[buffalobillpatrick]

MMT,

I feel that insulation is cheep $ that saves $$$ heating bills over time.

No heat transfer plates.
Don't want noise, expense of plates & instilation time.

Cast Iron boilers love to run hot, most need the return water above 140*F to prevent condensation which leads to rust & and an early grave, Son's Burnham ESC6 it's 120*F

Heat transfer Plates are not needed with high water temps. & suspended 1/2" pex 4" OC.

There is a convective plenum under the subfloor of about 4" with the pex in the middle, R30 below.

This is now a method recommended by Uponor (Wirsbo) largerst pex producer in world.

I was actually offered an engineering job interview (free flight meals & lodging trip) with them in Minneapolis St Paul 10 yrs ago, after I retired from IBM. I asked if I would have to live there in winter, manager said yes so I said no thanks.

In my Son's house @ -20*F outside, the hot water going through the pex is 165*F on average, the convective plenum air reaches about 145*F on average,

With a 30:1.5 ratio, about 95% of the heat fights it's way up through the R1.5 (3/4" subfloor + 3/4" hardwood flooring),

With a room AUST (room average unheated surface temperature) = 70*F
the hardwood surface reaches 87-88*F,

& releases 35btu/ft2/hr through radiation + convection.

I actually tried to talk my Son into doing it like we did my neighbors house.
It has 2x4 sleepers on 12" centers above subfloor with 1.5" x 8.5" of concrete (no rocks) around each 1/2" pex run, Hickory flooring nailed to sleepers.

We could have run cooler water temps. with more margin for extra heat if it gets down to -30*F outside

He said NO, as my house works so well.