Why does the web-based calculator assume that a wood-fired boiler would be half the size of my existing boiler?
In general, fossil fuel boilers are sized to meet peak load conditions which occur infrequently and for very short durations (such as for 15 minutes every five years). If a wood-fired boiler were to be sized to meet the peak load condition it would frequently operate in low and medium fire conditions. Unlike fossil fuel boilers which modulate well between high, medium, and low fire, wood-fired boilers perform most effectively in high fire mode. By reducing the size of the wood-fired boiler, it will operate in high fire mode more often. An energy model should be developed to determine the optimal size of the wood-fired boiler. Generally, this size meets 90-95% of a typical heat load. Existing fossil fuel boilers can be used to meet low load and peak load conditions as necessary.
