Forced air furnace control system and method of operation

Claim 1

Forced air furnace apparatus for heating a building airspace with hot air, including the combination of a furnace having a combustion chamber for combusting fuel to produce hot combustion products which contain CO gas, heat exchanger means in the combustion chamber for normally separating the combustion products from a first air flow path and for transferring heat from the combustion products to heat air within said first path, said furnace having an outlet opening with a given cross sectional area through which air in said first path is directed at a first rate of flow out of the furnace, means connected with said outlet opening for providing a plenum chamber for directing air from the first path along a second path within said plenum chamber, said plenum chamber having a cross sectional area which is sized greater than said given cross sectional area in an amount sufficient to cause air to flow within the second path at a second rate which is slower than said first rate, means for directing air from the plenum chamber along a third path for distribution to the building airspace, control circuit means for switching the furnace between an operating mode for burning fuel to produce said combustion products and a non-operating mode in which combustion products are not being produced, sensor means positioned in the second path of hot air in the plenum chamber for sensing the concentration of CO gas therein and for producing an output signal responsive to the concentration of CO gas in the plenum chamber reaching a predetermined level, and means for operating said control circuit for switching the furnace to said non-operating mode responsive to said output signal.

Claim 5

A method for controlling the operation of a hot air furnace to prevent buildup of dangerous concentrations of CO gas within a building airspace being heated by hot air distributed from an air exit plenum which is downstream in the flow of hot air from the furnace, the furnace having a heat exchanger which separates air circulating through the furnace from the furnace's combustion products which contain CO gas, the method including the steps of controlling the furnace in an operating mode by combustion fuel for producing said combustion products, directing hot air from the heat exchanger out of the furnace through an outlet path having a predetermined cross sectional area while causing the air to flow through the outlet path at a first rate, directing hot air from the outlet path through a plenum path having a cross sectional area which is greater than said predetermined cross sectional area while causing air to flow through the plenum path at a second rate which is slower than said first rate of air flow, positioning a CO gas sensor in the plenum path of hot air while said furnace is in its operating mode, operating said sensor to sense CO gas within said plenum path and generating a disable control signal when said CO gas concentration is sensed above a predetermined level, and disabling said furnace control circuit by switching the furnace responsive to said disable control signal into a nonoperating mode in which said fuel combustion is discontinued.

Claim 6

A method for controlling the operation of a hot air furnace to prevent buildup of dangerous concentrations of CO gas within a building airspace being heated by hot air distributed from an air exit plenum which is downstream in the flow of hot air from the furnace, the furnace having a heat exchanger which separates air circulating through the furnace from the furnace's combustion products which contain CO gas, the method including the steps of controlling the furnace in an operating mode by combustion fuel for producing said combustion products, directing hot air from the heat exchanger out of the furnace through an outlet path having a predetermined cross sectional area while causing the air to flow through the outlet path at a first rate, directing hot air from the outlet path through a plenum path having a cross sectional area which is greater than said predetermined cross sectional area while causing air to flow through the plenum path at a second rate which is slower than said first rate of air flow, positioning a CO gas sensor in the plenum path of hot air while said furnace is in its operating mode, operating said sensor to sense CO gas within said plenum path and generating a disable control signal when said CO gas concentration is sensed above a predetermined level, and disabling said furnace control circuit by switching the furnace responsive to said disable control signal into a nonoperating mode in which said fuel combustion is discontinued.