Most people have combi-boilers and the size of the boiler required is often dictated by the need to heat hot water for baths and showers quickly rather than space heating. With heat pumps, you normally have a cylinder for hot water and it is the space heating requirement that dictates the size you need. So how big should it be? Hearsay tells me that even with boilers, sales-people love to sell you systems that are bigger than you need. My heat pump is oversized by at least 50%.
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My heat pump is much bigger than it needs to be. I have tried to make it less intrusive with some stick-on leaf patterns. Still, at least I have renewable heating :-) |
Oversizing does matter, both for boilers and heat pumps.
- Large systems cost more - not as much as you might expect, but still more.
- Running at small fractions of full capacity reduces efficiency (usually).
- Large systems are physically large and, in the case of heat pumps, have a greater impact on the landscape (see picture above).
In this post I discuss a very simple rule of thumb for heat pump size - thanks to Michael de Podesta - and some reasons it gives an underestimate in my case. Also I show you how to cross check your installer's estimate using the EPC certificate for your home. I wish I had done this!