Why heat pumps shouldn't be treated like boilers

For the full list of articles demystifying heat pumps click here

Heat pumps are different

Heat pumps work in a completely different way to boilers. A heat pump doesn’t burn anything.

Instead, a heat pump sucks and then pumps heat energy into the home from outside. It either gets this from the air outside (air source heat pumps), or from the ground (ground source heat pumps).

It can do this in any weather.

Although a heat pump isn't a gas boiler, it can make radiators pretty hot, a bit like a gas boiler if you really want it to.

A heat pump can also be used in the same on/off, twice‑a‑day heating routine like a boiler.

But, heat pumps find it very hard work to make radiators as hot as a boiler does. This means using heat punps to make radiators very hot is very expensive.

It doesn't make sense to use a heat pump like a boiler.

The opposite is true. Heat pumps are extremely efficient at producing warm (but still very usefully warm) water for radiators and other things like heating hot water tanks.

So rather than blasting radiators with very hot water for short periods, heat pump homes work best when radiators have warm water pumped through them most or all of the time during the heating season.

So we have two options to keep a home warm:

• Use a boiler to send occasional blasts of hot water round the radiators or

• Continuously send lower temperature water round the rads

Homes leak heat all the time

It is a simple physical fact that homes constantly lose heat in winter, such as through the walls, ceilings and draughts.

This suits heat pumps very well. To be efficient they like to run constantly, and continually replace the heat that never stops escaping.

A heat pump will only work as hard as it needs to do this. It will pump exactly the right amount of heat into a home to keep it at a constant temperature.

Heat goes out all the time...a heat pump will continually and efficiently pump heat back in to the home to replace it.

Think of a home as a leaking bucket. A heat pump is like a gentle flow from a water tap continually keeping the water level in the leaking bucket at the same height.

A properly designed and setup heat pump system gives you a home that:

• Has comfort 24/7

• Does not have daily temperature swings

• Has reduced condensation and mould issues

• Creates no air pollution

• Low running costs

Some modern boilers can do many of these things too, but will often lead to higher energy costs and will always create local air pollution.

Air pollution from gas boilers is a known contributor to lung conditions such as Asthma.

It just takes time to get used to the fact that heat pumps work in a different way: As a ’buckets worth’ of heat leaks out, a heat pump pumps will automatically pump a ‘buckets worth’ of heat back in.

High temperature heat pumps

NOTE: There are heat pumps that are specifically designed to produce very hot radiators and "behave" much more like boilers.

They are more complicated and more costly than normal heat pumps Overall they are not as efficient as regular heat pumps. They have their place, but they are not the best solution for most homes.

Next: Article 3: Why some heat pump stories are so awful (and some so brilliant)

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Mark Thompson

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