@jamespa 

Yes, I’m following the other thread too.

The 2900 rule of thumb is from Protons for Breakfast (and we tend to set the thermostat higher than 20C). From other posts I’ve read here it may be that with the ‘more comfortable, stable heating’ provided by an ASHP we MAY discover that we don’t need such a high temperature. 

it was only a year ago that I began investigating our heating performance and prior to that we used overnight set backs and high flow and return (non-condensing) temperatures. Before retiring the thermostat would be set back while at work during the day, too.

I completely agree regarding label ratings; that’s what I meant (but didn’t articulate adequately). 

When all is said and done, I think there are more than enough known unknowns and too many variables for me to determine the required peak power capacity with great accuracy, but I lean towards the existing performance as measured to support a discussion on, and validation of an ASHP design. 

Posted by: @ianmk13

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The 2900 rule of thumb is from Protons for Breakfast (and we tend to set the thermostat higher than 20C). From other posts I’ve read here it may be that with the ‘more comfortable, stable heating’ provided by an ASHP we MAY discover that we don’t need such a high temperature. 

Fair enough.   They must have factored in an allowance for gas boiler efficiency.

Posted by: @ianmk13

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When all is said and done, I think there are more than enough known unknowns and too many variables for me to determine the required peak power capacity with great accuracy, but I lean towards the existing performance as measured to support a discussion on, and validation of an ASHP design. 

Definitely,  which is why I favour using multiple methods.  I also plotted 3, 6, 12 and 24hr average power vs date, looked for peaks, downgraded my boiler to 8,5kW, still warm, and adjusted the ach in the spreadsheet to match the measured loss, which requires ach=0.5-0.75, plausible even though the original build is 1930s given subsequent upgrades,  known 'marginal' ventilation, and recent comments from an individual in the industry that has measured ach on several properties and has 'never measured a value greater than 1'.

Still I have sone doubts of course, but at some point design choices have to be made.  If they are wrong they won't be far out and can doubtless be mitigated on the few days in any year which are actually cold....until the gulf stream stops that is, estimated to be sometime between 2025 and 2100, with a most likely date of 2050.

Posted by: @ianmk13

↑

The 2900 rule of thumb is from Protons for Breakfast (and we tend to set the thermostat higher than 20C). From other posts I’ve read here it may be that with the ‘more comfortable, stable heating’ provided by an ASHP we MAY discover that we don’t need such a high temperature. 

Fair enough.   They must have factored in an allowance for gas boiler efficiency.

Posted by: @ianmk13

↑

When all is said and done, I think there are more than enough known unknowns and too many variables for me to determine the required peak power capacity with great accuracy, but I lean towards the existing performance as measured to support a discussion on, and validation of an ASHP design. 

Definitely,  which is why I favour using multiple methods.  I also plotted 3, 6, 12 and 24hr average power vs date, looked for peaks, downgraded my boiler to 8,5kW, (Im still warm), and adjusted the ach in 'the spreadsheet' to match the measured loss, which requires ach=0.5-0.75, plausible even though the original build is 1930s given subsequent upgrades,  known 'marginal' ventilation, and recent comments from an individual in the industry that has measured ach on several properties and has 'never measured a value greater than 1'.

Still I have sone doubts of course, but at some point design choices have to be made which, notwithstanding the claims made elsewhere, do affect many things, at least in my case, other than the odu.  If they are wrong they won't be far out and can doubtless be mitigated on the few days in any year which are actually cold....until the gulf stream stops that is, estimated to be sometime between 2025 and 2100, with a most likely date of 2050.  By 5hen this stuff is likely to be the least of my worries, if I am still alive which is doubtful.