CH Pump Sizing

[baggy99]

I am renewing a duff boiler and thought I may as well change the old pump while I'm at it. Thing is, I've realised the existing pump is potentially undersized for the number of rads. Its a 5 bed house with 23 rads. They are all on TRVs but generally 5 or 6 are turned fully off, but even then I understand "standard" domestic pumps are only intended to drive around a dozen rads.
I don't fully understand pump ratings, eg 15/50, 15/60, 25/50, etc. Would a bigger pump help with circulation? (The old system was a bit sluggish at the far end of the lines, but I never gave it too much thought till now....)
Finally, I wouild ideally like to go for a smart pump (eg alpha) since the system is all TRVs.
Any thoughts please? Thanks.

 

[chrishutt]

Well if you're renewing the boiler with a condensing boiler you will also be operating the system with a bigger temperature drop (20° instead of 11°), so water will circulate less fast and you will not need such a powerful pump as before. A 15-60 (6 metre head)is always a safe choice, only marginally more expensive than a 15-50 (5 metre head), and can be run at lower speeds if necessary.

 

[baggy99]

Cheers Chris. Yes, the boler will be a condensing model, so it is great to know that the pump won't have to work as hard.
Would you recommend an Alpha? Are the smart pumps from Wilo (and others?) just as good, or should I stick to a genuine Alpha?
Thanks again.