Congratulations!  Let us know how it goes.  How long is the job scheduled for?

@kev-m 

2-4 days! Fingers crossed!!! Have a lot of confidence in the installers. They do renewables only and are Grant Grade 1 or whatever the grade is installers.

downstairs is underfloor, 5 of our 7 radiators upstairs are being changed from K1 to K2. 

house is 7 years old, well insulated and heat loss of 9000 at 294sqm so the stars do seem to align on this installation - touch wood 🪵 

Good luck. From my experience here's the hit list for a Grant G1 installer:

1. Ensure the installers use the Grant controller that comes with the Aerona3 as the master thermostat and system controller. Fit it somewhere where it can control and it is accessible, main lounge, hallway, etc. Do not allow them to bury it away in the garage/plant room and connect some dumb on/off 3rd party Hive, Nest, Tado of other thermostat to it. They are not suitable for ASHP control despite Grant G1 installers routinely fitting them. The Chofu/Grant ASHP controller can do 7 day programmed CH and HW, quiet mode, low energy overnight tariff consumption, and all manner of clever things with the appropriate peripherals connected. It's a bit complicated for the user interface, but well worth the investment of time to get to know your way round. It's vastly superior to every other 3rd party CH and HW controller on the market.

2. Resist installation of a low loss header on the circuit unless one is needed for zoning UFH and radiators. If they fit a LLH, ensure they properly balance primary and secondary sides, a visual flow meter is required on each side! The pump in the ASHP unit will probably need to be set to lowest speed if a secondary circulating pump is installed. Lazy Grant commissioners tend to just throttle the flow valve down on the primary side, and leave the ASHP internal pump running at full speed against a mostly closed flow regulating valve. They need to set the dip switches on the ASHP to suit to design flow rate for your system design temperature.

3. Ensure all external pipework is insulated in external weather grade pipe insulation, it has a thick UV resistant skin on the outside & is 20mm thickness minimum. If they use cheap 13mm thick Armaflex foam rip it off and make them do it properly. You want almost no heat loss on the external flow and return pipes.

4. Fit the biggest rads you can get upstairs. K2s, even K3s. The UFH will accept a nice low water temperature, you want it as low as possible upstairs too. So big rads to operate at lowest possible supply temperature. You've only one common heat source that can be set to a common temperature.

5. Weather Compensation. Ensure it is enabled on commissioning and get the installers to show you how to access and adjust the main parameters to fine tune this. You need to know this info, you own the system, and getting it right (by trial and error to suit the property) is the biggest single factor for efficient ASHP and good CoP. Control heating using weather compensation and only use TRVs as room over-heat prevention devices.

6. Solar PV - nice one. 🙂 Solar diverter for your Grant cylinder immersion. Use the free energy to get free hot water in summer and you'll probably not need to bother switching the ASHP on for HW through the summer months.

Good stuff. The Chofu/Grant kit is all good quality, but the installers need a little reminding they are not installing a fired boiler in my experience! 😉

@allyfish thank you for that, very much indeed. Very comprehensive and I will follow it to the letter. 

the installers are very much speaking this language although they did talk about installing a hive!!!

with my solar package I am supposedly also getting an Eddi, but different contractor and they didn’t know at the time I was getting ASHP. 

is an Eddi now pointless? 

How exciting @marvinator80 – please keep us updated. Feel free to post update photos so that we can see the progress.

Exciting times. Will follow your updates for sure.  The Eddi that you talk about is the solar diverter that @allyfish is talking about.  

Posted by: @marvinator80

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@allyfish thank you for that, very much indeed. Very comprehensive and I will follow it to the letter. 

the installers are very much speaking this language although they did talk about installing a hive!!!

with my solar package I am supposedly also getting an Eddi, but different contractor and they didn’t know at the time I was getting ASHP. 

is an Eddi now pointless? 

I would certainly recommend having an Eddi power diverter installed, since it should provide much of your hot water needs from Spring through to Autumn, without the need to run your ASHP for much of the time during this period.

Amazing. Thank you guys, I am buzzing!

Will chronicle the process for you all! 😀

2 of the upstairs radiators they are leaving as K1 because they reckon they are superfluous and not really needed in the first place. 

I was kind of pleased with that because they could easily have just changed the lot and charged me for it. 

so there will be 6 K2s and a couple of K1’s which I could turn on I guess if they were ever needed. Upstairs is about 120 sqm and it does benefit from the heat rising from downstairs and also our living room wood burner’s flue goes through the upstairs hall and we get some heat from this louvre. 

I felt quite clever putting that in when we built the house in 2016, otherwise it would just have been behind the plasterboard.

Excellent idea @marvinator80 to have the lined flue not boxed in and to benefit from some heat upstairs. 🙂

Grant installed a Hive thermostat with my system, it's now set to demand heating 17hrs a day, we knock the ASHP off at 9:30pm and on at 4:30am. If it gets really cold we sometimes override this for 24hr heating. I have six programmable Hive TRVs on wet rads which provide some zone control for weekday/weekend occupancy. Office during weekdays, music room during weekends, etc. It's useful for space zone control, but as an ASHP controller, the Hive is useless, it switches the compressor and pumps on and off far too often, and the hysteresis is fixed at 0.1degC and cannot be adjusted. This cripples the CoP and is not good to equipment longevity. Weather compensation takes care of space heating, which sits nicely at 18-19degC after a lot of tweaking and trial and error.

The weather compensation is now set to a maximum of 42degC at 0degC outside, and minimum of 32degC at 20degC outside. Above 20degC the ASHP will be off. I'll probably need to tweak that for the summer months to avoid heating when it's not required. But I can simply switch the heating off manually in the summer season. 42degC max flow temperature is considerably lower than the design heating temperature of 50degC, but that benefits the efficiency. You seldom get the SCOP the manufacturers claim, and which is stated on the MCS estimate, so everything you can do to maximise efficiency is beneficial. I have 12 rads replaced on a system with 22 in total. Most K2s, and couple of K3s. Some rads had already been upgraded a couple of years back to K2s and were adequately sized. Surprising how effective they all are even with water through them at body heat 36-37degC.

I was at my in laws up in Stornoway over new year. They have an 10KW (I think) Mitsubishi ASHP and I was encouraged by just how hot the radiators were. The house was really warm and is an older construction with less insulation than mine.

One thing I still can’t quite get my head around is what happens when it hits -10 like it did recently and how the lower temperature compared to traditional boilers can do the hot water for baths and showers. does this mean I should have had the temperature on my oil boiler turned down from 65 to 45 or 50 all along?

The installers reckon 2 days for the removal and installation and a day or 2 to spend entirely on “balancing the system”. 

interesting times ahead.