Grant ASHP

Hi everyone, new to OEM but love seeing the community that has been created through open-source tech!

We had a Grant Aerona 3 10kW unit installed in March, our house is a 1960s detached beaut (not), and according to the EPC is 156sqm. We have wet UFH throughout - the energy consumption has increased quite significantly in the past month (double - ~20kWh/day for the entire house, but can’t see the breakdown of the ASHP within this).

I would like to monitor the heat pump - am interested in the COP too as I can’t seem to find it in the Grant system (it seems poor compared to other ASHPs interfaces I’ve seen online). Is monitoring the COP with OEM too difficult to retrofit? What does it involve? I’m happy to follow instructions but not sure I feel confident enough to do anything beyond that.

Thanks in advance for any guidance and sorry if I’ve missed any key details!

Hi! Welcome to the forum.

The first place to look is this OEM guide: Heat Pump Monitoring. You can find performance stats of another Grant Aerona 3 in a similar sized property at

20 kWh/day for the entire house seems quite reasonable, given the time of year. It would have been considerably higher for a gas boiler.

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Hello Chris
I also have a recently fitted a Grant heat pump and use the level 3 heat pump monitoring bundle purchased from the open energy monitor shop. The heat meter may fit between the flow meter that comes with the unit and the filter so should be easy to isolate then fix. If you are not comfortable doing that it would not take your installer long. You would probably be best to have an electrician put in your heat meter, you may get away with one meter as your pump is built in. The rest is pretty much plug and play and Glyn is very helpful should you have any problems.

Thanks, that’s really helpful Gavin. Our next-door neighbour is a retired electrician so I may ask him!

How have you found your Grant heat pump so far? Any tips or advice? In the past week I’ve been optimising the weather comp in this cold weather period - it’s further confirmed my comment about the interface in my original post, but fine otherwise.

Hello Chris,
You can follow how my heat pump is performing on, mine is currently the only Grant H.P.
I am looking forward to seeing how yours compares.
It is performing as hoped, my only frustration is I can’t get the night mode (quiet mode) nor the low tariff mode to work. I have wired in the external switching and the symbols display on the controller but nothing happens. The controller won’t let me go into the parameters to enable them. The unit is manufactured by Chofu in Japan and I think I may need to get my hands on one of their controllers.
Have you managed to get these settings to work?

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Don’t you have one of their controllers, but with a big Grant sticker on it telling you not to change its settings and then a Grant contoller next to it? That’s what I’ve seen posted on other forums.