Heat pumps for radiator heating are no longer a rarity, but there are still many questions about which radiators will work effectively with this technology. Many people automatically think of underfloor heating, but under the right conditions radiant heat can be well matched to heat pump operation. The key is not the type of radiator per se, but the overall system design, the size of the heat emitting surface and the heating temperature used.
Why does the type of radiator matter for heat pump heating?
The heat pumps are most efficient when operating at low heating water flow temperatures. This typically means a range of 35-45 °C, which is different from the 60-70 °C typical of conventional radiator systems. At such lower temperatures, the heat dissipation of radiators depends significantly on the surface area and the way in which heat is transferred to the room air.
The larger the heating surface of the radiator, the lower the water temperature is sufficient to provide the desired amount of heat. Therefore, the radiant heat rate and the design of the radiator are particularly important considerations for heat pump radiator heating.
The most common types of radiators and their suitability for heat pumps
For an existing or planned radiator system, it is worth considering how well the radiator type can be combined with a with heat pump.
The cast iron radiators typically occur in older buildings. They have a relatively small active radiating surface. They require higher flow temperatures and therefore have limited suitability for efficient operation with a heat pump. However, they have the advantage of a large heat storage mass, which can provide more uniform heat dissipation if the system is properly configured.
The tubular radiatorwhich are most often found in bathrooms as towel dryers, also rely more on convection heat dissipation. Although aesthetically pleasing and practical, they are generally not able to provide sufficient heat output at low heating water temperatures, and therefore play a complementary role in a heat pump system.
The steel panel radiators already have much more favourable properties. Due to their large, flat heating surface, they have a higher radiant heat rate, so they can also deliver good performance at lower forward temperatures. They are therefore the most compatible solution for heat pump radiator heating in most existing radiator heating systems.
Low temperature radiators, also known as heat pump radiators, are specifically designed for such systems. They are made up of several large surface plates and special heat deflection elements that allow them to provide high heat dissipation with heating water up to 35-40 °C. These radiators are ideally suited to the operation of heat pumps, especially when the aim is to achieve uniform comfort and stable system operation.
What is a heat pump radiator and how is it different from a conventional radiator?
A heat pump radiator is not a separate technology, but a design with an increased heat dissipating surface and an optimised internal structure. This allows a higher proportion of heat to be radiated into the room, providing a comfortable feeling even at lower temperatures.
The advantage of such radiators is that they distribute heat more evenly, are less dependent on high water temperatures and work better with the heat pump's weather tracking control. This is particularly important for these systems where too high a flow temperature would significantly reduce the efficiency of the system.
What size radiator is needed for a heat pump?
One of the most important issues in radiant heat pump heating is proper sizing. For old buildings it is often particularly advantageous to oversize radiators. The larger surface area allows the heat pump to operate at lower temperatures while maintaining the same comfort level. This is particularly important if the building insulation is not up to date.
Can a heat pump work with existing conventional radiators?
In many cases yes. A heat pump for radiator heating may then be suitable, if the radiators are in good condition, have sufficient surface area and the heating system is hydraulically well adjusted. It is not always necessary to replace the radiator immediately, often just adjusting the system may be enough.
You should consider replacing a radiator if the system can only heat at a very high flow temperature, if the rooms are heated unevenly or if the heat pump switches on and off too often. In such cases, a fan coil, which can be installed in place of the radiator and can work efficiently with a heat pump, may be a good alternative.
Radiant heat pump heating in an old building
In old buildings, the heat loss of the building plays a key role, in addition to the radiators. Poorer insulation, old windows or large thermal bridges all increase the heat loss required. In such environments, the size and type of radiators are particularly important for the successful operation of the heat pump.
Optimisation of the system may involve revising the sizing of the radiators, fine-tuning the heating curve and hydraulic control. Together, these will ensure that the heat pump for radiator heating is stable, even and comfortable.
Summary
A heat pump is a good solution for radiator heating if the radiators are able to provide adequate heat output at lower heating water temperatures. Large surface area steel panel radiators and low temperature radiators designed specifically for heat pumps are best, but existing radiator systems can also work well under the right conditions. The key to success is always the careful design and set-up of the whole system.