@phil-i,

you are essentially asking, "should I get a free heat pump now or wait a bit longer and pay for it".   Although Grant ASHPs seem to be less expensive than other brands like Mitsubishi, they are a known manufacturer and I haven't heard anything to suggest they are inferior to other brands.  It's more important to get the design and installation right than choose a particular brand IMO.  If I were in your position I'd go for it.  

My EPC and energy use numbers are similar to yours. My supplier favoured Mitsubishi; I was borderline 11.2kW/14kW and ended up with a 14kW, which is more than enough for us.   

I don't know yet.  Let me explain...

I was in exactly the same situation 3 months ago - lead times on the Ecodan cylinders were out to 12 weeks and we couldn't wait.  So we went with the Grant 13kW. House is about half the size of yours, radiators, TRVs, oil boiler, Cambridgeshire.

The installer recommended the 10kW Grant but I went for the 13kW as it's double fan and supposedly quieter (and the actual spec sheet says they are respectively 10.5kW and 11.4kW at 55C, which is more realistic since we have radiators - so the 13kW isn't actually massively more powerful, although the flow rates are higher).  It remains to be seen how it copes in spring and autumn when only a little heat is required, but in winter it seems to be coping fine.

Now, the Grant heat pump seems to be a good unit.  It's made in Japan by a company called Chofu Seisakusho Co. Ltd - Grant buy them from a European distributor and rebrand them. From what I've seen of the unit and the documentation it seems to be good build quality.  I've been curating some documentation here - the Chofu installation manual, service manual, etc and marketing information from other countries.

The problem is that Grant is really an oil boiler company, and they want a heat pump to behave like a boiler, which it isn't.  My install is absolutely by the Grant book, the problem is that Grant took the perfectly good English installation instructions from Chofu, deleted lots of stuff (it should do cooling, which they don't admit to.  I enabled the cooling button, but can't really test it in winter), and added a relay box to interface it to UK on/off boiler controls.

The trouble is that on/off thermostats aren't good for heat pumps - my installer provided a Honeywell Lyric controller which does TPI.  TPI is a way that, by default, it looks at every 10 minute period and decides how much the boiler should be on. Result is that it turns the boiler on for say 3 minutes, then off for 7 minutes, repeatedly throughout the day.  You can set that back to 20 minutes, but can't turn off TPI. This is terrible for heat pump efficiency. With some great help from a heating engineer who installs these, we managed to reverse engineer the Modbus protocol, which is a way of logging data from the heat pump, and I'm now logging this into Home Assistant.  That shows me how spiky things are:

I have, just today, figured out how to revert to the Chofu room controller (ie cutting out the Honeywell and using the heat pump's own room thermostat) and am doing some experiments as to what difference it makes. Removing the Honeywell out of the loop completely is going to require some minor rewiring of pumps and valves, but I have just tried things temporarily as a test for now.  I should get a better feel over the coming days.

We also have some noise issues which might be being caused by TPI's constant switching on and off, or might be something else (there was terrible noise to begin with, because there was loads of air in the system). The heat pump is currently mounted next to the kitchen, so about a metre from the kettle with a window adjacent, which means it is audible inside. A family member is very noise sensitive so the contingency plan is to move it to the bottom of the garden, if my tinkering can't improve matters.  From measurement the noise is in spec, but there are certain points in the spinup curve where it buzzes (another thing to investigate).

Another thing is that Grant have switched from installing a buffer tank (that we have) to a low loss header.  I'm sure some more plumbing-knowledgeable folks can comment on this, but I know plumbers familiar with the units are not impressed (read the Twitter replies) - I defer to more experienced folks, but seems to be just another thing Grant doing backwards to make it look like a boiler.

One other thing is that the way Grant plumb in the buffer isn't good for doing cooling - it should work, but be less efficient.  Investigating that is for another time of year...

The Honeywell does have the ability to be controlled by an app, the Chofu natively doesn't*. Since I have Modbus up and running on Home Assistant I'm thinking of doing something in that area too, not sure quite what. I gather some of the other heat pump vendors are better in this respect.

* Chofu the company also sells oil boilers and those can have controllers with apps which look very similar to the ASHP controller - maybe they will talk to it? But they would probably be in Japanese...

On the flip side, it works, it heats, the hot water is great.  On a cold January day (daytime maybe 3-5C) we're probably using 30kWh per day for heating, on a warmer one a lot less.

So I think you can get a better outcome if you can avoid some of the installation problems (buffer not LLH, use the room controller or put in a smart thermostat that will run the heat pump for long periods not pulse it), use the heat pump to control the pumps and valves rather than the thermostat.  I understand the price wholesale is quite good, which might be why installers like them.

According to the Grant person on that Twitter thread:

We are more than happy to let installers like yourself install how you want to and to get the best out of the systems they install. In fact we have embraced many more installers with our new offerings which include 3 port direct systems using our controller to maximise efficiency

Just to be clear - you Don’t have to fit the units this way. If you are an experienced engineer and are sizing systems correctly we have no issues with you fitting it to your preferred suitable method.

so it is something they are happy with, but your regular plumbing and heating engineer is going to install it like a boiler, and that's not so good.  It works and all, but it could be better.

Bottom line: would I do it again?  Depends how much money is at stake.  In our case we didn't have a lot of other options (the oil boiler had been condemned a year before and finally expired a few weeks before installation), and I think I probably would. Basically it was a calculated gamble, with various things I didn't know (noise, controls, cooling enablement) but thought were worth the risk, and some within my competence to address. I don't have final answers on those yet, but they are looking promising - I don't think there's any showstoppers.  (In the worst case, moving it will be most work, but we get to rearrange the garden which needs doing anyway). On the other hand it has become a bit of a 'project' - if somebody was offering me an Ecodan for a few hundred quid more I probably would still take it (although it's possible noise etc issues would still apply)

I'll be posting to this forum when I have some more progress on my experiments, but in the meantime I'm happy to try to answer any questions that I can.

• Great information @Prunus.

We have a Grant Aerona 13kW and are very happy with it. We are in Warwickshire. It is very quiet. We have it attached to the end wall of our extension and you can hear it in that room but it is about the level of fridge noise. 

We had it fitted as per Grant guidelines so have a buffer tank and Hive thermostat. We have it set to 19.5 in the day and 18 at night and it copes very well. It is using weather compensation.

We have had it 15 months and have had no problems. The first winter it struggled on a couple of really cold days but after it was serviced this year and some adjustments were made (I don't know what) it has been great. 

We monitor our electricity use but cannot split it between heat pump and general use. This week we have averaged about 41KWh per day for all electricity.

I hope this reassures you.

@phil-i, there's some good information above. I will add that the few people I've interacted with that have Grant ASHPs, they've all had very good support from Grant UK directly. From what I've heard, Mitsubishi, as the manufacturer, are not very helpful and they regularly have parts and/or heat pumps that are out of stock.

We've had a Grant pump for 5 years and, as followers of this site will know, have experienced some issues.

However I think we've identified that these are primarily due to the design and installation of our central heating, rather than the pump itself.

We do have a Honeywell timer that switches the system between space and water heating. This is per the Grant manual but I'm told by a number of contributors to this site that it is an outdated way of operating.

For maintenance I've used 2 different local firms who are on Grant's list of approved contractors. I didn't think either really understood heat pumps or underfloor heating. Many of Grants contractors, like so many in the industry, mostly do work on traditional boilers. For the future I will be booking a service engineer direct from Grant. When we had major problems with electricity usage in cold weather last year Grant did (after seeing commentary on this site) send an engineer around, gratis, to check the pump and re-configure some settings.

I, too cannot separate out the heat pump's electricity usage from the house as a whole. But the pump clearly accounts for most of the daily variation in kWh, depending on the outside air temperature. It sky rockets when this drops to 1 deg or below. I record daily electricity readings and this February is proving to be far better than last, but the weather is mild.

In the 12 months to the end of January we used 25% less electricity than in the previous 12 months. But I am still tinkering with weather compensation settings to see if I can find further savings. They are of course a drop in the ocean compared with the tariff increases.

Mike

@Prunus 

Having a Grant Aerona 10kW installed next week.

Really interested in your experience with the 13kW unit - have you been able to modify the flow temp based on room temperature?

@ggw have you had your Grant Aerona 10kW installed? Was it able to cope during the cold weather in December?

Hi @kitkad, I have a Grant Aerona 10kW installed since Oct last year. It struggled a little in the December cold snap, mainly due to the time it was spending defrosting. Most ASHP owners found the same thing. Doesn't matter which manufacturer or model. I have a 5kW log burner as supplementary heating, and it was able to boost the house temperature when the ASHP was 'saw-toothing' - slowly creeping up the water supply temperature before going it to defrost and it dropping back.

Grant claim the 10kW Aerona is a 11.1kW heating capacity unit and CoP 5.28 when tested to BS EN 14511 at 7degC air and 35degC water:

That's contrary to the original equipment manufacturer's (OEM) performance data, Chofu, who claim it is 10kW and CoP 4.39 at the same A7/W35 conditions:

I don't know how the EN 14511 test method can magically improve the performance of the unit by 10% whilst also improving the CoP by 20% above that declared by the OEM. Well, not unless someone is being creative in the Grant test department. Grant published data shows improved performance for the 6/10/13 & 17kW models over that declared by the OEM. It's amazing what a 'Grant' badge can do to the exact same unit! I would think that Chofu's data is more credible. Japanese manufacturer's data is generally factual and reliable.

It's a good unit, with reasonable if not class leading CoP. It can modulate down to 20-25%. Accurate heat calcs are the only way to ensure a ASHP unit is adequately sized. Resist temptation to oversize, because a larger unit than necessary may end up cycling on and off more frequently, rather than modulating if it spends a significant amount of time on part loads lower than the minimum turn down. A correctly sized ASHP should spend the vast majority of the heating season on part load not running flat out due to being too small and not cycling on and off due to being too large.

@prunus Thanks so much for this detailed discussion. I am having a Grant Aerona 3 (10 or 13kW) installed and was wondering about this aspect:

‘I have, just today, figured out how to revert to the Chofu room controller (ie cutting out the Honeywell and using the heat pump's own room thermostat) and am doing some experiments as to what difference it makes. Removing the Honeywell out of the loop completely is going to require some minor rewiring of pumps and valves, but I have just tried things temporarily as a test for now. 

Could you say a little but more on how to achieve this? Especially because Grant has disabled the useful buttons that are discussed in the chofu manual (ie detailed heating schedules economy mode etc) that I want to use to optimise with a ToU tariff like Cosy Octopus. 

Thanks to everyone on this forum, I feel much more empowered to really save on my energy use with an ASHP. 

@fjj 

I have done the same and fitted the controller in my main living area in the kitchen.

It may not stay there forever, but it is a good job - im currently running at a fixed 30Deg flow temp 24/7 (drying out a new build, slowly)

The weather aint playing ball at all - i'd say my costs are £10 per day currently - but windows are open and alike. its not a fair use comparison.

Does the grant controller aid in the ASHP ramping down? - I cannot see that it does.

Ive every room zoned for UFH but its all on bypass currently.