even the load calc won't answer the ground charge issue, but if you consistently heat, that's a one time fee you pay when you heat up the system fully once a year.

Rob, re: 160K, perhaps I am misreading the old plans, then. they are quite faded. the current system can certainly output a lot of heat but floor to ceiling glass everywhere and high living room ceilings seem to require it. off to the mechanical room to vacuum some spiders and drop the boiler temp.

Judging by your boiler size, you are probably reading it right. that doesn't mean the number is right.

IF your radiant CAN maintain your room temps then your heat load is not that high though.

If it can't, even when running full tilt, well... maybe it's real then. But if so, then you certainly should be considering some other envelope improvements.

good plan,
135 is a bit hot, try 100-110, set the stat @ 68 and forget it for a couple days and see how the building feels. Rob has a point about the earth charge, with out insulation under slab you are creating a fly wheel effect you will not be able to change much with a programmable stats. Once you master the boiler temp control it will be easy to go up and down seasonally, and if you can find the way to apply the Munchkin out door reset to the boiler control that will help, don't know if at this point I would buy the expensive Tecmar set. The logic may already be in the boiler control board, I do not know though.
Tekmar does make a simpler thermostat that will work both air and slab and is programmable that wires in to any zone valve or pump control.
511 Tekmar Programmable Thermostat (kit contains thermostat 510 and slab sensor 079)
One Stage Heat. Part# 511
These work well.
Good luck,
Dan

I'm pretty sure your boiler has no reset capability without an external controller. If comfort and consistency is your goal than Tekmar 400 and the 552 rtu or 528 stats I bet you will get the over under to less than 2 degrees.

As mentioned with the large mass of dirt to heat, set back would be ineffective. At a steady heat the ground will eventually hit its steady point. How effective is indoor and outdoor resets with this mass? Do they still provide significant savings or up the comfort level? I know it changes the budget but with this much mass what do you guys think of keep the whole house at a lower temp. (say sleeping temps) and adding a fan coil to heat the air in the living areas (quick response)?? The fan coil could also integrate fresh air if the house is not already so supplied.

reset is more important with mass set to a consistent level.. makes swings less likely. If you NEED quick response then adding a low mass emitter makes sense.

Insulating shades would make a big difference in a short time: http://www.windowquilt.com/products/full_broch.htm

These would get you to R4.6, and stop overheating as well as long as someone is around to lower them. Or put them on motorized rollers and use controllers. At some point you should replace those windows though.