[wernerb]

This needs far more attention. Combi boiler installers tend to massively oversize the CV. But with heat-pumps you need to be far more accurate. And it does not make sense to design for a temperature that occurs only a couple of days in the year. You can just have the backup heater kick in which is far more efficient for a couple of days than having a heavier heatpump for the rest of the year that can not modulate back as much as a smaller heatpump.

[stilley2]

I recommend this technology connections video which dives into this in wonderful detail https://youtu.be/DTsQjiPlksA?si=gx18FGOcjsv5PpNg

[rssoconnor]

> than having a heavier heatpump for the rest of the year that can not modulate back as much as a smaller heatpump.

Aren't basically all modern heatpump variable speed, and thus can modulate back?

That said, I totally agree with your overall point about right-sizing your heat pump, but it is more about saving money on the unit rather than worrying about cycle times.

[bluGill]

Modern heatpumps can modulate, though it isn't 100%. I recommend people consider two smaller heat pumps in many cases - it costs more upfront but can modulate down more and if one system breaks the other can handle everything most days of the year (some rooms will be a bit uncomfortable)