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Air Source Heat Pumps (ASHPs)
Last Post by Redguy17 9 months ago
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 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 3249
06/02/2025 12:29 pm  

Posted by: @redguy17
↑

my annual gas ussage is 26786 KwH( heating and hot water)

bolier is over 15 years old ( estimates 87% efficent)

i work at home so heat is on all day every day usually to 19 degrees

20% of the house ( a bed room and ensuite) are currently heated with electricity.

Currently during October to February we use about 6 tonnes of wood as wood burner is on from 6 am till 6pm most days.

Wow, thats a lot of gas - you said 120 sq m is that the total floor area or just the ground floor footprint?  For comparison my 200sq m detached was about 20kWh gas consumption/7kW loss.

6 tonnes of wood adds about another 24MWh making 50MWh consumed in total on heating plus hot water, even without the electric.  If we assume 85% efficiency thats still 43MWh, which equates to somewhere between 14 and 20kW loss.  Do you have a lot of long showers or keep the windows open a lot?  

 

Posted by: @redguy17
↑

PS. my pipe work is already 28mm . heat loss was calculated as 9.8 and 10.9 respectively. a Vaillant aro therm plus

10/12 kw double fan unit has been suggested by both.

If the consumption figures are correct then 9.8/10.9 appears to be an underestimate for the loss. However lets run with it for now.

The Vaillant double fan is a bit of a monster size wise, but there are several single fan models doing up to 12kW.  Mitsubishi for example do 11.2 in rather neat single fan format.  Others do single fan also but sometimes wider.  it might be worth contacting someone who does one or two of these?

I would be very concerned about your consumption though, unless there is an explanation buried in my questions above.  It seems just too high which makes me wonder where the heat is going!  Perhaps you can shed some more light by answering the questions above?


This post was modified 9 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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 Redguy17
(@redguy17)
Active Member Member
Joined: 9 months ago
Posts: 7
Topic starter 07/02/2025 11:49 am  

@james PA 

My kids do like a bath and have two a day wife also has two showers a day so possible our hot wter usage is bumping up figures alot.

 

Just got this back from local guy.

Revised heat loss down to 8

Changinf 5 rads up to double units ( 1600 x 600)

 

and this heat pump

Mitsubishi R32 heat pump WM85 (MCS accredited) with a thermal output of
8.5kW at an outside air temperature of -7oC
temperature of -15oC and a maximum flow temperature of 75oC
• Mitsubishi flow temperature controller
• 200 litre unvented domestic hot water heat pump cylinder
 
this seems alot more reasonable than his inital estimates. he is granteeing a scop of 3.47.
 
seems like heat pump is back in the cards for me now!
 


   
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