A turndown ratio of 2:1 is commonplace, 3:1 unusual but some Vaillants achieve itGarethC wrote: ↑Fri Jun 28, 2024 10:46 pm I thought inverter based heat pumps modulated effectively, so didn't realise oversize one would cycle inefficiently. In fact, I was under the impression that oversizing could be beneficial, as HPs running at partial loads achieved higher COPs.
Not sure where I got that from though...
So the modulation of even the best HPs is nowhere near as good as a modern boiler. Partial load improves CoP per se by about 0.5 at best, but of course if you want less output you can also run you emitters (rads/UFH) at a lower flow temp which makes a bigger improvement.