Heat load estimator

This is a steady-state planning estimate, not a manufacturer's sizing calculation. Real heat loss also depends on wind exposure, insulation installation quality, and thermal bridging through the bus's metal ribs — this model adds a bridging allowance and a reserve on top of the base conduction and air figures, but always confirm heater capacity against the unit's own spec sheet at your altitude. See the diesel heater guide for heater selection once you have a target BTU/hr.