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Having installed heat pumps for over a decade, we have experienced a wide range of properties, with varying levels of insulation. However, we often encounter people who have been told that heat pumps either do not create enough hot water or can’t cope with the variable British weather. Both are untrue. In this post, we answer the question "At what temperature do heat pumps become ineffective?" and debunk common misconceptions about heat pumps.

We do not doubt that some heat pump owners have had problems with the output level of their system when it is -3oC outside and blowing a gale. This is almost always down to the selection of the cheapest equipment or a system poorly designed for the application. Both of these points could have been solved by having a quality installer design the system correctly. You have to use the right tool for the right job.

First, let’s address a misconception that heat pumps are ineffective at producing a sufficient volume of hot water.

Are heat pumps ineffective at producing enough hot water?

Whilst it is true that conventional boilers are capable of achieving higher temperatures for hot water, usually up to 80⁰C, you do not get that at the tap as it would scald. Instead, cold water is mixed into the flow to the hot tap giving you a maximum of 50⁰C. A heat pump is capable of achieving temperatures in the region of 55 -60⁰C without adversely affecting efficiency so we just mix in less cold water on its way to the tap. This does mean that we need to store a larger volume of hot water to make up for the lower storage temperature. If the property is on the large side, a higher temperature of hot water may need to be stored to account for heat loss through old pipework as it travels the length of the building. Fortunately, there are also high-temperature models that can output around 70⁰C if required.

A second common misconception regarding air source heat pumps is that they struggle to maintain efficiency in damp British weather.

Are air source heat pumps ineffective in damp weather?

Again, this is simply not true.

Designing an air source heat pump system for the kind of temperatures we get in the UK requires some planning and the use of performance charts from the manufacture. The rated output of a 3kW air source heat pump for example, will depend on the outside temperature. It will only be able to output 3kW when running under average conditions like 3oC. If the heat pump is required to output 3kW at -3 oC, we will need a bigger heat pump, probably around 5kW to ensure it gives you the heat required.

Throughout the UK and most of Europe heat pumps successfully heat all types of properties and other heating targets without any top-up from fossil fuels. If a system is correctly specified and installed a heat pump is a viable, low carbon, efficient option for providing heating and hot water services to your home or business.

If you would like to understand more about sizing heat pumps for your project, get in touch or call us on 01293 821 345.


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