THE HONEST COMPARISON · AS OF AUGUST 2026
Two systems with different tasks
A domestic hot water heat pump uses additional heat from room or exhaust air and can therefore provide more than one kilowatt-hour of heat from one kilowatt-hour of electricity.
An immersion heater converts electricity directly into heat. With a suitable surplus control system, it can utilize available solar power in the existing storage tank. Both systems therefore fulfill different tasks and can complement each other depending on the installation.
THE OPERATING PRINCIPLE
Both solutions in 60 seconds
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01
The immersion heater
The immersion heater is installed in a suitable hot water or buffer storage tank. The heating element converts electrical energy directly into heat. An excess power controller can adjust the output to the currently available solar power.
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02
The domestic hot water heat pump
The domestic hot water heat pump extracts heat from the environment and transfers it to the potable water. A classic domestic hot water heat pump is designed for water heating and does not typically handle space heating. For installation, it requires sufficient space and suitable air ducting.
Efficiency is not the only question
1.
For the same amount of heat, a domestic hot water heat pump normally requires less electricity than an immersion heater. With a PV system, however, the system perspective also counts: a compatible immersion heater can utilize surplus electricity in the tank without completely replacing the existing hot water system.
Acquisition, installation, and operation in comparison
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01
Acquisition
Immersion heater: often uses an existing compatible storage tank and requires comparatively little additional equipment.
Domestic hot water heat pump: is technically more complex and operates with a compressor and refrigeration circuit. Depending on the design, it includes its own storage tank and corresponding air ducting as part of the system. The initial investment is therefore usually higher.
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02
Installation
Immersion heater: requires a suitable installation opening, sufficient immersion depth, and an appropriate power supply.
Domestic hot water heat pump: needs additional installation space, sufficient air volume, and, if applicable, supply or exhaust air ducts.
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03
Maintenance and operation
Immersion heater: operates without a compressor or refrigeration circuit. Deposits and conditions within the storage tank can affect operation and maintenance requirements depending on the system.
Domestic hot water heat pump: requires less electricity per unit of heat generated, but has more technical components and generates operational noise.
THE DECISION
Three questions lead to the right solution
Three points are sufficient for an initial assessment.
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01
Is there any surplus solar power available?
Regular surplus solar power may indicate the suitability of a controllable immersion heater. The economic viability also depends on the feed-in tariff, previous heating costs, and the actual amount of usable surplus.
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02
Is there already a storage system in place?
A suitable storage tank with an appropriate installation opening makes retrofitting easier. If the domestic hot water system needs to be completely replaced anyway, a domestic hot water heat pump may be the more comprehensive solution.
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03
How much renovation is possible?
An immersion heater can usually be added to a compatible storage tank with minimal modification. A domestic hot water heat pump requires more space but can independently handle hot water production.
Combine immersion heater and heat pump
1.
Both systems can complement each other: the domestic hot water heat pump handles regular water heating, while an immersion heater can utilize additional surplus solar power in the storage tank. This requires the storage tank, installation position, temperature control, and management system to be technically compatible.
Which solution fits which situation?
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Check immersion heater
With compatible storage, regular surplus solar power, and as little retrofitting as possible.
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Check heat pump
For independent, regular water heating with lower power consumption.
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Check combination
When the heat pump handles the base load and the immersion heater uses the additional surplus.
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Check attachment first
In cases of low surplus, unsuitable storage, or unclear installation conditions, have it professionally inspected first.
FREQUENTLY ASKED QUESTIONS
Immersion heater or domestic hot water heat pump?
Is an immersion heater inefficient?
An immersion heater converts electricity almost entirely into heat. A heat pump provides additional environmental heat from the same amount of electricity and therefore requires less electricity for the same amount of heat. An immersion heater can nevertheless be useful if it mainly utilizes existing surplus solar power.
Can I combine an immersion heater and a heat pump?
Yes, in principle. The domestic hot water heat pump can handle regular hot water heating, while the immersion heater uses surplus solar power in the tank. The tank, installation position, and control system must be compatible for this purpose.
Which is more cost-effective to operate?
That does not depend solely on the efficiency. The decisive factors are the electricity price, feed-in tariff, investment, maintenance, existing storage, and the available amount of surplus solar power.
NEXT STEP
Which solution suits your home?
First, check surplus solar power, battery storage, space, and the installation situation. In case of uncertainty, the storage manufacturer or a specialist company should confirm technical compatibility.
