Abstract: A damper assembly is configured for deployment in a forced air duct that supplies conditioned air through a register boot to a register vent secured relative to the register boot. The damper assembly includes a damper unit and a deployment strap. The deployment strap includes a first end secured relative to the damper unit and an opposing second end and has a length that is sufficient to position the damper unit in the forced air duct when the second end of the deployment strap is secured relative to the register boot. When in a deployment configuration, the damper unit has a reduced profile to facilitate deliver of the damper unit through the register boot and into the forced air duct. When in an operational configuration, the damper unit is configured to operate a damper blade between a closed position and an open position.

Abstract: A vent proving system is described for use with a gas fired appliance. The gas fired appliance includes a gas burner, a vent damper for selectively opening or closing an exhaust vent from the gas fired appliance and a relay control for operatively controlling the vent damper and the gas burner to open the damper if the gas burner is on. The vent proving system comprises a sensor for sensing a variable in the vent representing air flow direction in the vent. An electrical switch is connected in series between the relay control and the vent damper. A controller is operatively connected to the sensor, the electrical switch and to the relay control.

Abstract: A damper system comprises a damper blade having open and closed states. The damper blade is movable in a linear direction only between the open and closed states. The damper blade may fully overlap with a flue passage in the closed state, and the damper blade may lack any overlap with the flue passage in the open state. A portion of the damper blade may directly contact a switch activation arm in the open state, wherein the switch activation arm confirms the open state of the damper blade.

Abstract: A boiler including a water jacket surrounding upper and lower combustion chambers for receiving heat for heating water or other fluid therein, which chambers are defined by a refractory structure that extends entirely across the inner casing. A vertical passage through the refractory structure provides for flow of combustion gases from the upper to lower combustion chamber. Oxygen is provided through a first forced air inlet to the upper combustion chamber for burning of wood or biomass, and is provided through a forced air passage in the refractory structure and opening into the vertical passage thereby providing at least one second forced air inlet for burning of the combustion gases and particulates passing therethrough. The refractory structure sealingly engages the inner casing in a manner to seal the upper combustion chamber from the lower combustion chamber so that the upper combustion chamber can be made substantially air tight.

Abstract: A wireless damper control device comprises a damper positioned in a flue, movable between a closed position where the flue is blocked and an open position, a damper controller which sends a damper signal which moves the damper between the open position and the closed position, and a fire side controller which transmits a fireplace signal to open a gas valve to initiate combustion when a fire is desired at a fireplace, and to close the gas valve to terminate combustion when a fire is no longer desired at the fireplace, and which receives a damper status signal from the damper controller indicating whether the damper is in the closed position or the open position.

Abstract: An actuator moves the hinged lid of a cooking grill or similar container between a closed position and an opened position when an electronic sensor detects the approach of a person. For example, the actuator can open the lid when a person approaches, and then close the lid at a later time, such as when the person activates a switch or leaves the area, or after a time interval.

Abstract: An actuator moves the hinged lid of a cooking grill or similar container between a closed position and an opened position when an electronic sensor detects the approach of a person. For example, the actuator can open the lid when a person approaches, and then close the lid at a later time, such as when the person activates a switch or leaves the area, or after a time interval.

Abstract: A draft control system and method can provide for automated control of the air drafting for heating systems. In accordance with an exemplary embodiment, an exemplary draft control system comprises at least one draft plate and a draft plate control system. Draft plate control system can comprise a control unit, one or more input devices, and one or more actuation systems. During operation, the control unit can receive a signal from an input device and use the actuation system to automatically adjust the amount of air intake by controlling movement of one or more draft plates.

Abstract: A draft control system and method can provide for automated control of the air drafting for heating systems. In accordance with an exemplary embodiment, an exemplary draft control system comprises at least one draft plate and a draft plate control system. Draft plate control system can comprise a control unit, one or more input devices, and one or more actuation systems. During operation, the control unit can receive a signal from an input device and use the actuation system to automatically adjust the amount of air intake by controlling movement of one or more draft plates.

Abstract: A damper-controlled gas delivery system for use with gas-fired fireplaces, the system having a solenoid valve controlling the supply of gas to a burner, a manipulable damper control lever, and a wire linkage connecting the damper control lever to a switch that controls the supply of electrical power to the solenoid valve, the damper control lever and switch, thereby preventing operation of the burner unless the damper is open.

Abstract: A chimney flue damper comprised of a generally rectangular frame, a damper flap pivotally mounted to the frame, a bar and extension pin element secured to the bottom of the damper flap and a cable. The bar and extension pin element is rotatably secured to the bottom of the damper flap. When the extension pin of the bar and extension pin element is extended, it passes through an extension pin opening in the damper flap to strike the bottom of the flange of the frame and thus open a damper flap which is stuck closed, either by ice forming on the seal between the damper flap and the frame or as a result of an accumulation of foreign material around the edge of the damper flap.

Abstract: A chimney flue damper comprised of a generally rectangular frame, a damper flap pivotally mounted to the frame, a hammer element secured to the bottom of the damper flap and a cable. A bar of the hammer element is rotatably secured to the bottom of the damper flap. A hammer element head of the hammer element can be pulled away from the surface of the damper flap by pulling the cable downward in the flue. By releasing the cable, the hammer element head will strike the bottom of the damper flap and thus open a damper flap which is stuck closed, either by ice forming on the seal between the damper flap and the frame or as a result of an accumulation of foreign material around the edge of the damper flap.

Abstract: A chimney cap to selectively cover the outlet from the flue of a chimney which includes an open frame of selected geometric configuration located at the top of the chimney flue around the outlet, a cap to substantially cover the opening defined by the frame, bias device to bias the cap to a position separated by the frame, where a seal is provided to seal the cap and the frame when the cap is located contiguous to the frame. A guide arrangement can be provided to guide the cap toward the frame to selectively locate the seal of the cap and seal surface of the frame. A draw device can be provided to pass through the chimney flue to allow the cap to be drawn to engagement with the frame and a latch can be provided to receive the draw device to hold the cap in engagement with the frame against the bias force.

Abstract: The present invention provides a new and useful arrangement for use in a pivotable chimney dampers of the type including a damper flap to selectively open and close the outlet from the flue of a chimney where the damper flap is pivoted and includes bias means to urge the damper flap to a normally open position with respect to a frame which surrounds the flue when the damper is unrestrained and where a flexible connection is provided to be attached at a first location to the damper flap to pull the damper flap to a closed position against the frame member when the pull means is drawn tight. An expansible spring means can be attached between the damper flap and the pull means to be pulled to extended position when the damper flap is closed.

Abstract: A single cavity gas oven and grill unit provided with an oven burner (14) and an independent grill burner (15). A flue (12) has a flap (16) pivotable between a closed position for the oven mode and an open position for the griling mode. The flap (16) is connected by a first linkage to a selector (13) and by a second linkage to a dual gas tap. For the oven mode the selector (13) closes the flap which in turn prevents the gas tap operating the grill. When the grill is on, the gas tap holds the flap open which in turn holds the selector in a position to prevent the oven door being closed.

Abstract: A pre-built fireplace has a housing with an outlet for combustion gases and an open front for viewing the inside of the fireplace. A hinged damper and a hinged lintel extension are suspended from the inside of the fireplace. The damper and lintel extension are pivotally secured to each other so that when the damper is open, the lintel extension is in place to deflect combustion gases, and when the damper is closed, the lintel extension is pivoted substantially out of view.

Abstract: An indicator for a fireplace damper door includes a spiral wire and a contact arm that may engage the wire. The arrangement is such that upon a multiple number of rotations of the contact arm, continual contact is maintained. The arm and wire are is an electrical series circuit with an indicator lamp, which will be illuminated when the damper is opened.

Abstract: A ventilator door and fan control assembly for use with a range hood which is adapted for use in a recreational vehicle wherein there is a plate associated with said ventilation door to open and close the door that is activated by a cable controlled by an operator handle mounted on the range hood within a switch holder and guide. The operator handle and the switch holder and guide are adapted to receive a conventional fan switch and simultaneously activate or deactivate a fan with the opening or closing of the ventilator door.

Abstract: A device for controlling the venting of gases and unburned hydrocarbons from a source location into the atmosphere and includes an enhancement that prevents an entrance of cold drafts and foreign matter in a reverse direction to the source. The device may also be incorporated into a system for venting or distributing air or gases into discrete areas of a residence or commercial establishment.

Abstract: A chimney cover which is hinged to the top of a fireplace flue for opening and closing movement. A mounting bracket is clamped to the top of the flue liner by tightening machine screws against the flue tile without the need to drill holes or otherwise deform the flue liner. A hinge bracket connected with the flue cover is hinged to the mounting bracket by a hinge pin which receives a torsion spring. The torsion spring is loaded in compression to continuously urge the cover toward its open position. A cable extends from the cover through the flue to the fireplace so that the cover can be opened and closed from the fireplace.

Abstract: The invention involves the generation of dry hot steam to be drawn into an oven cooking cavity where the steam is allowed to contact dough pieces on a baking plate in order to bake French bread with a glossy appearance and a hard crust, for example. In one embodiment, the cooking cavity is partitioned in the top thereof to form a steam generating chamber which receives therein a supply of water to convert it into hot steam with the heat from an upper gas burner located beneath the chamber. The upper gas burner and a lower gas burner located beneath the baking plate may be of forced combustion type and a perforated burner tube has provided along the length thereof a flame transmitting member which is divided into a plurality of segments mounted with a proper gap between two adjacent ones thereof to accommodate the thermal expansion of the segmented flame transmitting member and the tube per se.

Abstract: A tool for viewing and opening or closing a fireplace damper system has a bar handle for manipulating the tool and a damper adjustment bar at a fixed angle thereto for engaging the damper and adjusting it with the manipulation of the tool. A mirror unit near the bar joint provides a view of the damper engagement and adjustment. A light preferably illuminates this.

Abstract: A wood or coal burning heater or stove employing a catalytic combustor in its combustion chamber having a primary air supply which feeds air to the fuel, and a secondary air supply which feeds air directly to the catalytic combustor by means of an air diffuser which sprays air evenly over the undersurface of the catalytic combustor. Combustion gases from the burning fuel in the combustion chamber pass through the catalytic combustor to a heat exchanger and then to an exhaust flue. The primary and secondary air supplies are simultaneously controlled so that maximum primary air and reduced secondary air are supplied when maximum heat is demanded, and reduced primary air and maximum secondary air are supplied when minimum heat is demanded. The ratio of primary to secondary air is precisely controlled to maximize overall heating efficiency consonant with high BTU output.

Abstract: The present invention discloses an open gas fire having a gas burner, the combustion products of which are fed to a flue system via a heat exchanger for use in providing heated convection air. In the invention an adjustable baffle is arranged to vary the flow-through cross-section of the path of the combustion products to the flue system, thus matching the flue cross-section to the combustion products quantity, thereby reducing the quantity of cold air drawn into the front of the fire and improving thermal efficiency of the gas fire apparatus.

Abstract: A chimney damper attachable to the top of a chimney flue. The damper is characterized by including a frame mountable to and extending above the chimney flue, a damper plate suspended from the frame, above and in alignment with the flue opening, by an expansion spring, and a vertical stem resiliently attached to the damper plate and extending downwardly therefrom. The stem is mounted to the chimney flue so as to allow vertical movement thereof, and is connected by a cable to a control mechanism mounted in the fireplace opening. The control mechanism, in cooperation with the expansion spring, allows selective movement of the damper plate toward and away from the flue opening to control or eliminate movement of air through the flue. The resilient mounting of the stem to the damper plate allows the latter to pivot with respect to the stem, promoting a tight seal between the damper plate and the flue.

Abstract: Apparatus for supporting a catalytic converter for a burner including a housing having an opening for directing the exhaust gases to a catalyst region and a by-pass opening permitting the exhaust gases to by-pass the catalyst region, a baffle positioned over the catalyst region and having a groove formed in it and a tab extending from one end and adjacent to the groove, a closure movably mounted to open and close the by-pass opening, and a control rod slidably and pivotally mounted within the groove and having one end connected to the closure to open and close the by-pass opening by pivoting of the rod, the rod being lockably engageable by the tab by longitudinal displacement of the rod when in a pivotal position corresponding to closing of the by-pass opening, and having handle means extending from the other end for permitting pivoting and longitudinal displacement of the rod.

Abstract: A damper control is provided which extends the control arm to the lintel. It is a support bracket comprised of a first angle which is secured to the lintel and a second angle which is secured to the first by a set collar and screw. A right angle bell crank is pivotally connected to the support bracket. One end of the bell crank is connected by a horizontal connecting rod, adjustable connecting link and upright connecting rod to the damper control arm. A stop projects downward into the path of the control lever to limit its rotational movement.

Abstract: A fireplace cap includes a pair of hinged doors supported by a rectangular framework of first and second side rails, a header section, and a damper section. The components forming the framework are formed with flanges positioned at the rear of the cap for reinforcing purposes and to act as heat exchangers, picking up heat from a fire within the fire box of the fireplace. This cap can be easily custom fit to fireplaces having fire boxes of various sizes by selecting appropriate components for the framework. A top piece mounted to the header section may serve as a cooking surface. The doors may include optional glass plates supported for easy removal by angle members mounted to the back side of the doors. A latching mechanism, including eccentrically mounted latching arms, holds the doors tightly closed when latched. The top piece and side rails define sealing material receiving pockets and include retainers for holding sealing material to seal the cap against the front of the fireplace.

Abstract: A chimney cap pivotally mounted at one end to allow secure closure of the cap or opening for operation. The lower end of the chimney is connected to a fireplace which has its own manually operated damper. The chimney cap is operable conjointly with the damper or separately by its own operating apparatus.

Abstract: A thermostatically actuated arrangement for controlling opening and closing movement of the damper of a wood burning stove includes a duct arrangement extending through the combustion chamber of the stove between an air intake end opening through the stove housing at a location in the lower portion thereof and a discharge end opening through the stove housing at a location upwardly spaced from the intake end, for passage of ambient air through the duct arrangement for radiant heating thereof during burning of wood in the stove to create a continuous convective flow of heated air from the intake end to the discharge end, and a sensitive bimetallic spring disposed to receive the convective air flow from the duct arrangement at its discharge end and operably associated with the damper of the stove for actuating opening and closing movements thereof in response to decreases and increases in the temperature of the airflow.

Abstract: A novel damper is provided which is attached to the top of a chimney flue for minimizing or altogether eliminating heat losses and air conditioning losses through the chimney flue when the chimney is not in use as well as preventing objects and/or animals from entering into the chimney. The damper comprises a substantially rectangular stamped frame having a central opening and a portion adapted to flatly abut against the top of a chimney flue. The frame further includes at least two and preferably four flanges extending downwardly from the central opening while screws threadably engage the flanges to secure the frame to the top of the chimney flue. A door is pivotally mounted to the frame and movable between an open and a closed position while a spring resiliently urges the door towards its open position. An elongated chain is connected at one end to the door, extends through the chimney flue and is accessible at its other end through a fireplace opening.

Abstract: A damper adjusting mechanism is presented wherein the damper is opened and closed by adjusting a rod. This rod is adjusted by the use of grooves which are latched onto the stove's front wall. These grooves are protected from creosote build-up by a shield.

Abstract: A wood or coal burning stove has an air inlet opening in it which is controlled by a movable closure, a movable front door providing access to the interior fire box, and connecting linkage means which opens the closure when the front door is closed and shuts the closure when the front door is opened.

Abstract: A thermally actuated control system for the chimney flue or vent damper of a hot air furnace employs a fluid reservoir supported in the vent between the damper and the furnace so as to experience the furnace temperature, containing fluid that has a liquid state when the furnace is not in operation and a gaseous state at the higher temperature resulting when the furnace goes into operation. A spring biased piston movable within the reservoir is connected to the damper shaft by a barrel cam supported exteriorly of the vent, which converts the linear motion of the actuator into rotation of the damper shaft. The change in temperature when the furnace goes on or off produces a resultant change in the volume of the fluid within the reservoir, moving the linear actuator between its two positions and rotating the cam and the damper so that the damper is in an open position when the furnace is on and a closed position when the furnace is off.

Abstract: A stove of the wood burning type is provided with a smoke passage having a main opening adjacent the access door of the stove and an auxiliary opening therein which is located further away from the access door and more closely adjacent the rear portion of the smoke passage and the chimney than the main opening. A regulator damper controls the rate of flow of products of combustion from the combustion chamber through the main opening and the smoke passage to the chimney, and an auxiliary damper normally closes the auxiliary opening when the access door is in a normally closed position.

Abstract: A fireplace insert is disclosed which will efficiently heat the interior of a structure, enable control of fuel burn rate and temperature of heated air directed into the interior structure, and facilitate circulation of the heated air through the interior rooms of the structure via pressure differential created by the forced-air flow through the insert. The unit includes an air-tight cover to the interior fireplace opening, a continuous heat exchanger across the top of the fireplace combustion chamber which continues down parallel to the rear of the fireplace combustion chamber and opens rearward to the outside air dual intake chamber which is equipped with a variable speed fan. The interior end of said heat exchanger mates with the forced air outlet in the airtight cover to the fireplace opening.

Abstract: A fireplace stove comprising a generally rectangular metallic housing adapted to extend into a fireplace opening, with penetration being limited by a flange around the housing which engages and seals against the face of the fireplace. A metallic inner fire shell is closely spaced within the inner surfaces of the housing to provide airflow passages between them. An air inlet with a blower is located at the lower end of one side of the housing and a narrow, hot air outlet extends across the top. Air is directed to flow almost completely around the fire shell for maximum heating. An air inlet with a blower is located at the lower end of one side of the housing and a narrow, hot air outlet extends across the top. Air is directed to flow almost completely around the fire shell for maximum heating. An access door is held in sealed engagement by a spring latch and a combustion air duct in the door extends into the interior so that the air entering thereto is preheated before actual contact with the fire.

Abstract: A device intended for flue gas passages includes a pivotable damper plate which is connected to a regulating device for automatic adjustment of the damper plate between a closed position and an open position in response to the operating condition of an installation connected to a flue gas passage. Adjustment is effected with regard to the economical operating position to prevailing outside wind conditions. An anemometric chamber with an associated diaphragm is arranged to be actuated by the gas pressure in the flue gas passage downstream of the damper plate and is connected to the damper plate in such a way that the degree of opening of the damper plate in the economical operation position is decreased for decreasing gas pressure in the flue gas passage.

Abstract: A combined chimney cover and damper comprising an elongated sleeve having a closed end defining the cover and an open end supported within the chimney, support means extending laterally from the sleeve and engageable with the top of the chimney to support and maintain the cover and damper in operative relation to the chimney, at least one aperture in the sleeve between the support means and the closed end of the sleeve, a damper normally resiliently urged upwardly within the sleeve against its closed end to cover the aperture, and means for moving the damper across the aperture to establish communication between the interior of the chimney and the atmosphere. The cover preferably includes a flange spaced horizontally outwardly from and at least partially overlapping the aperture to protect it against wind blown rain and snow.

Abstract: The present invention provides a new and useful safety arrangement for use in a pivotable chimney damper including a damper flap to selectively open and close the outlet from the flue of a chimney. The damper flap is advantageously pivoted to and includes bias means to urge the damper flap to a normally open position with respect to the frame when unrestrained and carried closure means, which can include flexible pull means to be attached at a first location to the damper flap to pull the damper flap to a closed position against the frame member when the pull means is drawn tight where the pull means can be secured to hold the damper in closed position. An expansible spring means is attached between the damper flap and the pull means to be pulled to extended position when the damper flap is closed.

Abstract: A chimney closure is disclosed having a damper which consists of a pair of contiguous generally coplanar leaf sections pivotally mounted over the open end of a chimney. The leaf sections may be pivoted back and forth with respect to the plane of the chimney opening between generally horizontal and vertical positions. One of the leaf sections opens and closes approximately half of the chimney opening. The area of the other leaf section is less than that of the one section and, therefore, it only partially obstructs the remaining part of the opening when the one section is closed. The damper is carried by a casing which surrounds the chimney opening.

Abstract: The specification discloses a kitchen stove hood having two venting modes of operation. The kitchen stove hood is dimensioned to be disposed in a kitchen area over a stove and includes an air intake opening. An air recirculation outlet for recirculating filtered air to the kitchen area and an air vent outlet for venting air from the kitchen area is also included in the kitchen stove hood. A recirculation damper blade is mounted adjacent to the air recirculation outlet and is operable between an open and closed position. A vent damper blade is mounted adjacent to the air vent outlet and is operable between an open and closed position. The damper blades are interconnected by a damper blade linkage assembly which is operable to positively move the recirculation damper blade between its open and closed position while simultaneously moving the vent damper blade between its closed and open position.

Abstract: A prebuilt fireplace construction for installation in a building structure. The construction includes a firebox having an open forward side and an outlet for combustion gases and a housing at least partially surrounding the firebox with the combustion gas outlet extending through the top of the housing. A rotatable damper is disposed within the housing and is controlled externally by a rotatable shaft extending forwardly through the housing which is engaged by an external actuator operable from the front of the fireplace. An inlet conduit for combustion air is built into the housing for the fireplace beneath the level of the firebox for supply of combustion air to the firebox in the event doors are later added to close off the firebox.

Abstract: A control arrangement for a heating system including a furnace having a fuel-fired burner apparatus and a vent stack with a motor driven damper plate for opening and closing the stack, includes an interlock switch which provides a safety interlock between fuel supply valves of the system and first and second limit switches which control the energization of a drive motor for the damper plate and effect energization of the fuel supply valves of the system, permitting the fuel valves to operate only when the damper plate is in the open position and preventing energization of the fuel valves in the event of a malfunction of either of the limit switches. The interlock switch also permits recycling of the system in the event of a momentary power interruption. The control arrangement may include a stack mounted heat sensor switch which interrupts the energizing path for the fuel supply valves in the absence of heat from the main burner within a predetermined interval of time.

Abstract: A control arrangement for a heating system including a furnace having a fuel-fired burner apparatus and a vent stack with a motor driven damper plate pivotally mounted within the stack, includes a stack damper control circuit including first and second limit switches which permit energization of a drive motor in response to a request for heat, premitting the damper plate to be driven to an open position, and for energizing an interlock switch which prepares an energizing path for fuel supply valves of the system, the first limit switch being operated when the damper plate approaches the open position to complete the energizing path for the fuel supply valves prepared by the interlock switch, and the second limit switch deenergizing the motor when the damper plate is driven to the fully open position. The motor is reenergized at the end of the heating cycle to drive the damper plate to the closed position, and the second limit switch deenergizes the motor when the damper plate reaches the closed position.

Abstract: A safety device for butterfly dampers is mounted in the flue duct of oil fired central heaters and operated by a control device susceptible of rotating a damper element actuated by the pressure of fuel oil fed by a pump through an oil supply line to a burner head to open and close the flue duct. A valve device is mounted in the oil supply line between the oil pump and the burner head and controlled by a position indicator associated with the damper device. The rotation of the damper element is transferred to the position indicator who relays the signal to the valve device. Accordingly a rotation of the damper element toward the closing position will actuate the valve device to close the oil supply line and extinguish the heater.

Abstract: A cap-type flue damper mountable in the flue opening, the cap position relative to the flue opening being controllable from controls located at the hearth, the damper having a built-in brake which prevents the cap from closing in the event of a malfunction in the spring urging the cap in the open position.

Abstract: A mechanism for mounting within a firebox of an existing fireplace to control the opening and closing of a pivotally mounted flue damper plate. A vertically extending connecting rod is connected at its upper end to the damper plate. An L-shaped control rod is eccentrically connected to the lower end of the connecting rod adjacent the rear of the firebox for vertically moving the connecting rod upon rotation of the control rod. The control rod is rotatably mounted on and extends beneath a usual fuel holding grate supported on the floor of the firebox. The front end of the control rod extends upwardly in front of and above the grate when the damper is in closed position obstructing placement of fuel on the grate and lighting of a fire therein and providing a visual indication that the damper plate is closed.

Abstract: A damper designed to close the top of a fireplace chimney provided with a spring urging the same open and a second and stronger spring attaching the damper to a cable which extends down the chimney for purposes of opening and closing the damper, a lever being provided in the fireplace for locking the damper in either open or closed position, the damper being attached to the top of the chimney flue by means of an adjustable bracket.

Abstract: An air heater for installation in a fireplace located in a room to be heated having a lower metalic portion having a hollow back wall surmounted by a flue portion also having a hollow back wall communicating with the hollow back wall of the lower portion so as to form a common heating chamber. The heating chamber has an opening at its lower end for receiving air to be heated from outside of the room in which the fireplace is located and has a plurality of ducts extending across the flue portion at the upper end of the heating chamber for permitting escape of the heated air into the room to be heated and a vent pipe extending from the upper end of the heating chamber to vent heated air outside of the room in which the fireplace is located. The air ducts and vent pipe are opened and closed by the operation of valves so arranged that when the air ducts are opened to the passage of air the vent pipe is closed and the vent pipe is open when the air ducts are closed.