow rate: two showers plus a tap will exceed a small unit's capacity, so it must be rated for how the home is actually used.
Heat pump
The lowest-running-cost option for all-electric homes, and a good match for rooftop solar when scheduled to run during the day. It needs an outdoor position with clearance and tolerance for fan noise, which rules it out on some compact blocks.
There is no single best system. The right answer is the one that fits your connection, your peak demand and the space you actually have.