I must point out another couple of things. I did not mention “design temp” nor did I claim that the OPs house would be “warm within hours”. 

Rather I stated what happened in my situation. We had hot water, and heat coming out of the radiators, that evening after my ASHP was turned on at 6pm in -10 outdoor temperature.

Thats simply what happened, like it or not.

I think it’s best if all parties draw a line under this now. It’s no longer helping the original thread and actually is quite unedifying to anyone coming across it. 

Please just agree to disagree. Thanks. 

@marvinator80 - you keep on responding to points I haven't made. I have never told you how to run your system. All I have said was that your initial short  statement didn't make sense, unless there were other factors in play, which it turns out there were. Once you had revealed them, that should have been the end of it, but you - to coin a phrase - chose to have your hackles raised, right from the get go. So be it, it takes all sorts.

Your obsession focus on the OP misses the point that many others asking themselves 'should I or shouldn't I' will read this post, and I took the view that your statement was misleading (a view I can hold without malice) and warranted clarification. One of the minus points about heat pumps is that being steady Eddies means they generally can't rapidly heat a house from cold, a point that has come up many times. Indeed, it is one of the reasons for the run them 24/7 mantra. Your bald statement flew in the face of all that, which is why I questioned it.

The statement is the statement, end of. I as a reader (or any other reader for that matter) cannot be expected to divine all sorts of other information from various clues in scattered posts. In a way, your statement was a bit like that of a car salesman who tells you the vehicle he wants to sell you is capable of going very fast, but omits to tell you that you will need use two additional booster modules to get it to go that fast (which means £££, installation and/or running costs). I stand by my assertion that a statement that omits the need for booster modules is misleading. That is not the same as saying you set out to be misleading. You might have done so - perhaps believing you have a mission to save the planet by getting everyone to fit a heat pump, and what's a little brevity with the truth when the aim is to save the planet? Or you may simply, and just as plausibly, have just rattled off a few words without thinking whether there needed to be some clarification. I am sure we all make such mistakes from time to time. Perhaps I am doing so right now.

You haven't I note addressed the other two points I made, those being (a) plugging a Grant 'integrated' cylinder (at least be grateful for small mercies, at least Grant haven't called it a 'smart' cylinder, but that can only be a matter of time, and while I am at it, all cylinders are in effect integrated, so it is just marketing B$) that doesn't appear to be anything more than a standard pre-plumbed/wired cylinder but at the same time and of more concern appears to have an inadequate coil area for use with a heat pump (I've read the Grant promo pages, I haven't found anything that says how it gets by with an inadequate coil area - or perhaps they too have secret little helper/booster modules they don't mention) and (b) the mystery of the hot water cylinder that doesn't lose any heat.

Frankly, I am getting rather bored with all this, and am inclined to call it a day, but another anomaly has presented itself. Alongside the photo of the wood burner from which we now know we were supposed somehow to divine that it was in use at system start up, is what I take to be a photo of your heat pump. It has two fans, which leads me to believe it is a higher output model, and sure enough in another post you mention it is 13kW Grant Aerona, Yet earlier in this thread you also say your house, which you built yourself in 2016, meaning I presume good insulation, has a 'pretty low heat loss' (again, no numbers, but pretty low suggests I dunno less than 10kW, maybe much less, various figures have been bandied around). This suggests to me you might have an oversized heat pump, and that you may have accidentally or deliberately used the old fossil fuel heat source wheeze of installing an over-powered heat source to gain faster heat up times. Can you please comment on this? I'm asking because again I myself consider it is grist to the should I shouldn't I mill in particular (if I do get a heat pump, what size will it be?), and more broadly part of a general understanding of how heat pumps work, and thereby, in broad terms, should and shouldn't be used.             

Posted by: @bontwoody

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I think it’s best if all parties draw a line under this now. It’s no longer helping the original thread and actually is quite unedifying to anyone coming across it. 

Please just agree to disagree. Thanks. 

You are right, but unfortunately I have cross-posted. I am not sure why, because I am usually one to make a point of not pouring petrol on the flames. 

Calm down a bit Ray. I’m not required to post to any arbitrary standard set by you. I shared my experience, factually, and that’s that. There was no omission whatsoever. I had already shared that I had a wood burner and the idea that it would not being used during an ASHP install in January is fanciful at best.

The immersion system is part of the newly installed system. The idea that one wouldn’t use it is to heat water quickly when you haven’t had a shower for 2 days is also fanciful.

At no point did I say anything contrary to the fact that ASHPs take a bit of time to heat a house “from cold” whatever that is. I simply said we had hot water and heat output fairly quickly in our case. which is true. That’s all. This seemed to upset you for some reason and you implied that what I said could not be true, which is absurd.

as for running an ASHP 24/7, I have noticed no real difference from how I used to run my old boiler. I didn’t turn that off either, it simply produced when needed. Rather I control my heating systems and hot water as I need and they decide when the pump needs to work. 

I keep my underfloor heating at a particular temperature and when it has a heating the requirement the ASHP spins. when the radiators upstairs have a heating requirement, the ASHP spins. When hot water needs topped up, the ASHP spins. 

when temperatures are reached and exceeded by 0.5 degrees the pump stops. When the temperatures drop below the set temp by 0.5 the pump comes on again. 

if people want to set back overnight of whatever that is up to them. For the radiators I have noticed no difference at all from my oil boiler in terms of speed responsiveness. The radiators are larger and run hot or less hot depending on the outside conditions and weather comp.

Perhaps my pump, install and property aren’t exactly the same as yours, Ray.

@bontwoody ok.

Posted by: @marvinator80

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Perhaps my pump, install and property aren’t exactly the same as yours

You are correct, they aren't, mine is an old leaky building, yours is a modern build. I apologise if I came across as all fired up, I don't actually feel like that, though I do admit I can be a bit tenacious in making my point at times, for which, again, I apologise. Can I suggest that all that can usefully be said (and perhaps a bit more than needs to be said) has now been said, and we draw a line under this, as @bontwoody suggests?

Argument over and back purely to the points at hand. Ray, my heat pump isn’t oversized. The calculations were done by the installer and I don’t have them to hand but what I would say is that I have a fairly large house at 294sqm or 3165 square feet. 

The ASHP also serves the garage which is 66sqm down stairs and my office above it is 45sqm. So that’s 405 sqm total or 4360 square feet.

for the size of the property I queried whether it should really have been the 17KW version but the engineer was quite sure that 13KW was the best option due to the way the house has been built. Also the 13KW model of the Grant Aerona is more efficient than the 17KW.

@marvinator80 - OK, and I am glad it has all worked out well for you.

@cathoderay @marvinator80

Thank you both. 😁

@cathoderay apologies for my snark. I am a bit defensive about this stuff. It was a lot of work over the last 2 years researching and planning and getting the system set up as I had intended, including building the garage/office where the solar and battery is located.

I am pleased with the pump, solar and battery so far and it has worked out as I had intended but I am a bit weary. 

One other benefit we have had from changing from oil to ASHP has been noise. The noise of the oil boiler firing up could be heard in our bedroom at night. It didn’t wake me but it did wake my wife and that really annoyed her. 

the ASHP is not silent when it is running but nothing like the oil boiler was and with it being outside the house we don’t hear it at all.