Connection point of new UFH to existing radiator system: manifold near boiler

27 Feb 2005
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United Kingdom

I currently just have radiators for heating with an S Plan Plus setup (separate zone valves for downstairs and upstairs, plus valve for hot water cylinder, plus summer circuit for towel rads receiving heat whenever one of the other three call for heat). Boiler is a Potterton Promax SL (very basic developer spec condensing boiler, but works fine at present).

I would like to have wet UFH in a proposed extension. I know the normal schematic would have the UFH run from an additional zone valve after the pump, that would lead on to the blending valve, UFH pump and manifold, with return back to the boiler.

In my property, that would be technically possible, noting that the airing cupboard is about 10m pipe length away from the boiler on the other side of the house. The boiler flow runs to the airing cupboard, which houses the pump, existing three zone valves, and the returns are combined for the 10m run back to the boiler.

However, the ideal manifold location for the new UFH is almost right underneath the boiler. Therefore, what would be the best way of getting boiler output to the UFH?

Option 1: The aforementioned flow and return to the airing cupboard is doable. I would certainly want the pipes lagged (I plan to get the existing boiler primary done anyway, disappointing for a relative new build that it was not) to avoid overheating the rooms above. Some of the ceilings would be down, while other carpets could be lifted to make the route possible. Though this option means the water goes from boiler to airing cupboard, back to under boiler for the manifold, then return back to airing cupboard then to boiler. So about a 40m run.

Option 2: Need the UFH return go back the airing cupboard, or could it join the existing return near the boiler, eliminating half the journey above?

Option 3: Alternatively, is there a shortcut method of both flow and return going straight from the boiler? The existing pump is not going to push the water down that circuit, while the UFH pump might be insufficient to get enough flow through the boiler, so I could foresee it needing another pump. Could such a loop, perhaps only 3m at most round trip from boiler to blending valve and back, be too short?

Though the reason I am thinking about this is that maintaining a 40m or 20m (from options 1 and 2) loop of 70 degree water circulating when only UFH is calling for heat seems wasteful when that UFH needs blending down to something cooler anyway. Though it is in the context of about 55 square metres total floor space being heated.

While I would not be planning to do the UFH fitting myself, and will inform of the boiler and airing cupboard location when getting quotes, I would like to understand whether what gets proposed is a good way of doing things and not unnecessarily wasteful, and not too much of a bodge either. In avoiding waste, I am thinking of efficient operation, not just saving on pipe at outset.

I am aware of buffer tanks and thermal stores but they would seem overkill for this application. I am also aware that some have UFH as part of the radiator circuit: this is something I definitely do not want so that I can have independent control of the UFH given the slower warm up.

Any thoughts welcome.

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