Combustion air vent control for furnaces

Abstract

Various apparatus are disclosed for controlling the combustion air vent of fuel-fired furnaces. For a first embodiment of the invention, a furnace-controlled air valve is placed in the combustion air duct. When the furnace begins a heating cycle, the valve is opened. When the heating cycle ends, the valve is closed and remains closed until the beginning of the next heating cycle. For a second embodiment of the invention, a positive-displacement air pump is placed in the combustion air duct. The air pump pumps air from the exterior into the mechanical room at a controlled rate during each heating cycle of the furnace. The air valve or the air pump is controlled directly or indirectly by the furnace thermostat.

1 . In combination with a fuel-burning furnace controlled by a thermostat, said furnace being installed in an enclosure located within a habitable structure and requiring a duct for admitting combustion air from outside the structure into the enclosure, a duct control device comprising:
 an apparatus having a first state which blocks the flow of combustion air through the duct and a second state which allows the flow of combustion air through the duct; and   a control apparatus which establishes and maintains said first state during periods between furnace heating cycles and establishes and maintains said second state during furnace heating cycles.   
   
   
       2 . The combination of  claim 1 , wherein said apparatus is a valve having a movable control element which either closes the duct when in a first position corresponding to said first state or opens the duct when in a second position corresponding to said second state, said movable control element operating under the control of said thermostat. 
   
   
       3 . The combination of  claim 2 , wherein said valve is selected from the group consisting of balloon valves, flapper valves, ball valves, and butterfly valves. 
   
   
       4 . The combination of  claim 2 , wherein said movable control element is moved between said first and second positions by mechanical actuators selected from the group consisting of an electromagnet in combination with a spring, an electromagnet in combination with gravitational force, DC electric motors and AC electric motors. 
   
   
       5 . The combination of  claim 1 , wherein said apparatus is a positive-displacement pump which prevents combustion air from flowing through the duct when in said first state and pumps combustion air through the duct when in said second state. 
   
   
       6 . The combination of  claim 5 , wherein said positive-displacement pump is selected from the group consisting of sliding vane pumps, flexible vane pumps, external gear pumps, internal gear pumps, Roots-type pumps, and rotary lobe pumps. 
   
   
       7 . The combination of  claim 5 , wherein said positive-displacement pump is powered by electrical current that is controlled by a switch that, in turn, is controlled by said thermostat. 
   
   
       8 . The combination of  claim 7 , which further comprises a transistor to which is applied a control voltage corresponding to an output voltage from said furnace thermostat, and wherein a high level control voltage causes said transistor to transmit power to said switch, thereby turning it ON, and a low level control voltage causes said transistor to cut power to said switch, thereby turning it OFF. 
   
   
       9 . The combination of  claim 5 , wherein said positive-displacement pump is powered by an electric motor selected from the group consisting of DC and AC motors. 
   
   
       10 . In combination with a fuel burning heating device controlled by a thermostat, said heating device installed in an enclosure located within a habitable structure and requiring a duct for admitting combustion air from outside the structure into the enclosure, a duct control apparatus comprising:
 means for blocking the flow of combustion air through said duct during periods between furnace heating cycles; and   means for allowing the flow of combustion air through said duct during furnace heating cycles.   
   
   
       11 . The combination of  claim 10 , wherein said means for blocking and said means for allowing is a valve having a movable control element which either closes the duct when in a first position or opens the duct when in a second position, said movable control element operating under the control of said thermostat. 
   
   
       12 . The combination of  claim 11 , wherein said valve is selected from the group consisting of balloon valves, flapper valves, ball valves, and butterfly valves. 
   
   
       13 . The combination of  claim 11 , wherein said movable control element is moved between said first and second positions by the combination of an electromagnet and a spring. 
   
   
       14 . The combination of  claim 11 , wherein said movable control element is moved between said first and second positions by the combination of an electromagnet and gravity. 
   
   
       15 . The combination of  claim 11 , wherein said movable control element is moved between said first and second positions by an electric motor selected from the group consisting of DC motors and AC motors. 
   
   
       16 . The combination of  claim 10 , wherein said means for blocking and said means for allowing is a positive-displacement pump which operates under the control of said thermostat. 
   
   
       17 . The combination of  claim 13 , wherein said positive-displacement pump is selected from the group consisting of vane pumps, flexible member pumps, external gear pumps, internal gear pumps, Roots-type pumps, and rotary lobe pumps. 
   
   
       18 . The combination of  claim 13 , wherein said positive-displacement pump is powered by an electric motor selected from the group consisting of DC and AC motors. 
   
   
       19 . The combination of  claim 10 , wherein said means for blocking and said means for allowing are directly controlled by electrical power passing through a switch that is controlled by a signal generated by said thermostat. 
   
   
       20 . The combination of  claim 10 , wherein said switch is selected from the group consisting of solenoids, bipolar junction transistors, junction field-effect transistors, and insulated-gate field effect transistors.