Air source heat pumps

You’ll need a place outside your home where a unit can be fitted to a wall or placed on the ground. It must have some space around it to allow a good flow of air.

There are two types of air source heat pumps: monobloc and split systems. A monobloc system has all the components in a single outdoor unit, with pipes carrying water to the central heating system and a hot water cylinder inside your home. A split system separates the components between indoor and outdoor units. Whether a monobloc or split system is right for you will depend on your budget and the space available.

Monobloc systems tend to be cheaper and quicker to install and don’t take up as much space in your home, although they are generally slightly less efficient than split systems. The efficiency gain from split systems comes from some of the heat transfer taking place inside the building where it is warmer, resulting in less heat being lost.

If you’re not limited by space inside your home, it may be worth the extra cost of installing a split system. Your installer should be able to talk you through your options and help you choose the design that works best for you.

The external unit for a heat pump is identical for both monobloc and split heat pumps. Noise is created by large fans moving air across the heat exchanger.

Unless the heat pump is working very hard (ie in cold weather or producing high temperature water), you can expect the noise to be a similar volume to a fridge, if you were standing within a couple of metres. You could easily hold a normal conversation next to it, without raising your voice. As it gets colder outside, this noise will increase while it’s operating, but should still allow you to hold a conversation easily, only raising your voice a little.

The inside unit for a split system only contains valves and pumps and makes very little noise at all.

Most homes in the UK use radiators or underfloor heating to circulate hot water.

If you don’t currently have radiators or underfloor heating, you will have to decide whether you’d like to install them. This is a great opportunity to make sure the system is optimised for a heat pump, resulting in lower running costs.

You can find more information about the impact of radiators and underfloor heating on your heat pump’s design here.

Don’t want or can’t install radiators or underfloor heating? An air-to-air heat pump could work for you.

A standard heat pump doesn’t provide hot water on demand like a combi boiler, so you will need a way of storing hot water for when you need it. The size of hot water cylinder required will depend on the amount of hot water that your household typically uses, but the cylinder can usually be fitted inside any cupboard that measures around 80x80cm.

If you don’t have space for a hot water cylinder, you still have options. Some hybrid systems are designed with the heat pump providing heating and a boiler providing hot water on demand. You could also consider installing a heat battery, which takes up less space than a hot water cylinder. Instantaneous hot water heaters are also available and can be installed under your kitchen sink to provide a smaller amount of hot water.