Do Heat Pumps Heat Water?
Yes. Most heat pumps are designed to heat water (to run your central heating system) to 45-50°C and domestic hot water is used at 38-42°C. However, unlike a combi boiler, a domestic heat pump cannot produce hot water quick enough to provide an adequate flow of water to baths, taps, and showers.
Domestic Heat Pumps
Most domestic heat pumps are not designed to provide hot water and space heating simultaneously, with the demand for hot water taking priority. If you're looking to get hot water from your heat pump, efficient water storage is key. Let’s take a closer look at how it works.
Can Air Source Heat Pumps Be Used For Hot Water?
With the right setup, an air source heat pump can be used to provide domestic hot water for a home. However, as air source heat pumps extract and deliver heat over a longer period of time, hot water can’t be provided on demand and so the use of a hot water cylinder is typically required.
How Do You Get Hot Water From a Heat Pump?
Heat pumps provide hot water using the same basic principles they apply for space heating. Here’s a brief breakdown of the process:
Heat Extraction with Air Source Heat Pumps
An air-source heat pump water heater uses outdoor air to heat water for domestic hot water and space heating. It works like a refrigerator in reverse, moving heat from the air into a water tank. Air source heat pumps extract heat from the outdoor air, even in cold conditions. The heat is absorbed by a refrigerant in the heat pump's evaporator coil, causing the refrigerant to evaporate and turn into a gas.
Ground Source Heat Pumps (GSHPs)
Ground source heat pumps draw heat from the ground or a body of water, which typically maintains a more stable temperature than air. The heat is transferred to a refrigerant in a similar manner.
Heat Compression
The refrigerant gas is then compressed by the heat pump’s compressor, raising its temperature. This high-temperature gas carries a significant amount of thermal energy.
Heat Exchange
The hot refrigerant gas passes through a heat exchanger, transferring its heat to water. As it cools, the refrigerant condenses back into a liquid, ready to begin the cycle again.
Heat Pumps and Hot Water Storage
Since heat pumps are primarily designed for space heating, they often struggle to provide enough hot water simultaneously. The process of producing hot water is slower than the demand. A common solution is to store hot water in a cylinder until it is needed.
Care When Storing Hot Water
When storing water between 20°C and 45°C, precautions are necessary due to the risk of legionella bacteria, especially if the water remains in the cylinder for extended periods.
Air Source Heat Pump Hot Water Temperature
To prevent legionella, it is recommended to heat the water in the cylinder to 60°C for at least 30 minutes or 55°C for 5-6 hours. For safety and convenience, it is typically advised to set the cylinder thermostat to 60°C.
Heat Pumps and Hot Water Efficiency
The most straightforward way to achieve a water temperature of 60°C is by using an electric immersion heater, typically installed at the top of the hot water cylinder.
For optimal efficiency (unless you are opting for a hybrid system), the existing hot water cylinder may need to be replaced with one that has a larger coil capacity. This is because a heat pump delivers water at a lower temperature than a conventional boiler.
The larger coils provide a greater surface area, improving the transfer of heat from the coils to the water in the cylinder.
Different Types of Heat Pumps for Hot Water
Air-to-Water Heat Pumps
These are the most commonly used heat pumps for both space heating and domestic hot water production.
Ground-to-Water Heat Pumps
These pumps extract heat from the ground or water sources, offering high efficiency. However, they require a more complex installation process.
Dedicated Hot Water Heat Pumps
These pumps are specifically designed to provide domestic hot water and are typically installed in homes where space heating is not needed.
How Does an Air Source Heat Pump Work?
Air source heat pumps extract heat from the outside air and transfer it to a refrigerant. This refrigerant is then compressed, raising its temperature, and subsequently distributes the heat to your central heating system.
Benefits of Air Source Heat Pumps
- Lower Energy Bills:
Depending on the heating system being replaced, air source heat pumps can reduce your energy bills.
- Reduced Energy Consumption:
Unlike traditional boilers that rely on fossil fuels, heat pumps run on electricity. They are more than three times as efficient as gas or oil boilers, which significantly lowers energy usage.
- Improved Carbon Footprint:
By using ambient heat rather than burning fossil fuels, air source heat pumps help reduce CO₂ emissions and contribute to a smaller environmental impact.
Will I Save Money on My Energy Bills with an Air Source Heat Pump?
The cost-effectiveness of running a heat pump depends on several factors:
- Whether your radiators are appropriately sized for the system.
- The details of your electricity tariff.
- How the heat pump is controlled.
- The type of heating system you are replacing.
Currently, heat pumps might run slightly more expensively than modern gas or oil boilers because electricity tends to be around four times more expensive than gas or oil. However, thanks to their high efficiency, savings are expected to improve as electricity prices change over time. Moreover, if you’re replacing another type of heating system, you should see savings on your energy bills.
For example, the potential annual savings of installing a standard air source heat pump—including any recommended radiator upgrades—have been estimated for an average-sized, three-bedroom semi-detached home.
