Need some advice? - 01293 821 345 - energy@iso.co.uk

Since heat pumps first became available in the UK, people have been concerned about the output temperature they can reach and want to know if a heat pump will work with their existing radiators. This short answer is yes, of course.

Many consultants we work with have a rather outdated view on the possibilities of a heat pump system. They have been told that you will need underfloor heating and a highly insulated home to make a heat pump work and pass on this opinion to home owners at every opportunity. Often this seems to be because they would rather sell you a fossil fuel boiler.

Traditional non-condensing fossil fuel heating systems are generally designed to run at 60-65°C. Anything hotter than that running through your radiators is likely to cause a burn risk. The heat pumps we work with are capable of outputting these kinds of temperatures, but the efficiency of a system generating higher temperatures will be lower than one running at around 40-45oC. We aim to install a heat pump so it will be run at the highest efficiency and also provide enough heat for your home. Fortunately, we can do both as we often find that the existing radiators in the house are oversized.

If you already have a fossil fuel boiler with radiators, you can perform a simple test to demonstrate how oversized your radiators are for a system running at 60oC. Turn the heating on full and open any radiator valves that may be turned down. Make sure any thermostats are turned all the way up and wait for a few hours. If the property gets too hot, which it will, then it stands to reason that you are putting too much heat into the building as your radiators are oversized for that flow temperature. We tend to find oversized radiators have been installed to avoid having to do the calculations to work out what size they should be and because it is better to be safe than sorry. If you are considering a heat pump, this plays to your advantage.

As the radiators are oversized for a high flow temperature, they are almost always the right size for a lower flow temperature. This fact coupled with a weather compensated heating controller means a heat pump can put a constant flow of the correct temperature for your house based on the outside air temperature. For example, on a warm spring day, your house may only need a constant flow temperature of 25oC to keep the house at the desired 19oC temperature. On a colder day, the system may run 40oC through the radiators constantly to keep the house at the desired 19oC temperature.

So yes, it is true a heat pump will work better at a lower temperature, but this is still perfectly adequate for your radiators to keep your house warm. Our Projects page on the website contains plenty of examples of where we have used existing radiators with a new heat pump system.

If you are interested in finding out how your existing radiators can be used for a heat pump, get in touch or call us on 01293 821 345.

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