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Octopus Cosy Heat Pump Owners & Discussion Thread

 
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Air Source Heat Pumps (ASHPs)
Last Post by swwils 3 months ago
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 AndrewJ
(@andrewj)
Reputable Member Member
Joined: 2 years ago
Posts: 259
Topic starter 16/05/2026 7:57 pm  

@swwils mine is mostly off now.  Hot water for an hour 02:30 to 03:30 then heating to 21c from 03:30 to 05:30 although in reality it will only come for a short period to bring the house temp back up to that temp.  This is giving overall COPs of <4 with the OAT in single figures right now, but a quick calc of the heating only COP from this morning gives 4.08 at 7.4c.

What would be very useful is if you could describe your system, in some detail: how you have it set up, how you run it, hub parameters etc.  

 



   
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 AgentGeorge
(@agentgeorge)
Reputable Member Member
Joined: 2 years ago
Posts: 194
17/05/2026 8:46 am  

@swwils there is no logic to oversizing a heat pump. It wastes energy keeping a large compressor and heat exchanger running.

you got the 9kW cosy as the smaller 6kW was not suitable for your properties heat loss

its not just the COP you look at, its the energy consumption in kWh per day.

My Cosy6 was running full operation the first winter as i hadn't completed the insulation in the new kitchen extension roof.

This winter period, the Cosy6 was much quieter, insulation makes a huge difference to heat loss. My rear extension is fully insulated, floors, ceiling, walls, to 150mm. It is always 2C warmer than the rest of the house

This Autumn, after the wall insulation is installed in the Lounge/Kitchen I will be rebalancing the UFH towards the Lounge



   
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 swwils
(@swwils)
Estimable Member Member
Joined: 1 year ago
Posts: 97
14/07/2026 6:38 pm  

Firmware updates have massively helped with my cosy vibration/noise it seems to not run the fan that fast anymore. So very pleased 👍

Octopus customer service also great once the gears got turning 



   
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 AndrewJ
(@andrewj)
Reputable Member Member
Joined: 2 years ago
Posts: 259
Topic starter 14/07/2026 7:25 pm  

Did you see the post on Facebook where an air conditioning module, plumbed into the wet circuit and powered by the Cosy was shown?  Only a prototype at the moment but it looks interesting.



   
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 swwils
(@swwils)
Estimable Member Member
Joined: 1 year ago
Posts: 97
14/07/2026 8:07 pm  

@andrewj I personally don't like domestic fan coils, people never clean the indoor units with cassettes let alone coils 



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 5561
15/07/2026 7:58 am  

Posted by: @swwils
↑

@andrewj I personally don't like domestic fan coils, people never clean the indoor units with cassettes let alone coils 

You are right that people don't clean things but, If they want cooling then they will have to get used to cleaning, it comes with the territory.  Either that or suffer the consequences.

 


This post was modified 3 months ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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 swwils
(@swwils)
Estimable Member Member
Joined: 1 year ago
Posts: 97
15/07/2026 8:08 am  

@jamespa haha very true, although the engineer yesterday said that condensation would occur at 30C flow temp somehow 😂



   
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