Do you need a new hot water cylinder for a heat pump?

Why are heat-pump cylinders different?

Heat pumps normally heat water at lower temperatures than a traditional boiler.

A heat-pump cylinder usually has a larger heat-exchanger coil so it can transfer enough heat into the stored water at those lower temperatures.

That does not mean every existing cylinder is unusable.

What does the source interview say?

The installer’s view was that an existing cylinder will often still work, but possibly at lower system efficiency than a purpose-designed heat-pump cylinder.

The transcript gives an intended efficiency range of roughly 250% to 350% for an existing setup, but that figure is too context-dependent to use as a promise for a specific home.

The practical question is whether the cylinder can meet your hot-water demand without forcing the heat pump to run hotter or for much longer than necessary.

What other equipment might be needed?

A heat-pump system may include expansion vessels and other hydraulic components.

Some heat pumps have an expansion vessel built in. Others need external vessels. A deaerator can help remove air from the heating circuit but is not universally required.

Your installer should explain why each component is present rather than adding equipment by default.

Will my loft tank come out?

Possibly.

Some upgrades replace a traditional vented hot-water arrangement with an unvented cylinder, which can remove the need for a cold-water storage tank in the loft.

That depends on the existing plumbing and water pressure.

What should I do next?

Ask your installer to assess your existing cylinder before pricing a replacement. Request the reason for any proposed change, expected hot-water recovery time and the effect on system efficiency.

Sources

• Source interview with Heat Geek installer, cylinder and plant-room discussion.

Last checked: 24 September 2026