PA seven-node thermal network program, developed for simulating the performance of passive buildings on a programmable calculator, is described. The computational algorithm is outlined, input and output format are indicated, and the results of a validation test are presented. Applications are illustrated by three case studies:

1. designing a central mass core in a direct gain house,
2. sizing a blower and rockbed for a passive house, and
3. comparing concrete and water walls in a freestanding greenhouse.