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Last seen: Jun 6, 2026
@jamespa That was my feeling, but I have seen it argued that oversizing does not cause significant inefficiency, so I erred on the diplomatic side 🙂
@johnnyb I believe the jury is hung as to whether an oversized heat pump is actually less efficient. I think most people though agree excessive cyclin...
@johnnyb Using the immersion wont improve the efficiency but if you can get cheap rate electricity it should be no more expensive and may even be chea...
@jamespa That's interesting James. Two other things occurred to me after my last post.The first is that all DHW cylinders include an immersion heater ...
The point about needing a legionella cycle at all and how hot the water needs to be if you use one. Its an interesting point that if people cannot a...
@johnmo absolutely agree. However I've had conversations with heating engineers who categorically take a different opinion 🙃
@johnmo That's fair enough. Although I'm not sure how that rule squares with having to use an immersion for legionella in addition to the heat pump.
Im not sure I follow why you are opposed to using an immersion heater for the very cold days? If the price using off peak energy works out to the same...
@johnnyb Hi. Yes I just use the immersion overnight. Although the heat pump could probably get a DHW COP of 3.5 as the price per unit is 3.5 x less ov...
@johnnyb I think potentially you may be right that 8kW will be too large for your heating although the 5kw may struggle with DHW. Can I ask if you...
@scalextrix When do you intend taking the plunge? Do you have next winter to work with to get some good data? If you have the house area and a feel ...
@scalextrix I think what you are describing is exactly why I am so sceptical of room by room assessments and more supportive of previous use estimates...
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