Hot Water Cylinders for Heat Pumps: Frequently Asked Questions (FAQs)

Hot water cylinders for heat pumps are designed to store domestic hot water while working efficiently with the lower flow temperatures typically produced by an air source heat pump or ground source heat pump.

Although they perform the same basic function as a conventional hot water cylinder, a heat pump cylinder normally requires a larger or more efficient heat exchanger coil to transfer sufficient heat from the heat pump into the stored domestic hot water.

The FAQs below answer the most common questions about heat pump cylinders, cylinder sizing, heat exchanger coils, hot water temperatures, recovery times, immersion heaters, and installation requirements.

Heat Pump Hot Water Cylinder Basics

What is a hot water cylinder for a heat pump?

A hot water cylinder for a heat pump is a storage vessel specifically designed to produce and store domestic hot water using an air source heat pump, ground source heat pump or another low-temperature heat source.

The main difference is normally the heat exchanger. Heat pumps generally operate at lower primary water temperatures than traditional gas or oil boilers, so the cylinder needs a sufficiently large heat exchanger surface area to transfer heat efficiently into the domestic hot water.

Does a heat pump need a hot water cylinder?

Most heat pumps providing both space heating and domestic hot water require a method of storing hot water. In a typical UK installation, the storage method is a hot water cylinder.

Unlike a combi boiler, a conventional air source or ground source heat pump does not normally produce large quantities of instantaneous domestic hot water. Instead, it heats water stored within the cylinder so it is available when showers, baths, and taps are used. Energy Saving Trust also notes that standard heat pump systems normally require a means of storing hot water, usually a cylinder.

Common questions 

What is the difference between a heat pump cylinder and a normal hot water cylinder?

Hot Water Temperature and Recovery Questions