The bigger, the better – as a general rule: a buffer tank can never be too big. More buffer capacity always means fewer boiler starts and therefore a longer system life expectation, lower energy costs, and greater comfort.
Unfortunately, not every boiler room has unlimited space. Therefore, this guide explains the minimum buffer tank size required for efficient heating system operation. For log boilers, this calculation depends on the amount of fuel the boiler can hold, i.e., the filling chamber. For automatically fed boilers, such as pellet or wood chip boilers, the minimum buffer tank volume is designed for half an hour of full boiler operation. Furthermore, the required buffer tank volume for both automatically and manually fed boilers depends on the temperature difference (or spread). This refers to the difference between the boiler's flow temperature and the return temperature at the point of use. A higher temperature difference means only a small amount of water needs to be heated and circulated. This saves energy – and in this case, the buffer tank can be somewhat smaller.
A simple rule of thumb applies here: Boiler capacity x 10 = minimum required buffer volume. Boiler capacity x 15 = optimal buffer volume for best energy efficiency and ideal comfort.
ETA-tip:
Especially with high-quality firewood such as beech, for operation during the transitional seasons, for hot water preparation in summer, and to keep the refueling intervals as long as possible, even larger buffer tanks are recommended.