The easiest advice, but perhaps not the most helpful at this juncture, would be simply to advise you to use a professional floor installer with plenty of experience laying hardwood flooring over underfloor heating systems. We have literally thousands of meters of hardwood floors laid over underfloor heating systems; fitted and commissioned correctly we have not experienced any problems.
Must underfloor heating systems involve laying pipes over or within insulation on the ground floor slab. The pipes are then buried in a screed which heats up to provide constant low level warmth into the room. As wood is an insulator, the passage of heat from the pipes through the floor and into the room is affected by a ‘lag’. This tends to result in the pipes having to heat up more so that the boiler works for longer before the room thermostat kicks in and switches it off. Conversely, there is then a period of overheating from latent heat stored in the wood and pipes.
That said, underfloor heating is becoming very popular and as a method of heating is definitely here to stay. This move from traditional radiated heating systems can generally explain the demand we have seen in the market for engineered wood floors in recent years. This is a type of construction which is made of of a layer of real wood (the surface top layer) with a sandwich layer several cross-layers of plywood or softwood bonded to the back. Essentially it gives the appearance of solid wood but with far more stability when introduced to an environment, such as a home, where the changes in humidity and moisture can be very great. Solid wood, especially the wider boards, will naturally ‘cup’ or ‘twist’ given any opportunity. The cross-layering of wood material used in an engineered board disperses the stresses from the top layer and literally will hold the wood in shape when exposed to excessive moisture or humidity ingress or egress.
You should be wary of acclimatising the wood during the commissioning phase of the underfloor heating As both the wood and the ‘wet’ screed are in the same room, the moisture forced out of the screed during commissioning is taken into the wood from the surrounding air. When the wood is laid without checking the moisture content, it releases the excess moisture and shrinks. Gaps appear and the room is spoilt. There is less chance of this happening using engineered wood, but the problem can never be completely eliminated.
Care, attention and the right experience as well as your supplier hopefully wanting their product to live up to your expectations will ensure a successful outcome.