<html> <head> <meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> </head> <body text="#000000" bgcolor="#FFFFFF"> Will, Jim, Jon, Ron etc, thank you for these responses. They are really helping me to think about what goes on in a room with infloor radiant heating.  Jon, I think I have to agree with the comments which point out the DISsimilarity with radiators.  The surface area is much larger and the surface temperature much lower. The question of RH is surely pertinent.  It is therefore worth mentioning again that the house is located on the west coast of Scotland which has a mild and VERY rainy climate. In addition it is right by the side of a large loch (see pic from front door).  It is, in short, in as damp a geographical situation as can be found in Britain.  Short of having permanently switched on, a powerful electric dehumidifier of the compressor type, the air in the home is NEVER going to be excessively dry, whatever its temperature. I don't therefore see low RH as a potential problem. That just leaves temperature itself.  How many degrees higher is the air temperature on or just above the surface of the floorboards, than, say at piano key height in the room?  I do not know.  Surely not as much as, say, 20 degrees Farenheit?  SUch that, if the air in the room were at a comfortable 70 degres F, the floor would be at 90 degrees F?  Even if the wooden floorboards WERE at 90F, given that the air does not have low RH, how would temperature at the bottom of the piano damage it?  By melting hide glue?  I take your point tho, Ron, about the moisture content of the wood in the piano potentially changing with the seasons as the underfloor heating goes off. I am going to put these thoughts to the owner, who is an engineer, and see what he makes of it all! Ron, I enjoyed the "leak to inherit the earth" remark, and the anecdote!  Lots of builldings, including apartment blocks and tower blocks, were built here in the 1960s to designs that were simply unsuited to the climate.  Almost all the flat roofs, including those on 18-storey tower blocks, had pitched roofs put on them eventually. Best regards, David.   </body> </html>