In this two-part interview, Moe Hirsch goes deep and wide on buffer tanks and strategies for "parking" BTUs in hydronic systems.

Systems with a high domestic hot water load can also benefit from a buffer tank. You can pipe the domestic hot water tank as its own zone and step down the rest of the structure. However, there will be some standby losses for a tradeoff greater capacity. You also cannot use the buffer tank as an air eliminator or separator; they work only for BTU parking.

Contrary to popular belief, buffer tanks do NOT prevent flue gas condensation. If the buffer tank reaches 120-130 degrees, then it may prevent flue gas condensation via the flywheel effect. Flue gas condensation on boiler systems has to do with excess air, combustion, and run cycle length.

Moe and Bryan also discuss:

• Water storage temperature
• Using a biomass boiler as a backup
• Stratification: tall tanks vs. wide tanks
• Cycle times and mathematical formulas
• Outdoor reset targets
• Boiler startup conditions
• Manual reset high limit