Radiators fitted to Underfloor Heating System?

We have a couple of UFH zones that don't heat up well enough during the cold spell and I want to get a plumber to fix some rads if possible.

I want to be fully prepared for any questions he asks and to understand the requirements myself.

We have a combi boiler with it's own pump, feeding two UFH Manifolds that have their own pump each. Combi set at 75oC (max), UFH regulates it to 45oC.

I would be happy for the rads to come on even if those zones aren't calling (these room are always the coldest so I expect them to be calling for heat anyway and they will have thermostats on if I didn't want them on). I don't want to program rads on their own zone, I'm happy for them to come on when the zones call for heat and the boiler fires up.

Question is, can I get the rads plumbed on the boiler outlet before the manifolds, plastic pipe through the roof space to the rads and the return plumbed into the boiler return? Running in parallel with the manifolds if you like. Driven by the boiler pump alone, water temp to rads will be 75oC? Will it reduce flow to the manifolds?

I've not big on fluid dynamics and don't know how this will upset the system? Any advice will be appreciated.

 

Thanks for your reply.

The trouble with the room at the moment is the current UFH won't even maintain 16oC if it's zero outside even if on 24hrs, if the rads do become overpowering then I would crank them down with the thermostat vales.

I suspect either the installer ran out of pipe or the designer didn't take into account large French doors, exposed brick and 5m vaulted ceilings. Rest of the house is cosy!

So, tee-ing off the out boiler out and returning back to boiler would be ok? Driven by boiler pump?