ReedRichards

Given that your heat pump is off anyway, you could make absolutely sure it is off by cutting its power and see if that makes any difference. Are you sure that the cleaner does not come early?

You didn't mention the E7 part first timer around. Having Economy 7, or a similar Electric Vehicle charging tariff, can really skew the normal economics of operating a heat pump. You can have a gas boiler that does WC and nobody objects if your heating system also has zones. Weather Compensation doesn't have to be as "hard core" as the Heat Geeks and their ilk would like it to be. When you start to sacrifice comfort for the sake of a bit more cost saving, where do you draw the line? Why not go the whole hog, put on your outdoor clothes and turn off the heating?

Weather Compensation is never necessary but it ought to save you money, surely? And it's certainly a complication because you need to work out how to set your water temperature based on what the outside temperature is. Bit just because @JohnMo didn't manage to do that doesn't mean that you won't. Weather Compensation works fine for me.

Isn't a combination of radiators and UFH simply the wrong thing to do? You are almost certainly going to need a higher flow temperature for the radiators so you don't get any economic benefit from the UFH. If you like UFH then install it throughout and save on running costs.

Surely the worst case scenario is that you use a fan heater to heat up the room quickly whilst the heat pump is providing background heating? But then why is the room colder in the first place if you have asked the heating to maintain a constant temperature? To me the central issue is whether the heating for the rooms housing the older person is compatible with the heating you want for the rest of the house. I like it cooler at night so I set back my heating. If I wanted part of the house at a constant temperature 24/7 then I would have to make that a separate zone. Hard core ASHP enthusiasts abhor zones because they tend to make running the ASHP a bit more expensive. So you pay a bit more to keep an old person comfortable; is that so terrible?

Then it seems ridiculous to get picky about the noise made by a heat pump; get the LPA to worry about the noise made by the planes. Long long ago I lived in Ealing and my building very occasionally found itself on the flight path of the planes going into Heathrow. You could not hear anything else at all when a plane was passing overhead.

So "near Stansted Airport" but not under the flight path?

I think somewhere back here is a post that says that the current Therma V generation controller does not work with the previous generation heat pump. Better check how long this ex-display model was on display.

That lack of modulation is not very good. if you need 4 kW output at, say, -5 C outside then you need 2 kW output at 8 C (assuming 21 C room temperature) and less than 2 kW at any higher outside temperature.

The most convincing argument for a buffer tank is if your warranty requires you to have one. My warranty obliges me to have a buffer tank. As someone who had his entire heat pump replaced under warranty after 3 years of service, I would caution against doing something that might void the warranty.

"Water Law" seems to be what is generally called "Weather Compensation" in the UK. Weather Compensation is unaffected by room temperature. But there is also "Load Compensation" where the heat source will work harder the further away the actual room temperature is from the desired room temperature set on the room thermostat. Load Compensation works very well maintaining a constant room temperature but it could reduce your heat pump efficiency by making it work harder when the room temperature needs to be increased rapidly. On the other hand, getting a room up to temperature quickly will boost your comfort so its swings and roundabouts.

Or you could conclude that it is allowing Octopus to install heat pumps for very little money, possibly for free.

I would have thought that "minimum load" would mean the lowest power that the heat pump could draw. I'm not sure about "minimum output". You're likely to be running at minimum load when it's relatively warm out so you could b achieving quite a high COP, so a decent output as a multiple of the load. Conversely, if it's very cold out the load will be high but the output might not be that much higher because the COP would be low. So I'm not sure when you would encounter a situation of minimum output.

The maximum output of your heat pump would seem to be way more than you need but the parameter you need to worry about is the minimum output. The higher the minimum output the more time your heat pump will spend cycling between on and off. That's likely to be less efficient than if your heat pump is on continuously heating you water to a lower temperature.

I think that is it, essentially. But if the calculations are done rigorously then if you spend, say, 90 minutes per day heating your hot water then that leaves 22.5 hours to heat your dwelling and that might just tip you over the edge into needing a bigger heat pump than if it took 45 minutes a day to heat your hot water, leaving 23.25 hours for space heating. Or it might make no difference whatsoever.