How do I size a CH pump?
Posted: November 2nd, 2018, 10:46 am
I have just replaced my central heating boiler*, and sized it using Stelrad’s excellent STARS heat-loss app.
Since the radiators now seem to take longer to warm up (perhaps because the boiler temperature needs to stay within the condensing temperature window), the pump** now seems under-powered.
But how do I size a pump? It is tempting just to buy the next pump upwards in Grundfos’s range - a 180 25-80, but having done my sums for boiler sizing, I feel I should finish the job properly. And I want to avoid having a too-powerful pump that spends all its time (even on its lowest setting) over-pumping into the header tank. I am also uncertain whether to elect for conventional technology (e.g. the 180 25-80) or clever ones (e.g. Gundfos Alpha 2)
I study the various pressure and flow-rate curves for pumps servicing different heads of water, but DAK where do I go from there?
Grundfos have a sizing app which I am about to try, but what do others (e.g. CH installers) do?
Usual disclaimers - I don't work for Grundfos!
* - by a 35KW Viessmann Vitodens 100W open-vent (feeding 22 radiators and two DHW cylinders)
** - the ubiquitous Grundfos UPS2 50/60
Since the radiators now seem to take longer to warm up (perhaps because the boiler temperature needs to stay within the condensing temperature window), the pump** now seems under-powered.
But how do I size a pump? It is tempting just to buy the next pump upwards in Grundfos’s range - a 180 25-80, but having done my sums for boiler sizing, I feel I should finish the job properly. And I want to avoid having a too-powerful pump that spends all its time (even on its lowest setting) over-pumping into the header tank. I am also uncertain whether to elect for conventional technology (e.g. the 180 25-80) or clever ones (e.g. Gundfos Alpha 2)
I study the various pressure and flow-rate curves for pumps servicing different heads of water, but DAK where do I go from there?
Grundfos have a sizing app which I am about to try, but what do others (e.g. CH installers) do?
Usual disclaimers - I don't work for Grundfos!
* - by a 35KW Viessmann Vitodens 100W open-vent (feeding 22 radiators and two DHW cylinders)
** - the ubiquitous Grundfos UPS2 50/60