In terms of location I am situated in Perthshire on an elevated site exposed to the east where we "enjoy" the sort of climate that you describe. Long cold springs with late winter temperatures sub zero for extended periods. I have been delighted with the performance of my heat pump since installation in 2019. An Ecodan 13kw with new pipe work and K3 and K2 radiators retro fitted to 1990s single story timber frame house of 2000 square feet. The house is maintained at a comfortable 19 to 21C day time and 15C set back at night. Recovery time in the morning is about 90 minutes and the Mitsubishi weather compensation is working very well and is remarkably "smart" at anticipating changing temperatures outside and keeping the indoor temps level.

Hot water does not seem to be an issue for me although others may quibble, it is ample and perfectly hot on 50C with a 300 litre tank and helped by solar thermal can easily get to 60C plus with a wee bit of sunshine. It initially slashed my fuel bills from the LPG/solid mix previously but the outrageous electricity prices recently have pegged that back. But I am still saving on previous bills and no cutting, splitting and stacking logs and no emitted carbon!

Solar panels are an excellent addition to a heat pump for keeping the electricity costs down. If you are concerned about the hot water temperature you could also use a PV diverter like Eddi or an instantaneous thermostatic water heater to boost the temperature to what you desire.

A heat pump can easily heat hot water to higher temperatures - but the problem is that its far less efficient once you start going much over 50deg. We actually have ours set at 43deg - which is fine! Plenty of hot water and hot enough. Cranking it up a bit if we have high usage from visitors.

We are in the south but heat an ancient cottage (with modern extension) very successfully.

Definitely check the pump is designed/sized for weather compensation - to ensure maximum efficiency

Solar panels are useful but must be remembered most of the production is say May - Oct ... when the heating is off! But at least Octopus is paying fair export rates these days & hopefully OFGEM will force them all to pay something based on wholesale or real world prices in near future.  If installing solar ideally add batteries as well... Adds flexibility to how/when you use solar as well as import cheap night elec on some tariffs. And adds the ability for emergency power supply too!

So many things to think about and no single answer!

You will find some of the highest numbers of users of ASHPs are in Scandinavia... so should be no problem with Highlands weather.

Thanks for the above replies.

As I'm sure most on this forum will know, there is so much conflicting information out there, it is difficult to know what to do.

I have seen statistics that show a high uptake of ASHP's in Scandinavian countries, do they have better installers or checks before installation?

I will look at getting another quote from a few more installers and see what they recommend.

I think I have a PDF from the quote I received, would it be helpful to post it here so that more knowledgeable people can have a look over it?

Thanks again.

Just regarding hot water part of this discussion. I have a 300L UVC.  It can run at anything between 50C and 70C depending on what heat source has been heating it - the ASHP or the immersion. With immersion, I let it heat up to 70. With the ASHP only to 50.

I blend the output of this cylinder down to 45C using a whole-house blending valve (45C is its minimum output level).

45C to the taps is absolutely enough to feel like "proper hot water" when you are washing your hands or doing the washing up. And of course blends down further for showers, to 38 ish. you definitely don't need the temperature of the stored water to be hotter than 45 for it to feel hot at the taps. 43 may well be enough. anything over 50 if let through to the the taps will feel "too hot".

The only reasons you may need it to be hotter  than 50 are a) legionella b) to increase the effective volume . A 300L cylinder at 70C contains about the same amount of stored heat as a 450L at 50C (assuming incoming temp of 10C). which can then be blended down at output to give 50% more water at the desired end user temperature (vs the lower store temperature). So that can be a solution if you want to get away with a smaller cylinder, or reheat less often. But 70C is not for doing (in fact impossible) with heat pumps. heat it to 50 with the heat pump , then do 50 to 70 if it makes sense to, only with immersion and only cheap off peak or free PV.

on PV, obviously it depends on how much you can manage to fit, but there is some season overlap and it can make a good contribution. By late feb / early march, there's reasonable amounts of solar and still 2-3 months of heating season. I was experimenting with "charging my house" during april - setting a higher LWT on the ASHP and/or a higher internal target temp during cold sunny afternoons , as the input energy was basically free at that point. then not needing to run the ASHP in the evening. less efficient from a COP point of view but more efficient from an input energy source point of view.

@iancalderbank very much in agreement. On legionella .... I think all ASHPs have a programmable function to raise the temp (say) weekly to ensure there is no problem. So again, perfectly acceptable to have a relatively low tank temp as the "norm".

We have a 300l tank at 43 deg and never run out. But as mentioned we raise that a bit when we have visitors only to reduce chances of it running out. Even then we only raise to 50deg

Thanks for the replies so far.

Has anyone here got one of the Vaillant Arotherm models on here?

It has been suggested by on of the installers that have been round to have a look.

Hi there,

We have a Vaillant Arotherm. This is our second summer with it now and we love it.  

Any questions you have please feel free to fire them over. 

We are in the NE of Scotland and it works really well. 

atb

Drew

@drew-pa 

Hi,

How old is your property and what insulation does it have?

Do you have oversized radiators and do they heat your property sufficiently well in the winter?

Do you find that your water temperature is hot enough?

Thanks

@drew-pa can you take a photo of the compressor's label? I know it's not easy. Thanks

@lsld 

1, 2004 and insulation is as per that period. We haven’t upgraded anything. 

2, only a couple were upgraded.  Downstairs is UFH. low and slow methodology warms the house nicely.  

3,. Certainly is.  I think we have a water temp of 50c and it does everything we need. We use about 2 kWh a day to heat the hot water.  

hope this helps.