boiler/ondemand/waterheater - which one???

Rodney Summers

Weil-Mclain CGA-25 is 38,000 IBR output.

MJ

I am renovating a 1945 cinderblock, slab-on-grade, 1100sq ft. long, narrow, rectangular ranch. This will include a "T" shaped addition - slab on grade, 1500 sq ft. Please see attached layout. The new section will have shallow frost protected foundation made with ICF's, walls made with SIP's, shed green(planted) roof made with truss and 2 x 12's. It also includes an open two story connecting room (the bottom of the "T") 24 x 16 that is used for passive solar and convective cooling. So we have existing footprint with low energy efficiency and insulation value and new footprint that is highly energy efficient and high R-values. Already looking into venn aire systems for recovery.
I am removing the existing forced air gas furnace in the existing. The new will be all infloor radiant. The old kitchen can have infloor but the rest has nice hardwood on sleepers that I do not want to pull up. The utilities are being relocated from the existing laundry area (which will become part of kitchen) to the existing attached garage (which will be insulated and radiant infloor). The existing bathroom is at the complete opposite end of the house with under slab hot water supply that we can't locate and in attic cold water supply.

So......finally my dilemma!
In order to relocate the heating system, I still need to get hot water and either baseboard or hydro air over to the existing living, 3 bed and bath PLUS feed the radiant for the new PLUS feed the radiant for the old kitchen and garage area PLUS maybe some day add solar PLUS keep humidity at proper levels for SIP's. If I use pex tubing for supply lines to bath they'lll have to go through attic. Should a boiler provide all OR should I put on demand at point of bath and 3 bed and use hydro air or baseboard from it and then keep water heater for radiant of new plus potable water source for kitchen? Or, should I use on-demand in new bath and feed radiant from it for entire addtion and keep water heater for existing potable and baseboard or hydro air system?

I know this is alot of questions but I am not sure which is better. Also, I did a heat loss calc and came up with 36,600, BUT I have ordered the one from this site and will redo it to verify accuracy when it arrives.

Alan(OnVacationInOregon)Forbes

Small load

That's a small load and if it weren't for the hydro air and baseboard, I'd say to use a water heater for a combined DHW/radiant system. But you need high water temperatures.

Anybody got any ideas? Why doesn't anyone make a low BTU (under 50,000) boiler that's relaible? Seems to be a big demand.