The standby loss and recovery efficiency of a test heater are predicted based on a semiempirical model and compared to actual test results. For one case, the computer simulation predicts a standby loss of 3.6% per hour, compared to a value of 3.9 obtained using a standard test procedure. Likewise, a recovery efficiency of 75.9% predicted with the computer simulation compared favorably with a measured value of 76.5% obtained with the test heater.

Using the computer simulation derived from the model, the effects of certain design changes to the test heater were predicted. In particular, the influence of different insulation thicknesses, automatic ignition, and flue dampers are considered.

The model relies on general heat transfer relationships between the stored hot water and the ambient air, internal flueway, and combustion chamber. It should be applicable to gas water heaters similar in geometry and construction to the test heater. It is limited, however, in that it assumes a uniform temperature of the stored water, neglecting the possible effects of thermal stratification on daily energy consumption.