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New Daikin 11kW Altherma 3M install - is it working as it should?

 
Air Source Heat Pumps (ASHPs)
Last Post by Synthbuilder 3 months ago
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 Synthbuilder
(@synthbuilder)
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Joined: 4 months ago
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Topic starter 11/01/2026 5:16 pm   [#2728]
I had the system installed by Octopus in October last year and the recent cold snap here in the UK has made me slightly regret the move to a heat pump from an oil boiler. My house is a standard sized three bed detached bungalow built in 1974 in a relatively exposed position 650ft above sea level in Cumbria, UK. It had cavity wall insulation added about 15 years ago, and roof insulation is to current specifications. Octopus calculated the heat loss to be around 10kW at -3.7C.
 
The system is based around a Daikin Altherma 3M 11kW with 180l Daikin water cylinder. There were five radiator changes made within the house.
 
COP for space heating only: October (3.74), November (2.77), December (3.12), January (2.09).
COP for DHW only: October (1.84), November (1.58), December (1.83), January (1.31).
COP overall: October (3.44), November (2.65), December (3.01), January (2.04).
 
The January figures were taken up to the 10th January 2026. 
 
My two point heat curve is now set at 50C at -8C, 30C at 15C. I altered the curve in November to lower the LWT as the pump was switching on and off a lot which may account for the slight better COP in December. Early in January I discovered that the back up heater was kicking in at 0C and I have since changed the equilibrium temperature to -7C. I have also switched off the 'increase under 0C' mode which was also on by default.
 
My heating schedule was 24/7 at 21C with set back to 19C at night. However, during the recent cold weather (just below freezing) it was costing me in excess of 20GBP per day. I have since made the set back temperature much lower to effectively turn the pump off at night and during the Octopus Cosy tariff's 4pm to 7pm peak. This has kept the daily cost to around 15GBP per day.
 
I have a 14 panel solar system with 6.2kWh battery. I am charging the battery twice a day during Cosy's two 3 hour cheap periods.

This topic was modified 3 months ago by Synthbuilder

   
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Toodles
 Toodles
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11/01/2026 6:16 pm  

Perhaps you obtain a higher solar yield than we do with our 8.1 kWp array (21 panels in 4 separate locations on 3 roofs and in back garden but neither optimally orientated nor free of some shading) but at present, our best yield for a day in January has been 6 kWh.

Now as to the Daikin heat pump, we have an 8 kW Daikin EDLA08 monobloc without an internal heater and the system is controlled by a Homely smart controller - thus direct comparison is meaningless - nevertheless, for what it is worth, here are a few details.

December COP was 3.6 and so far January has been 2.6; we are enjoying a 24/7 comfort level of 22.5 deg. C throughout the 4 bedroomed semi detached 1930’s house with cavity wall insulation. under-floor Q-Bot insulation on ground floor (though not under the kitchen as this is solid floor) loft insulation is 300 mm. plus some boarding with old fibre glass insulation of ~ 100 mm. There are also Celotex type panels next to the roofing felt.

We are on OE’s Cosy, use 27 kWh’s of Powerwall storage and only use grid power during the 8 cheapest hours to recharge the battery. Our DHW is separate due to not having space for the MCS requirement of a mega size tank for 4 bedrooms! (We use a Sunamp Thermino for this job which can be grid or solar charged.)

Our total electricity charge for December (we do not have gas at all) was £161.82 including all those added charges to subsidise gas etc. (1,013.96 kWh.) The solar energy exported provided 32pence.! The rest of the 101.4 kWh we produced was used rather than being exported.

You have been going through some of the most expensive part of the year for heating as the minus temperatures really do ratchet up consumption on heat pumps - come March, the consumption should be much lower but I think I would be asking why the internal heater is set to come on so soon as this will be running at a COP of 1 and not helping your savings at all!

If there is anything else you wish to ask about, just say please. Regards, Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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Toodles
 Toodles
(@toodles)
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Posts: 2711
11/01/2026 6:37 pm  

I forgot to mention: Octopus measured our heat loss at 6.5 kWh though I don’t have any written details of the other parameters as this was just what the engineers told me at the time of survey and we didn’t have them carry out the installation in the end (very long story there!).

We live in the SE of England, on the side of a hill at 60 metres ASL. with the prevailing westerly wind hitting us square on. The house is 97 sq. metres according to the EPC we had carried out for Octopus (C 72), we have since replaced the aging double glazing throughout with triple glazing and other factors including solar, battery and heat pump hadn’t taken place at time of the assessment. Regards, Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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Toodles
 Toodles
(@toodles)
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13/01/2026 10:41 am  

@synthbuilder Further to the above…‘What a difference two days make, 22.5 little kW hours.’

(Sorry, I couldn’t resist the corny subtitle.)

Taking the performance figures for the 10th. and the 12th. January, I thought you might like to see the difference. COP (according to Daikin at least) was 2.5 and on the 12th., 4.1; the difference being less than half the consumption on the milder day. Please see the plots for OAT’s, defrosts and IAT’s etc. 39.8 kWh’s then when milder, dropping to 17.3 kWh’s. Our consumption may be a little higher than many as we keep the whole house at 22.5 degrees C 24/7. I hope this may help to set your mind at rest.Then things look brighter on a milder day. Regards, Toodles.

IMG 1466
IMG 1467

This post was modified 3 months ago by Toodles

Toodles, heats his home with cold draughts and cooks food with magnets.


   
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 Synthbuilder
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Topic starter 13/01/2026 3:35 pm  

@toodles Thank you for your input. As the days have gotten warmer, so has my acceptance for this technology. Yesterday, Daikin says that my heating COP was 3.64 and my whole house electricity consumption was just 27.11kWh at a cost of £5. I've also been playing further with my weather curve trying to get LWT as low as possible while keeping my heat pump on all day.

I have also purchased another 6kWH of batteries to double my storage capacity which should see me through the more expensive 4pm to 7pm peak electricity rate.



   
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