I have recently carried out a design with an open plan area, that was 140m2 and wherever I placed the Manifold, I was always exceeding the maximum of 12 circuits. When I tried to add a second manifold and partition loops, and then allocate circuits equally over the 2 manifolds it wouldn't work and only one Manifold would generate loops. Having the ability of having multiple manifolds in one area, should be a standard option with UFH designs.