Monterey PLUS HIGHER-EFFICIENCY gravity, top-vented wall furnaces require no electricity for operation, a matchless pilot igniter and automatic temperature and safety controls. The furnace is vented through the roof to the outside (venting material not included) and requires installation on an interior wall. Designed to heat two adjacent rooms (25,000 Btu/hr. on each side) operating with a single thermostat. 71% AFUE.