Air-to-air heat pumps and hot water: what actually happens to your boiler

The full-removal rule

DRAFT — placeholder pending installer confirmation. The Boiler Upgrade Scheme (Ofgem BUS Guidance v5.1, July 2026) requires the existing fossil-fuel heating system to be fully removed as part of the installation. You can't keep the old boiler running alongside the new air-to-air heat pump.

That leaves one obvious question: if the boiler goes, what heats your hot water?

Why air-to-air doesn't heat water

DRAFT — placeholder pending installer confirmation. An air-to-air heat pump moves heat between the outside air and the air in your rooms. It has no water circuit, so it can't feed a hot-water cylinder or your taps.

Air-to-water heat pumps and ground-source systems do heat water — that's why they attract a larger grant. Air-to-air is a different unit.

The options installers use for hot water

DRAFT — placeholder pending installer confirmation. In practice, installers pair air-to-air with one of: a dedicated hot-water heat pump (a small cylinder unit), a direct electric cylinder, or an instantaneous electric water heater at the tap. Which one fits depends on your household size, your existing pipework, and the electrical supply.

What to ask in your survey

DRAFT — placeholder pending installer confirmation. Ask your installer to spell out: which hot-water option they're proposing, the running-cost estimate on your electricity tariff, where the new equipment goes, and how the old boiler and gas connection will be decommissioned.