A typical indirect water heater is a tank with a coil inside it, where the domestic (potable) water resides in the tank and the submerged coil connects to a hydronic heating boiler, operating as a separate zone. A personal favorite of mine, it offers the following advantages:
- Quick recovery
- Superior hot water production
- Efficient operation
- Lifetime tank warranty (most models)
Another HUGE benefit is that it keeps the hydronic boiler cycling throughout the summer months, exercising components and minimizing breakdowns due to five-month shutdowns.