`Considerations ==  Terminology: There is growing preference to use 'poured' vs 'wet' since a wet floor can be interpreted as a negative feature. There is growing preference to use 'sub floor' vs 'dry' since a dry floor can be interpreted as a negative feature.  System Hydraulics: This paragraph needs a rewrite: ``Because it offers a good balance between cost and pressure drop, ⅝-inch diameter tubing is popular: ¾-inch and 1-inch tubing are relatively expensive, and ⅜-inch and ½-inch offer too much resistance, which means more energy consumption to pump the liquid through the pipe; and the ⅝-inch tubing is often the minimum size needed for effective thermosiphon.``  Reason: Pipe dia. selection should first be selected on velocity; a function of flow based on design delta t and fluid/pipe characteristics. There can be equal or less energy consumption in 1/2`` or 3/8`` if the loops are shorter and velocity is lower by using larger delta t's so long as the velocity is kept above a nominal 1.5 fps. Often times inexperienced designers use larger diameter pipe without considering the effects on heat transfer or air and solids separation. Also it is very difficult to install larger diameter PEX in cold climates and in some ``sub floor`` systems.  More often than not 3/8 and ½” are more than adequate for most projects. Where long loops are required, 5/8” to 1” should be considered but again ensuring that velocities  do not drop below a nominal 1.5 fps.  Energy Savings: This needs to be clarified. ``Energy savings of up to 40% can be achieved compared to conventional heating systems if a condensing boiler is installed, but even with a standard boiler up to 15% energy savings are normal``  Reason: See IEA LowExergy site re: ``energy savings vs exergy savings``. There are research projects which suggest there is no measurable savings when comparing a hot air furnaces or hot water boilers of comparable combustion efficiencies. See PATH Partnership Research on Habitat for Humanity Houses. See also NRCan/IRC Research Project comparing radiant to hot air.  Also, the more efficient the home the less importance in mechanical efficiency. I.e. in a net zero energy home there is no payback for high efficiency equipment or we can say the most efficient system is the one which never runs.   There can be reduced use of energy with radiant but the ``how`` must be specified.   Other comments to follow.    == `