Short operating cycles continue to be one of the chronic complaints associated with modern hydronic heat sources. Even state-of-the-art mod/con boilers with 5:1, 8:1 or even 10:1 ratios between their maximum firing rate and minimum stable firing rate can’t always match the heating load imposed by a single small zone, such as a towel warmer radiator in the master bathroom, on a mild day. This is where the additional thermal mass provided by a buffer tank provides the “thermal elasticity” needed between heat supply and heat demand.
Over the last couple of decades, the North American hydronics industry has been learning the importance of buffer tanks as low thermal mass boilers, and water-to-water heat pumps have been increasingly combined with highly zoned distribution systems.