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There is a simple system diagram on page 9 here https://www.underfloorheatingsystems.co.uk/wp-content/uploads/2016/04/UHSSINGLEROOMPACKINSTRUCTIONS.pdf
I have never tried wet underfloor heating, I did try a small electric system that failed a few weeks after the tiles had been laid on top - so I put in another radiator.
I assume that the system boiler has its own internal pump so you just need another pump for the underfloor and mixing valve set up, it may come as a combined unit. A pump with good low flow efficiency, as above, seems a good idea.
A 40 kW boiler seems way over the top for this system, it will heat up very fast and then have to turn itself off and on every few minutes, except in extremely cold weather. The underfloor system has a max demand of 2.1kW or 1.5kW under a wood floor. There will be long periods when the underfloor system is the only demand so the low end performance of the boiler is more important than max power available. If the building is well insulated and double glazed in an urban area then 24kW would do, on an exposed site or with dodgy insulation you might want a bit more power.
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Charlie_L
We're in the process of having an extension built, which is getting underfloor heating within it. As part of the work, we've got the chance to separate the heating into 3 zones, upstairs Rads, downstairs Rads, and the underfloor area. We also have a hot water cylinder.
I've drawn a simplified diagram of what I think the layout will end up like here - https://pastebin.com/DNMzvuic
I'm fairly happy that I've got the boiler picked as an Intergas Compact HRE 40 SB.
Valves will be Honeywell V4043s.
And a Nest Thermostat to control each zone.
I've been looking at pumps to try and work out what would be needed there. I currently have a Grundfos UPS2 15-50/60 but don't know if this would be suitable for the new setup. Could someone advise on this? if not, which of the Grundfos pumps should I be looking at?