[Greenbuilding] Radiant heat/DHW for a 400 SF in-law unit - recommendations?

[Graham Irwin]

I am currently designing a 400 SF in-law unit for a client in San 
Anselmo, CA. It will be build on an insulated slab and constructed with 
SIPs. The roof has excellent solar potential, but the clients are not 
there yet budget-wise though enthusiastic about the possibility. I 
would like to put a hydronic heating system in, and am looking for a 
cost-effective, simple approach, so the combo tankless water heater 
looked appealing - a tankless heater for the DHW is already needed, and 
putting PEX in the slab would be pretty easy and leave the building 
very "solar-ready." The big issue is that many of these systems are 
designed for much larger buildings and we need to control cost, size 
and complexity. The clients are looking at $400-$500 for a direct vent 
gas heater on top of the tankless water heater cost, so I'm hoping to 
spec something that isn't more than $1000 over the cost of a tankless 
heater. Any thoughts or recommendations?

Thanks,
Graham

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