Electric boiler or domestic hot water heat pump: what pays off?

'Our boiler in the cellar is twenty years old and runs on electricity. Should we simply replace it with a new one, or switch straight to a domestic hot water heat pump?' This question comes up often at the moment, especially from people whose heating still runs on oil, gas or wood and who prepare their hot water separately with an electric storage tank. On top of that are those who have a PV system on the roof and prefer to put their summer electricity into hot water rather than feeding it into the grid.

The short answer

Anyone who heats hot water directly with electricity pays for one kilowatt-hour of electricity for every kilowatt-hour of heat. A heat pump gets most of the heat from the environment and uses significantly less electricity to do so. In its guide (Ratgeber) to choosing a heating system, klimaaktiv, the federal climate protection initiative, therefore explicitly recommends a domestic hot water heat pump or a solar thermal system instead of an electric boiler. According to the guide, both save energy and running costs.

Whether the switch pays off for you, however, depends on how much hot water you need, where the appliance can be placed and what happens to your heating system over the next few years.

How much weight does hot water actually carry?

More than many people think. The klimaaktiv guide states that in unrenovated existing buildings, around 15 to 20 percent of heat goes towards hot water. In very well-insulated homes, such as low-energy or passive houses, the demand for hot water is roughly as high as for space heating. So the better insulated the house is, the more worthwhile it is to take a look at hot water preparation.

What a domestic hot water heat pump does differently

A domestic hot water heat pump is usually a storage cylinder with a small heat pump mounted on top. It takes heat from the air in the room where it stands, or from drawn-in outdoor air. This results in a few practical points:

• The room where it is installed cools down and becomes drier. In a boiler room, laundry room or cellar with waste heat, this is often even welcome. In a cold, unheated room, on the other hand, the appliance operates less efficiently.
• Space and height matter. The appliances are taller than a traditional wall-mounted boiler and need a bit of clearance around them. Measure up beforehand.
• It is audible. A quiet fan runs along with it. In the cellar this is rarely annoying, but next to a bedroom it is more so.
• Hygiene remains an issue. As with any cylinder, the water should get sufficiently hot on a regular basis. Get shown how the appliance regulates this.

And what if a space heating heat pump is being installed anyway?

Then the question is usually quickly answered. A heating heat pump generally takes care of hot water as well via its own storage cylinder. An additional appliance is only needed in special cases, such as when the bathroom is located far from the heating system. If you are planning a heating replacement in the next year or two, plan the hot water at the same time instead of buying a new electric boiler now.

PV electricity into the boiler: a good idea with limits

Many PV owners heat their boiler with their own surplus electricity in summer. This makes sense as long as the sun shines. klimaaktiv provides a vivid illustration: on an average December day, each kilowatt of PV capacity generates around one kilowatt-hour of electricity; in summer, about six times as much. In winter, self-generated electricity is therefore hardly enough, and the boiler is back to relying on expensive grid electricity.

A domestic hot water heat pump turns the same amount of PV electricity into multiples of hot water. This means your self-generated electricity lasts longer, even during the shoulder seasons. A solar thermal system, on the other hand, can take over hot water heating almost entirely during the summer half of the year, according to klimaaktiv.

What you can do specifically

• Estimate consumption. Check your electricity bill or use a sub-meter to see how much electricity the boiler uses per year. Only then can the savings be calculated accurately.
• Check installation location. Is there a room with a bit of waste heat and sufficient ceiling height?
• Factor in replacing the heating system. If you are switching to a heat pump in the foreseeable future, plan your heating and hot water together. Our calculator provides an initial cost estimate.
• Check public subsidies. Our subsidy manager shows you whether and how domestic hot water heat pumps or solar systems are supported by grants in your federal state.

Our first assessment

An electric boiler is cheap to buy, but in the long run it is the most expensive way to heat water. If a replacement is due anyway, a domestic hot water heat pump is the better choice for most homes, even more so with solar PV on the roof. If a space heating heat pump is coming soon, save yourself the temporary appliance and plan both together.

Want to know what fits your house? Submit your request for quotes, and we will connect you with installers in your area.