Keep the pipe run from the heat pump to the cylinder/UFH manifold as short as possible and don’t use mixing valve on the manifold. Obvious now but not at the time. Having said that, I’ve just seen a Thermal Earth install with heat pump at the bottom of the garden! 😁

@bontwoody The one thing I would change is that being a member of or certified by the MCS is absolutely no guarantee whatsoever of a installer’s competence. I feel that such certification should indicate that said installer really is competent to carry out the installation in such a way that the average customer arriving home from a ride on the No: 39 bus who knows diddly squat about technical matters relating to heat pumps and their installation could be confident that a high standard installation has been carried out on their behalf. Regards, Toodles.

Posted by: @bontwoody

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Keep the pipe run from the heat pump to the cylinder/UFH manifold as short as possible and don’t use mixing valve on the manifold. Obvious now but not at the time. Having said that, I’ve just seen a Thermal Earth install with heat pump at the bottom of the garden! 😁

I would like installers to balance system and work out curve with which lowest flow temp will keep house@21deg and not just go high flow temp to avoid call backs. At 0deg last winter i was running @43deg, thanks to this forum i am now running@29 even below zero.

• @newhouse87 just the unit being close to the manifold and cylinder. I mistakenly put my heat pump out of the way and had a long cold run. 

Ensure that the MCS installer was conversant programming the Samsung ASHP they recommended for 'optimal' use and not just rely on the factory default 'heat' and 'DHW' settings. I have since learned that there their best knowledge lies with Veissman and Vaillant. I have had to spend countless hours trying to research how to get the best out of the ASHP, what water law means and best settings for our property and system, etc, etc.

go forward in time to the point that a) good installers are widely available across all geographies - basically the mass of plumbing heating guys+girls have been trained up fully b) a reliable consensus has been reached with regard to best practice for system design, sizing and implementation c)  drag one of them back in time to do my system???

so I wouldn't have had to do it all myself....

in all seriousness I'd have gone 1 notch lower on sizing : 10-12 instead of 16, but only if one could be found that is designed as  "genuine 12", not a de-rated 16, with a suitable low downward modulation point . And focused more on the real world capabilities and behaviour of the units in-built controller. Those two might have led to a different manufacturer choice.

Posted by: @iancalderbank

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in all seriousness I'd have gone 1 notch lower on sizing : 10-12 instead of 16, but only if one could be found that is designed as  "genuine 12", not a de-rated 16, with a suitable low downward modulation point.

That’s really, because I’ve been mulling something similar in my mind about our system. I would, however, be very interested to hear your rationale on your thinking.

Posted by: @editor

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Posted by: @iancalderbank

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in all seriousness I'd have gone 1 notch lower on sizing : 10-12 instead of 16, but only if one could be found that is designed as  "genuine 12", not a de-rated 16, with a suitable low downward modulation point.

That’s really, because I’ve been mulling something similar in my mind about our system. I would, however, be very interested to hear your rationale on your thinking.

rationale pt1: I now know what the design condition heat loss of my house actually is. during the cold snap end of november we had -3C for quite long period. that proved beyond all doubt that my house needs about 9kw in those conditions. Not the 14 that maths suggested , which led me to buy a 16. If I add a bit of headroom onto the 9 to cope with defrosts, and to be able to reheat a 300L DHW tank quickly, I end up with a 10-11 . Obviously assuming its one where plated capacity is maintained at lower temps.

rational pt2: the other thing thats becoming more apparent from information that goes around this and other fora is that several of the 9-12 units are actually firmware de-rated 16s. the abiliity to modulate down is completely key to mild temp performance, and is based on what size it was in the first place, not what its been de-rated to. so it'd be pointless me buying a samsung 12. or a daikin 12.  Different brand needed who are better at designing for this mid size and better at modulating right down (have you noticed how  any new heat pump announcement on linkedin quickly turns into key individuals asking about this?) .  I expect the (rare as hens teeth) really good installers know which brands do this best already. heatpumpmonitor.org gives some significant clues.

Definitely a better understanding of the heat demand of my home. Before installation I tried reducing the output temperature of the boiler to simulate a low temp flow system, which was all fine, but in retrospect was not low enough and certainly not done in any kind of way that gave any useful knowledge, eg knowing the OAT as well! The EPC for this house suggested energy requirements way above than any of the previous annual gas usage figures, so having the installer/Mitsubishi generate a predicted SCOP based on those did not seem relevant. The heat loss surveys I managed to generated online produced lower figures than the detailed undertaken by the installers - but theirs is the one that counts and defined the size of heat pump selected.

Ironically, as a consequence of having a heat pump I now have the data that would make selecting a heat pump more accurate - the missing piece of the puzzle is how to use the existing characteristics of a building and its heating system to inform the heat loss calculation made just through guessing the construction fabrics. For example, I came across a 'rule of thumb' recently suggesting that dividing an annual gas usage by 2900 would give an indication of the size of heat pump required - and that is a figure that looks about right for my situation now.

From what I can see the heat loss calculation fails to take account of the home being 'infested with humans', who probably produce (along with their various gadgets and gizmo's) something like 10% of the required thermal energy on colder days, and a much higher percentage on milder days.

When solar gain is also thrown into the equation the size of heat pump could be reduced even further, but it must still be able to heat the home when there is little or no solar gain.

What we need is British Standard Weather. 😋