DREG Posted February 19 Posted February 19 If you have a heat loss/load calc that says 10.3 kW, what output heat pump would be recommended (new build house, EPC B) The MCS MIH documents don’t state clearly how many kW you need to allow for DHW and defrosting. Appreciate you do not want to oversize it; but equally is there a danger of under specifying it?
JohnMo Posted February 19 Posted February 19 (edited) New build and 10.3kW sounds huge. Have you checked the heat loss calculation. Post it on here to be reviewed. Or go into boffins corner and find the heat loss calculation spreadsheet and do your own calculations. To put some perspective on the number 10kW x 24hrs is 240kWh a day. A CoP of 3 is 80kWh of electric per day. Or £20 per day, just for heating. Edited February 19 by JohnMo
JohnMo Posted February 19 Posted February 19 Also my build, around 200m², very poor form factor, vaulted ceiling in every room. If it was built to minimum building standards and didn't have responsible airtightness and MVHR would be about 5-6kW at -9.
Conor Posted February 19 Posted February 19 we went for a heat pump with 90% more capacity than heatloss as we run it over 7hours on low rate rather than 24hrs. You'll be looking at a 12kW pump or bigger regardless of how you run it. A key thing is how low the heatpump can modulate down to. Ours ranges from 2.5-9kW, our heatloss is ~5.5kW and we run the system as two zones, so there's never a risk of being over powered. You do NOT want to be under-powered.
ReedRichards Posted February 19 Posted February 19 (edited) My calculated heat loss was 8.94 kW and I have a 12 kW heat pump. I live in a timber-framed bungalow built in 1980. The most the my heat pump has ever used in a day that I recorded is just under 60 kWh. By @JohnMo's figures that would have cost me £15 for that day. However my average usage is about 16 kWh per day for both heating and hot water. Something that you need to understand about heat pumps is that it's the seasonal average that hits you in the pocket; you shouldn't get hung-up on worst case scenarios and costs. Edited February 19 by ReedRichards
DREG Posted February 19 Author Posted February 19 3 hours ago, JohnMo said: New build and 10.3kW sounds huge. Have you checked the heat loss calculation. Post it on here to be reviewed. Or go into boffins corner and find the heat loss calculation spreadsheet and do your own calculations. To put some perspective on the number 10kW x 24hrs is 240kWh a day. A CoP of 3 is 80kWh of electric per day. Or £20 per day, just for heating. I’m doing this retrospectively as house was built in 2021. I’ve been trying to get hold of the data but it’s like pulling teeth. I believe this is the heat calc that was used by the heat pump supplier/installer
DREG Posted February 19 Author Posted February 19 (edited) There have been other heat calcs done….. heat loss 29-1-25.pdf Edited February 19 by DREG Incorrect file
JohnMo Posted February 19 Posted February 19 Compare the U values used to your build. Was an air test completed? Do you just have intermittent fans in wet rooms for ventilation?
DREG Posted February 19 Author Posted February 19 4 minutes ago, JohnMo said: Compare the U values used to your build. Was an air test completed? Do you just have intermittent fans in wet rooms for ventilation? Asked for air test result but none found. Was sent the SAP report. The bathroom and en-suites have switchable fans with isolator.
DREG Posted February 19 Author Posted February 19 1 hour ago, DREG said: I’m doing this retrospectively as house was built in 2021. I’ve been trying to get hold of the data but it’s like pulling teeth. I believe this is the heat calc that was used by the heat pump supplier/installer I think the specified room temps are incorrect: they should be 21C, according to NHBC TECHNICAL GUIDANCE 8.2/01. External temp should be -3.3C.
nod Posted February 19 Posted February 19 6 hours ago, JohnMo said: New build and 10.3kW sounds huge. Have you checked the heat loss calculation. Post it on here to be reviewed. Or go into boffins corner and find the heat loss calculation spreadsheet and do your own calculations. To put some perspective on the number 10kW x 24hrs is 240kWh a day. A CoP of 3 is 80kWh of electric per day. Or £20 per day, just for heating. So very true We have 400 m2 over two floors with three vaulted ceilings and 2.7 ceilings for the rest So Bang It has to be 11kw All threes software said so One told us we would need two HPs I think they have to go with worst case scenario We would have been fine with a smaller HP We are using between £9-13 per day at the moment for heating and two baths per day
DREG Posted February 24 Author Posted February 24 On 19/02/2025 at 17:43, JohnMo said: Compare the U values used to your build. Was an air test completed? Do you just have intermittent fans in wet rooms for ventilation? Air permeability from SAP report
sharpener Posted March 2 Posted March 2 (edited) On 19/02/2025 at 12:40, DREG said: If you have a heat loss/load calc that says 10.3 kW, what output heat pump would be recommended (new build house, EPC B) The MCS MIH documents don’t state clearly how many kW you need to allow for DHW and defrosting. Appreciate you do not want to oversize it; but equally is there a danger of under specifying it? Vaillant 12kW would do nicely IMO. Specd down to - 20 so at -3C the data sheet figures give quite a bit in reserve for DHW and defrosting. Quite good turn down ratio so cycling not too much of a problem. Very quiet. The 10kW is the same hardware de-rated so no point in choosing that, min o/p is the same. Mitsi also a sound choice if that is what you have been quoted. Edited March 2 by sharpener
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now