Whidbey - the use of nails for flooring is not forbidden; it depends upon the type of installation used for radiant heat. In fact, there is very big business in retro-fitting for radiant, under hardwood floors (which have been nailed). mdev ~ before any glue is used, discuss with its manufacturer to be sure it is suitable for radiant heat installations. Most adhesives are okay, but some radiant systems use *very* hot water, which can cause some adhesives to become brittle or otherwise lose gripping effectiveness. I would also question the potential for out-gassing from glues, although don't be surprised if you get a generical response of 'that's not a problem' instead of test results.

I put radiant heat under my wood floors and it works very well. The floor is just pine over wood joists and plywwod subfloor, and not engineered.. I did pay close attention to insulation, isolation, heating loops, tube spacing, loss calculations, all that good stuff. I get some seasonal gapping in the wood though frankly it's hard to notice, and it's not any different than what I got without radiant heat. The one thing I did regarding controls was to use both a floor sensor and a thermostat for each zone. The thermostat runs the system but if the floor heats up to a set temperature (I use 85 deg F) the system shuts off - that way the floor never gets hot enough to damage the wood, if it could damage the wood, which I'm not sure of. I've heard good things about the control system that funnycide mentions (water temp function of outside temp) but I get pretty good performance with my water at a constant temp - very comfortable and fuel efficient.

We have 2800 square feet of LVT throughout the first floor of our ranch house, bathrooms and kitchen included, and it is gorgeous. They were professionally installed; the subfloor was leveled so that there are no door transitions or height differences throughout, and it is a stunning look. Downstairs basement is engineered hardwood. If we ever need to redo the floors in the basement, it will be LVT. There is no going back; it is just too lovely and practical. The cork backing of the LVT makes the floors very comfortable underfoot, and they are very quiet. I considered tile with radiant heat until I spent a week in a beach condo with tile floors; they felt too hard under my feet.

Is there any way to measure the temperature at the 'wood-subfloor' interface? Most floor products do NOT allow anything warmer than 85F at the subfloor-floor interface (the temperature found between the two products). The 60 F INSIDE temperature is quite low. It is just on the very edge of "indoor living temperature". Most warranties (paint, carpet, hardwood, baseboards, doors, drywall, cabinets, etc) must have consistent indoor living conditions. The building industry has a definition of indoor living conditions (which are to be maintained throughout the life of the home...regardless if someone is home or not). Relative Humidity: 35% - 65% Temperature: 55F - 85F Your indoor air temperature is only 15 Celsius. That is VERY cool. The lower temperatures have a harder time 'keeping' moisture in the air. That's why you find dew on the grass during the chill of a spring morning. The grass is colder than the air. And the air is already quite chilly. The air has a hard time 'holding on' to the water vapour. The cooler blade of grass is JUST ENOUGH to cause a water droplet to form - pulling the water from the air and onto the earth. As the air warms up, the vapour is HAPPILY stuck in the air. That's why you have hot-sultry areas (like NYC in the summer time) and you have cold DRY areas (like Mongolia in winter). It's how the laws of physics work. I would tip up the heating a snick and OPEN THE WINDOWS to pump up the humidity. I would bet the closer you get to 50% RH and 70 F (20 C) the better your floors will look. Somehow you need to get the humidity and the temperature up AT THE SAME TIME.