Underfloor heating is a great partner to an air source heat pump. The efficiency of an air source heat pump increases as the required flow temperature decreases. Put simply, this means that the cooler you can run the system, the less it costs to operate.
If properly designed and installed, underfloor heating can run at very low temperatures. This makes underfloor heating and air source heat pumps a perfect combination for UK households.
Underfloor heating systems have a larger heat emitter area, so compared to a traditional radiator, which might occupy one or two square metres on your wall, the underfloor heating has a very large heat exchange surface.
Let’s look at how heat emitters work in more detail…
Heat emitters are about the difference in temperature between the emitter itself and the desired room temperature. Therefore, if you have your heat emitter running at 60 degrees and you wish to keep the room at 20 degrees, a small radiator will do that job, albeit inefficiently. In this case, the system will be working very hard to keep the temperature so hot.
If you install a larger heat emitter (underfloor heating or oversized radiators), the system can be run as low as 30 degrees and you will still get the desired 20 degrees in the room. Due to the fact the system is working at lower temperatures, it is inherently more efficient.
Also read: Are air source heat pumps any good?
With the increased efficiency in mind, would it be wise to install underfloor heating throughout the whole property, on all levels and in all rooms? Well, this depends on the structure of the building itself. It also depends on the nature of project. Let’s explore this in more detail…
Generally, installing underfloor heating on ground floors is straightforward for new-builds and extensive renovations. It gets more challenging for upper floors, and it isn’t always the best solution for small-scale retrofit projects – which I will explore later.
In new build properties, the ground floor is typically constructed on an insulated concrete slab which is ideal for installing underfloor heating, which is then covered with a screed. However, with a suspended timber floor installing underfloor heating becomes more challenging. Screeded systems add significant weight so joists will need to be upgraded to take the additional load, adding cost.
Lighter overlay underfloor heating systems are an option, although they tend to be less efficient than a screeded system (more on this later). They don’t add any significant weight but overlay systems will add up to 50mm to the floor height.
Low-profile overlay systems are available, but the thinner pipes carry less water volume, and this reduces the amount of heat output compared to a screeded system. Furthermore, you will still need to add insulation as heat will be lost if you overlay an underfloor heating system onto a solid floor.
If we can liaise with the project’s architect and other stakeholders early in the process, these issues are simple to resolve. Each project is unique, so get in touch if you have questions.
Because of the challenges of installing underfloor heating in suspended floors, a common solution is to have underfloor heating on the ground floor and oversized radiators on the upper levels of the property. Standard-sized radiators are not compatible, as outlined in the introduction to this article, due to the small surface area requiring a hotter system flow temperature.
In most cases, the heat requirements for a bedroom will be less than other rooms, so radiators don’t need to oversized to the extent that they would for a living room, for example, and can be designed to operate at the same temperature as the underfloor heating on the ground floor.
Also read: Ground source vs. Air source heat pumps
Retrofitting underfloor heating to an existing property which isn’t undergoing a major renovation can be tricky; uninsulated solid ground floors are can’t take underfloor heating as heat will be lost into the ground, and joist size and ceiling heights may restrict options for suspended floors.
However, underfloor heating is not always necessary when installing an air source heat pump – oversized radiators can do the job perfectly well if designed properly.
It is impossible to cut corners and expect an underfloor heating system to work efficiently – if anybody tells you otherwise, you should be very cautious of their motivations. Because a radiator system can work just as well as underfloor heating if properly designed, it does not make sense to shoehorn underfloor heating into every project, as the consequences could be costly.
What are the overall benefits of installing underfloor heating for your air source heat pump?
First and foremost, underfloor heating can run cool which helps the system stay efficient and not overwork itself. Furthermore, the aesthetics of underfloor heating can be desirable as there are no radiator units positioned on internal walls, providing more wall space and flexibility for creative interior design and furniture arrangements.
For new-builds and large-scale renovations, installing underfloor heating with an air source heat pump usually makes sense. In terms of future-proofing for a more efficient and sustainable way of life, this is often the best option. However, it is not the only option.
If underfloor heating is done badly, it can be costly. For example, let’s say that one room has an overlay system whereas the rest has screeding. Due to the fact that you can’t get as much heat through an overlay, the whole system needs to run very hot to keep one room warm. As a result, you need to back down the other thermostats to balance the system. This would compromise the efficiency of the heating system as a whole, and render your heat pump less efficient.
If you would like to know more about whether your property and heat pump installation is suitable for underfloor heating, contact Smart Renewable Heat today. Our independent renewable heat experts are here to help.
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