On HeatpumpMonitor, you can compare data from two or more systems.
You can also compare a system to itself, across different dates by unticking the “Match dates”.
This could be useful to assess the impact improvements that have been made.
For example, I’ve compared my system (#1) over the last 3 months (red) against the same period in the previous year (blue), having switched out the room thermostat I was using:
To my eye, the system appears to be running better this winter. 
PS: There’s a bug with the date controls that don’t like 2024.
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I’ve just wanted to do exactly this, compare my own system to itself over the last two weeks but I think the bug you mentioned you 2024 dates is making this not work.
It would be great if this could be fixed as it makes assessing the performance impact of any system settings changes straightforward.
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Being a bit cheeky and tagging @TrystanLea as I know you dev the site and just wanting to flag this apparent bug on the comparison page.
I have fixed the bug. Might need Trystan to nudge the server to accept the change.
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This fix is now live at https://heatpumpmonitor.org/compare so you can now compare (say) this winter to last winter.
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Thanks for sharing this, it’s a very useful tool to try and figure out if small tweaks to the system are improving things or making this worse!
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Yay for the fix! The bug was preventing me comparing my Daikin 9kW before and after the tape heater fix.
Blue is before the fix, green is after 
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