Since the upper half of exterior wall surfaces usually have a higher percentage of window areas than the lower half, it is evident that thermal stratification will increase envelope heat loss. Further, increased thermal stratification means that higher average air temperatures are needed to maintain comfort at the occupant level. With this background, let's look at hydronic thermal distribution efficiency. For hydronic baseboard systems, efficiency is reduced by pipe heat conduction and pumping energy. Since pipes have much less surface area than ducts, are easier to install within insulated spaces, and usually do not leak, conduction and leakage losses can be almost negligible.
Induced infiltration is non-existent.
These same considerations also apply to hydronic radiant floor systems, though heat loss from the warmer slab degrades efficiency, and is the most significant loss factor. For heated slab floors, the heat flow is more complicated. However, radiant heating design equations can be used to estimate the extent to which heating a floor increases its losses. For raised floors, the U-value is the downward heat loss coefficient of the floor assembly. For slab floors, the U-value can be estimated by multiplying the perimeter heat loss coefficient by the building perimeter and dividing by the floor area.