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Cosy home (?)

 
Air Source Heat Pumps (ASHPs)
Last Post by JamesPa 3 weeks ago
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 alastair
(@alastair)
Estimable Member Member
Joined: 4 years ago
Posts: 36
Topic starter 25/11/2025 5:21 pm  

Hello all

We've lived with our Daikin 14kW Altherma monoblock since Feb 2022 and it heats the house pretty reasonably. I'd never say that the house is cosy though - the main bedroom and living room can be, but the rest of the house isn't. When we had the heat loss survey done and the system installed we were told to upsize all our radiators apart from two, which we did. We are now thinking of upgrading one of the radiators and adding a second bigger radiator two one of the rooms (we can't do a replacement for the rad in that room for various reasons). 

I don't think changing the heat emitters on the system should affect the efficacy of the heat pump but I wanted to post here to make sure that we're not about to make some horrendous error. Let me know if this is a bad idea 🙂

We've also done all the draught proofing and insulation that we can and we still see a drop of temperature in most rooms of about 0.4C per hour. before it stabilises at about 13-14 C. Having never been interested in measuring internal temperatures or losses whilst we had a gas boiler I now find myself wondering whether this is a good, bad or indifferent rate of temperature decrease for a year 2000 build 4-bed house? Any views on this?

All opinions and pointers welcome as I don't want to spend if I don't need to, and all it might need is a system tweak somewhere that I am unaware of.

Cheers

Al



   
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cosy home Heat Loss
 davidnolan22
(@davidnolan22)
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Joined: 11 months ago
Posts: 135
26/11/2025 6:57 pm  

13 degrees! is that a typo? who installed that?



   
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 JamesPa
(@jamespa)
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Joined: 3 years ago
Posts: 3712
27/11/2025 8:50 am  

Posted by: @alastair
↑

All opinions and pointers welcome as I don't want to spend if I don't need to, and all it might need is a system tweak somewhere that I am unaware of.

Cheers

 

0.5 C per hour is quite fast.  

14kW is enormous, how big (floor area) and what construction is your house

Increasing emitter size is almost always good.

Before you spend any money, how is your heat pump controlled, is it on 24x7, have you balanced the emitters, are you using trvs?


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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 alastair
(@alastair)
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Joined: 4 years ago
Posts: 36
Topic starter 27/11/2025 10:22 am  

Hi.

We have a 112 m2 year-2000 built standard box.  We were originally told that we'd have an 11kW heat pump but on the day of installation we found out it was a 14 kW unit. We were told that it would be fine - maybe we should have questioned this more but the installer said it would make the heating easier. Our heat pump is controlled using a Salus thermostat for turning the heat pump on and off, and each radiator is controlled using TRVs. 

To be clear, the drop in temperature at the rate I mentioned is when the heat pump is off, and the outside temperature is 8C or less. We have draught proofed everything we can think of, have new windows and doors, have cavity wall insulation and double the recommended depth of roof insulation. We just cannot think why the rate of heat loss is so quick.... We have air bricks so the only thing we can think of is that the heat is lost through the floor somewhere, but a thermal camera survey doesn't show anything obvious. Thank you for confirming that a rate of 0.5C/hr is at the higher end - we also thought it was a bit high! 



   
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 JamesPa
(@jamespa)
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Joined: 3 years ago
Posts: 3712
27/11/2025 1:22 pm  

Posted by: @alastair
↑

Thank you for confirming that a rate of 0.5C/hr is at the higher end - we also thought it was a bit high! 

Its nothing to do with the heat pump of course, something about the house.  It could just be that its very low heat capacity (which can happen if all the brickwork etc is external to the insulation) so even with a low loss cools quickly.

 

Posted by: @alastair
↑

We have a 112 m2 year-2000 built standard box.  We were originally told that we'd have an 11kW heat pump but on the day of installation we found out it was a 14 kW unit.

11/14 doesnt matter if its Daikin, all the 9+ ones are identical hardware, all of the 8- ones are identical hardware, they just software limit the output.

However with that house you should only need a 5kW heat pump!  

Posted by: @alastair
↑

Our heat pump is controlled using a Salus thermostat for turning the heat pump on and off, and each radiator is controlled using TRVs.

Thats about the worst way possible to run a heat pump (they should generally be run 24x7 without TRVs or thermostats on a weather compensation curve) however if you are happy with the cost and comfort not to worry

 

Do you know how much energy you use (or better still how much the heat pump reports it delivers to the house) in a year, or on any given day of the year?

Apart from the high rate of temp drop is there anything concerning you?

 

 


This post was modified 3 weeks ago 2 times 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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 AndrewJ
(@andrewj)
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Joined: 11 months ago
Posts: 133
27/11/2025 5:27 pm  

Posted by: @jamespa
↑

they should generally be run 24x7 without TRVs or thermostats or a weather compensation curve

@jamespa did you mean ... ON a weather compensation curve rather than OR?



   
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 JamesPa
(@jamespa)
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Joined: 3 years ago
Posts: 3712
27/11/2025 5:45 pm  

Posted by: @andrewj
↑

Posted by: @jamespa
↑

they should generally be run 24x7 without TRVs or thermostats or a weather compensation curve

@jamespa did you mean ... ON a weather compensation curve rather than OR?

Yes, sorry.

 


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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