The good news about Edwardian and inter-war houses is the suspended timber floor. If we can get under it, we can insulate properly between the joists and run the pipe in the void — no height lost at all, no doors to ease, and a chance to fix the draughts that have been quietly costing you money since 1912. On these houses that is often the best value work in the whole project, underfloor or not.
Where the floor is solid — usually a later kitchen extension or a hall that was concreted at some point — the calculation is different. A low-profile overlay adds 15 to 20mm plus the finish, which means easing doors and thinking about the threshold into the next room. It works, but if the slab has no insulation beneath it you are warming the ground with real enthusiasm, and that needs saying before anyone commits.
Height is the constant argument in a period house. Original skirtings, original architraves and original door heights are usually the reason people bought the house, so losing 20mm of floor is not a neutral decision. We would rather map that room by room at survey than discover it at the door frame.
The pairing point matters here too, but honestly: underfloor at 35 degrees is a wonderful match for a heat pump — but only for the rooms that have it. If the ground floor is underfloor and the first floor is on original radiators, those two want different flow temperatures, and that means blending at the manifold. It is completely normal. It just has to be designed rather than hoped for.
