Gas and oil heating appliances generate heat through the combustion of fuel. The heat is transferred through the heat exchanger and distributed to the conditioned space. The products of combustion, however, must be vented safely out of the structure. In a conventional chimney, venting is achieved by the natural lifting action of the hot combustion gas. New, efficient systems absorb more of the heat in the heat exchanger and produce lower temperature vent gas. Lower temperature gas does not rise as quickly or as reliably as in older, less efficient systems. Power venting or sidewall venting is more economical and safer than chimney venting. A power venter uses a motorized blower to vent the products of combustion. A power venter is interlocked with the appliance to ensure that proper draft is achieved before the appliance burner is activated.