a gas heat pump system powered by natural gas , propane or similar gaseous fuel is disclosed . the system uses heat recovery and heat addition to manage efficient heating and cooling cycles . in a cooling cycle excess heat is vented to the atmosphere while in a heating cycle , excess heat is used to heat a subject structure and to prevent frost from forming on outdoor heat exchangers . a control system monitors the system &# 39 ; s operation and corrects abnormal operational conditions or shuts down the system until the system can be manually inspected . the costs of system operation are less than electric systems because of the efficiencies and use of natural gas or propane .