Renewable Heating Hub Heat Pump Forums

Search with Wattson
Forums
Renewable Heating
Air Source Heat Pum...
Heat loss based on ...
 
Notifications
Clear all

Joining the Renewable Heating Hub forums is completely free and only takes a minute. By registering you’ll be able to ask questions, join discussions, follow topics you’re interested in, bookmark useful threads and receive notifications when someone replies. Non-registered members also do not have access to our AI features. When choosing your username, please note that it cannot be changed later, so we recommend avoiding brand or product names. Before registering, please take a moment to read the Forum Rules & Terms of Use so we can keep the community helpful, respectful and informative for everyone. Thanks for joining!

Heat loss based on gas usage

 
Air Source Heat Pumps (ASHPs)
Last Post by Bash 9 months ago
3 Posts
2 Users
0 Reactions
1,074 Views
RSS
 Bash
(@bash)
Reputable Member Member
Joined: 1 year ago
Posts: 228
Topic starter 11/01/2026 9:26 pm   [#2732]

We are 2 weeks away from our HP install.

In October I dropped the flow rate down on our Vaillant gas boiler to 45c, to match our HP design temperature.

We are upgrading all the radiators as some are way to small and others need increasing to meet the design temp of 45c.

I set the thermostat to 21c with a setback to 19.5c between 9pm and 5am.

Surprisingly this has significantly improved the comfort of the house, without increasing gas usage.

We have a warmer house.

I upped the flow to 50c during the cold snap of the last few weeks.

The house has stayed warm 24/7, which bodes well for the HP.

The gas boiler has run nearly 24/7 over this period.

Our heat loss was calculated at 6.2kw @ -2 45c.

Below is our gas usage for the coldest day Tuesday 6th Jan, which ranged between -8c and +4c

This looks like our heat loss calculation was bang on (to me).

Have I interpreted the gas usage right from the bright app?

Thanks.

Screenshot 20260111 201524

 

Screenshot 20260111 203025

 


This topic was modified 9 months ago 3 times by Bash

   
Quote
JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 4 years ago
Posts: 5520
11/01/2026 9:59 pm  

Posted by: @bash
↑

Have I interpreted the gas usage right from the bright app?

In a word yes.

 

Measurements  based on a single day should be treated with extreme caution, houses take a long time to react.  However as a general indication this is likely to be good.

 

Like you I turned down my gas boiler before getting a heat pump and like you it improved comfort.  Unfortunately the way boilers are typically run in the UK increases cost by about 10% and reduces comfort.  Madness!


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.


   
ReplyQuote
 Bash
(@bash)
Reputable Member Member
Joined: 1 year ago
Posts: 228
Topic starter 11/01/2026 10:12 pm  

@jamespa 

Thanks.

The numbers posted above were just for the coldest day over the last few weeks.

Looking through the bright app it's similar across many days over the last few weeks suggesting it's not a one off.

Last winter we had our flow temperature at 65c and set the thermostat to 19.5c during the day and 17c overnight.

This resulted in the heating coming on for about 1.5-2hrs and switch off for 2-3 hours.

The house was significantly colder and less comfortable.

Comparing gas usage we don't appear to be consuming any more so far than last winter (which wasn't particularly cold).



   
ReplyQuote
Forum Jump:
  Previous Topic
Next Topic  
Share:

SPONSORS

Join Us!

Installer Finder

Degrees of Separation

Latest Posts

SPONSORS

Click to access the login or register cheese
Protected By
Shield Security PRO