I know that Shaun.
We don't know the circuits though do we and even modulating pumps have a minimum performance. If he is guessing, it is better to try and avoid over-sizing as well as under-sizing something. Very difficult. I like to 'know' what the outcome will be rather than guess. If you have a very small circuit on a pump which is over sized, you will have issues.
This isn't the way I would do it and I was only trying to offer some advice based on the small amount of information I have.
Whilst on the subject of pipe sizes, the figures you posted elsewhere but to the same OP as a rough guide, seem high to me. Where are they from?
15mm 20kw
22mm 40kw
28mm 70kw
Thanks for your info. Like I said there’s 21 plus rads inc unvented cylinder and some very long runs of pipes in 22. Some of the 22 legs running 16 plus metres flow with 4 rads each about 1.5 - 2kw rads.
I’m fitting the IMI trvs with inbuilt flow setting. So I size the rad off their app and set the trv internal setting to a number which corresponds to the required flow rate of that rad. I’m hoping this helps settle things. I’ve tried as much as possible to size everything.
like the drawing shows I’ve got 2 boilers 18-25kw
Both 22mm cascading into 28mm. Running about 6m to a LLH (sized correctly) then to the pump(not known which yet) then to 42mm header with 3 zones.
so is the consensus to use separate 15/60 on the zones or one main pump after LLH?
the below image shows day one. Note the distribution header is positioned on this photo is to be sited to the right of where it is now. The pump will fit in this gap.
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If it were me, I would do two designs one for the best and one for worst cases of the pipework I cannot easily access. Oversize the header and then look at other areas where oversizing would give you more flexibility.
I don’t like noise from a heating system so I am always looking to keep the velocity At the low end of the specification.
With respect to pump, if you follow the above, at least the required range will be evident.
Sometimes, if you are really unsure, the multi pump option can give you more flexibility to fine tune an existing system that has not been properly designed.
As always, you can throw together a ten rad system and get away with it - but that is far less likely on a 20+ rad system.
Hope this helps
So looking at my recent reply would you go separate smaller pumps as apposed to one big? I know it’s difficult to guide me without seeing it but I’m thinking both will work.
Downside of the large pump I’m thinking if there’s only one small zone open, it could be noisy unless the pump can modulate right down.
Separates would require 3-4 pumps and valves which obviously more expensive.
The current house is running off one circuit , one 15/60 and doesn’t work very well (obviously)
