Underfloor central heating - unusual system

4 Nov 2011
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West Midlands
United Kingdom
Hi all,

Firstly very grateful for any advice received.

In my house I have inherited a hybrid underfloor/radiator - oil fired central heating system. The previous owner was an 'irrigation engineer' and very much liked concrete. He lifted all the floors and installed a wet piped heating system - covered with a sort of fibre infill and then with around 5 inches of concrete as far as I can tell. This is all connected to a bespoke manifold with taps to all the underfloor sections - controlled by gate valves - I have a cupboard that could pass as part of a ships boiler room. Upstairs there are 4 radiators for heating - giving about 6 Kw at a guess. Hot water is taken care off via a conventional hot water tank - gravity system. The system is open vented with a loft tank for expansion. The underfloor heating works OK - the boiler runs and the pump circulates the water and the UFH slowly warms up the floor - boiler switches off and the UFH slowly cools down - never feel 'roasted' but never feel cold. The problem is that the UFH is fed from the manifold with what looks like 22mm pipes - 8 in total, whereas the upstairs rads are fed from a 15mm spur - not a great deal of heat gets upstairs - and takes a long time getting there. Because the water gets slowly warm for the UFH - larger volume with slower heat dissipation the radiators upstairs only heat up slowly - like really slowly. I suspect that the flow rate is insufficient - even with the rads at minimum resistance to flow. Suspect that 1x15mm v 8x22mm does not help.

My question is - what would be the best way to increase the volume of heat reaching the upstairs radiators (they are on a conventional parallel circuit spurred from the underfloor system manifold). I am a bit reluctant to throttle down the UFH on the manifold to try and increase the radiator flow - visions of installing a new set of 8 gate valves (hate them) or unnecessarily pressuring the system at that point. Would it be feasible to place a small pump on the 15mm section for upstairs to increase the flow. I could then cannibalise some of the hottest water from the output manifold for upstairs. What would be the best way to regulate this type of arrangement - I would not want the secondary pump to pull all the hot water away from the UFH.

Many thanks for your help.
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You need to step back and look at it from the other direction!

Lowering the flow to the UFH.

The UFH should also be controlled and timed seperately to the radiators!


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