Hesperus, I thought I would go geo thermal in the beginning but I'm just not sure right now. Kinda leaning towards just a high efficiency propane unit. I like the idea of domestic hot water also. Is there a general rule of thumb on how far you can go to a separate out building?
Geo is not for everyone no doubt about it. Our Geo has a "desuperheater" that circulates warm water through the water heater. The theory behind it is sound, but in practice it needs a bit of alteration in my opinion. Basically, I consider it ineffective if your water heater actually works. You are circulating warm to hot water through a tank that is already hot. What we did here was install a Marathon (all poly) water heater as a buffer tank and left the elements off. The desuperheater warms the water in this tank as needed. This warm water goes to the Takagi tankless that kicks it up to 119°f for delivery.
How much domestic hot water do you need? The TT with built in only has a 14 gallon tank so it's not a whole house deal. If you want to make full family DHW from the boiler you would the solo unit and an indirect fired water heater unit. The boiler will make the hot water and a relay control will direct where it goes. You'd essentially either circulate hot water through the unit, or the floor system. These are very efficient and very quick recovery as well. If you go indirect I have a 30 gallon Bock unit here brand new in the crate. A 30 gallon indirect will deliver on par with a 50 gallon conventional.
As far as distance, I'd say a few hundred feet. If you insulate proper it's not too bad to move hot water.
