Abstract: A heater includes a housing having an angled top, a fan having a discharge disposed parallel to the angled top of the housing, and a baffle for laminarizing airflow through the heater. The heater may also create airflow through a cover, across a housing, a heat sensitive component, and/or a raceway, and into a housing inlet. The heater may include a manifold having at least one coupling member that slidingly engages and disengages a burner. Methods for propelling combustion air through a heater, laminarizing combustion airflow in a heater, improving the efficiency of a heater, and converting a heater to make it compatible with a different fuel are also disclosed.

Abstract: The present invention is directed to a sealed vent terminal assembly intended for use in association with high-efficiency oil fired furnaces or boilers. The terminal assembly of the present invention is designed to simultaneously flow outside combustion air to the furnace or boiler and eject combustion gases discharged from the furnace or boiler.

Abstract: A stovepipe thermoelectric generator. The unit fits in a stovepipe of a coal or wood stove. At least one thermoelectric module is sandwiched between a hot side fin unit with fins extending into the flow of exhaust gases and a cold side fin unit with fins cooled by forced room air. A damper controls exhaust gas flow through a heat chamber, directing the exhaust gas through a generating side and a bypass side depending on a temperature indication. This prevents heat damage to the thermoelectric module. At least one fan is provided to force room air through cooling fins of the cold side fin unit An electric circuit is described for providing power for the fan and providing additional electric power for purposes such as charging a battery.

Abstract: The present invention discloses a coupling for use in vent systems which is self-sealing. The coupling includes a gasket in a female part of the coupling that seals against an end of a male part. The female part also including a mechanical locking device that clamps onto a recess in the male part to prevent disconnection. The coupling prevents puddling of corrosive fluids in the coupling at points of metal-to-metal contact and, hence, prevents premature corrosion.

Abstract: A ventilation system for urging flue gases from an exhaust source through an exhaust conduit has an exhaust outlet for venting the gases and an exhaust inlet communicating with the exhaust source. A blower fan is provided for creating a positive air flow away from the exhaust inlet to urge the flue gases through the exhaust conduit and out of the exhaust outlet. A blower pipe channels air from the blower fan into the exhaust conduit past the exhaust inlet so as to create a venturi effect to draw exhaust from the exhaust inlet into the exhaust conduit. Duct work may be provided so that the blower fan draws fresh air from the ambient, namely from outside the structure housing the exhaust sources, rather than from inside the structure.

Abstract: An all weather inlet/exhaust structure (32) for an outdoor furnace (10,12,14) includes a generally rectangular upper compartment (40) having an imperforate upper wall (42) and horizontally louvered, vertical side walls (44) along with an imperforate bottom wall (46) with a generally central opening (48) therein. A lower compartment (56) in the form of an inverted truncated pyramid with its upper wall being defined by the lower wall (46) of the upper compartment is provided. The lower compartment has horizontally louvered, sloped, inwardly directed side walls (58) terminating in an open bottom (60) of smaller size than the first compartment lower wall (46). A generally rectangular inlet air duct (66) depends from the lower edges of the lower compartment side walls (58) and an exhaust duct (26) is disposed within the inlet air duct (66) and extends upwardly through the lower compartment (56) to the generally central opening (48) and the bottom wall (46) of the upper compartment (40).

Abstract: Required blower power in an induced draft combustion system is reduced by recovering pressure from dynamic energy of flow of combustion products. To this end, the outlet duct is diverged gradually, such as an included angle of less than fifteen degrees, and preferably at an angle of substantially seven degrees. Divergence of the outlet duct may be expressed in polar coordinates having a polar axis, overlapping radius vectors and a variable polar angle of such overlapping radius vectors relative to the polar axis. A difference between such overlapping radius vectors is increased in a direction of flow of the combustion products and the outlet duct is structured with cross-sections increasing incrementally in terms of the increasing difference between the overlapping radius vectors. Condensate may be drained from a combustion product by providing the duct with a lateral offset having a bottom extending at an angle to the earth's field of gravity.

Abstract: The pressure pulsations caused by the flow patterns of flue gases entering a flue gas stack from a horizontal duct are eliminated or reduced by the installation of a partition plate in the stack opposite the inlet duct. This negates the adverse interaction of the two vortices in the stack formed by the entering flue gases and allows the vortices to travel independently up the stack.

Abstract: An open fireplace which includes a fuel supporting device (16) that enables the fire (10) to be seen from all directions. An essentially vertical smoke duct (7) is disposed so that its bottom orifice (18) will be located above the fuel. The fireplace includes means (13) for delivering cold supply air in the form of an air curtain which surrounds the smoke from the fire (10) and causes the smoke to pass up through the smoke duct (7).

Abstract: A fireplace vent of the direct-vent type comprises two telescoping sections each having outer air intake housings and inner exhaust housings. One section has an adapter configured to communicate with a standard round concentric vent pipe of a fireplace. The other section has a termination cap. A pair of heat shields are disposed in spaced parallel relationship over the outer intake housing of each section. The vent can be installed horizontally on the fireplace to vent the fireplace through a wall with a minimum of height of an associated window or shelving unit above the fireplace. The adjustable telescoping configuration of the two vent sections also allows for ease in installation by avoiding the need to cut the vent to proper length.

Abstract: A draft hood is provided for mating alignment with a fireplace assembly. The mating alignment is facilitated by the location of alignment hardware fixed to the rear surface of the fireplace and to the inside of the draft hood. In use the hardware permits alignment of the draft hood in a fireplace enclosure without the need to see the fitting, without the need for a long run-in slide, and without the need vertically to pivot the draft hood on installation or to pull the flue termination forward of the firebox flue before attachment. For this purpose an updraft detection warning spill tube may also function as one of the alignment fittings since it is, due to its function, located near or at the junction of the draft hood and fireplace.

Abstract: A vehicle generator has a duct cover for coding the generator body with a structure in which either one of the duct cover or a duct can be adjustably rotated in a circumferential direction of a bracket end and can be attached to the bracket end so as to set an intake vent of the duct at the optimal position in the bracket end, wherein the duct cover has a single shape irrespective of the type of engine the type of vehicle and the arrangement of the engine room in which it is used, resulting in a reduction of cost of fabrication of the generator.

Abstract: Modular discharge structure for closed gas appliances having an inner end and an outer end, comprising: an outer tubular casing; an inner gas exhaust pipe, being placed inside the casing to define an annular supply line for combustion air therewith; a combustion air supply hood, forming a connection between the outside air and the annular supply line, and a combustion gas exhaust hood, forming a connection between the outside air and the gas exhaust pipe, and further comprising retaining means for axially keeping together, in series and in a mechanical and releasable manner, the casing, the combustion gas exhaust hood and the combustion air supply hood on the gas exhaust pipe.

Abstract: A flue insert which includes a helical vane having an open center axial area and means for mounting the helical vane within a furnace flue stack. The helical vane rotates counterclockwise, i.e. it rotates in a counterclockwise direction from the furnace/boiler end to the atmospheric end of the flue. The helical vane rotates for approximately 540.degree., and has a width which is equal to approximately one-third of the diameter of the flue.

Abstract: Flue sections and an airtight venting system being made therefrom by connecting in line the flue sections. The flue section has a pair of opposite ends of circular cross-section one of which called "male end" is shaped and sized to fit into the other end, called "female end" of a similar flue section. The male end comprises at least two outwardly-projecting L-shaped grooves, a peripheral outwardly-opening recess and an O-ring mounted therein and protruding outwardly. The L-shaped grooves are positioned in such a manner to have an opening at the male end of the flue section. The recess is positioned at a distance "H" from the L-shaped groove.

Abstract: This invention discloses a filter-and-fan assembly that can be installed into new fireplaces or retrofitted into existing fireplaces, for filtering dust and smoke out of the hot exhaust gases that are created when wood is burned in fireplaces. This filter assembly is provided with a mechanism that can move the filter out of the flue channel (i.e., the chimney or other exhaust outlet) if the filter becomes clogged by creosote and/or smoke particles. If desired, the mechanism that moves the filter out of the flue path can be automated under the control of a device such as an electronic smoke detector mounted in front of the fireplace, above the fireplace opening. Alternately, a thin filter-paper type of filtering element can be continuously scrolled through the flue channel. A rotating fan blade can be provided directly above the filter element, to ensure that exhaust gases are actively drawn up through the filter.

Abstract: A lightweight, portable cooking unit for use in tents is disclosed. It is designed for use in the mountains, where lightweight equipment is essential. The unit will fit in a backpack when disassembled. The heating chamber has a lower burner unit to hold a common mountain stove burner such as those developed by MOUNTAIN SAFETY RESEARCH. The heating chamber vents to a stack that transmits the combustion gases and moisture safely outside the tent by means of a tent roof jack that protects the fabric from the heat. The stack is also fed with ambient air that mixes with the combustion to cool the exhaust to safe levels. The device can be disassembled and stored in a compact package.

Abstract: An exhaust vent adapter is provided for use in a heating system having a plurality of heating units, which allows all heating units to discharge combustion gases through a single exhaust opening. The adapter comprises a body with a plurality of discrete chambers formed therein, each chamber communicating with a separate heating unit. The body of the adapter has a single exhaust opening formed therein, through which each chamber is independently connected to a separate exhaust vent pipe. The vent pipes leading from plurality of the chambers are concentrically arranged, and may be extended through a single opening in either the wall or ceiling of a building in which the heating units are installed. In a preferred embodiment, the body of the adapter has a single divider secured therein, which defines two chambers and segregates the combustion gases from a pair of heating units.

Abstract: A draft hood assembly and method are provided for installation of a gas fireplace insert to the flue pipe of a fireplace chimney. The insert is for connection between a gas fireplace insert and a chimney flue pipe, the gas fireplace insert having an explicitly-described structure. The draft hood assembly includes a base plate, the base plate having an aperture therein, the aperture being alignable with the exhaust opening which is provided in the upper panel of exhaust channel of the fireplace insert. A hollow superstructure is integrally-mounted on the base plate, the superstructure body being of an explicitly-described structure, but further wherein an upper front plate terminates a spaced-distance above the base plate, and the bottom plate delineates an aperture alignable with the aperture in the base plate. The hollow superstructure body also includes a lower, rear exhaust chamber defined by an explicitly-described structure, which is in gaseous communication with the firebox.

Abstract: A flue insert (50) for insertion into a flue stack (12). The flue insert includes a sleeve (52) that is inserting into the stack so as to function as part of the stack. A vane (54) is disposed in the sleeve. One end of the vane is fixedly attached to the sleeve. The opposed end of the vane is adjustably attached to the sleeve so that after the insert is installed, the overall length of the vane can be selectively set.

Abstract: A through the wall insulated flue for low temperature venting of radiant heat from igniting combustibles produced by wood pellet, kerosene, fuel oil appliances such as stoves and hot water heaters. The flue assembly includes a protective metal tube, housing a ceramic insulated sleeve that is adapted to surround a flue pipe connected to the appliance, with the tube and insulating sleeve being of a length to be journalled through the wall for venting of the radiant heat. An inside wall plate and a complimentary outside wall plate provide necessary receiving collars for the opposite ends of the tube and insulating sleeve and function to correctly position them from internal wall structures.

Abstract: A device for reclaiming waste heat from cooking appliances. The device includes a baffle through which exhaust from the cooking appliance flows, an inlet for receiving exhaust from the cooking appliance, and an outlet for venting exhaust to the atmosphere outside the building or vehicle in which the cooking appliance is located. The baffle extracts heat from the exhaust as the exhaust flows therethrough. The baffle is in thermal communication with a heat sink that directs the extracted heat to the building or vehicle spaces to be heated. The heat reclamation device has a generally thin profile so that the device may be installed above and behind the work surface of the cooking appliance so as to consume a minimal amount of space while not interfering with the normal use of the appliance. The heat reclamation device has means to vent the exhaust directly to the atmosphere, bypassing the baffle.

Abstract: Method and apparatus for controlling grease build-up in cooking vent ducts that includes installing a heat resistant close fitting custom built duct liner and periodically removing, cleaning, and replacing same.

Abstract: A fireplace assembly is disclosed which provides a simplistic assembly technique that enables construction of numerous different fireplace models with a minimum of unique parts. These can be constructed into a desired form without the use of a frame. The internal components of the fireplace are secured to each other in such a manner that a frame is unnecessary. These components are also constructed such that many of them are interchangeable to enable fabrication of various types of fireplaces, such as see-through, cove, island and bay type fireplaces. A pair of combustion dome assemblies, each of which includes an upwardly extending nozzle, creates a significant upward suction within the combustion chamber. This provides superior air flow and combustion together with greater safety.

Abstract: A combination of metallurgical and vent engineering design solutions that result in a superior product, lower installed cost, and corrosion-free performance for venting modern fan-assisted gas appliances by using a flexible, compressible, corrugated gas vent connector. Preferably the connector is constructed from a material having a heat conductivity substantially equal to or greater than aluminum. Other forms of the invention include the use of stainless steel; a double wall corrugated wall in the flex section; and the use of flat flex in the corrugated section.By providing the flex connector with twist lock couplings the connector may be assembled in the field more quickly with a greater assurance of its integrity under adverse conditions such as earthquakes or other building moving conditions.

Abstract: A cover for preventing unwanted fires starting by burning embers of refuse being burned in a barrel is formed by an irregular cone shaped base truncated by a substantially rectangular upstanding tubular throat portion having a rain cap surmounted thereon. The cover is hingedly connected with the barrel for pivoting it to a barrel top open chain arrested out-of-the-way position for placing trash in the barrel.

Abstract: A solid flue cooker is provided and consists of a charcoal burning stove having a firebox and a cooking top, a plurality of legs for supporting the stove, a flue attached to a rear outlet of the firebox and proximate the cooking top of the stove, an oven having a baking compartment mounted to the flue above the cooking top of the stove and a mechanism in the flue for directing and controlling the amount of filtered heated air from the firebox of the stove through the baking compartment in the oven and back into the flue.

Abstract: A fireplace and top wall assembly is disclosed. The top wall assembly includes primary and secondary aligned flue outlet assemblies that form between them a primary air conduit and a secondary flue gas conduit. Both of the conduits are designed to be mounted in fluid communication with the inlet opening of a chimney flue of a fireplace. Flue gases are drawn from the combustion chamber of the fireplace through the secondary flue gas conduit to mix air drawn in by the primary air conduit to promote cooling of the top wall assembly and surrounding fireplace structure.

Abstract: A power vented direct vent system for a fuel-burning appliance wherein a power venter is associated with a vent pipe to create adequate draft for combustion. Outside air is supplied to the appliance for combustion and also communicates through a regulator with the vent pipe for addition to the flue gases. The draft regulator assures adequate draft and can be a barometric draft control. The power vented direct vent system is directly connected to the fuel-burning appliance with complete isolation of the combustion system from the space in which the appliance is located.

Abstract: An aircooled smokestack. The smokestack has passages within it for air or her cooling fluid. The fluid circulates through the smokestack, cooling off the internal and external surfaces. The cooling fluid is then aspirated into the stack gases near the top of the stack, thereby film cooling the upper portion of the interior of the stack. Cooling air is also aspirated into the flowing gases at the top of the stack, thereby cooling the gases as they leave the stack.

Abstract: A stove suitable for large-burner cooking generating a high heat exhaust has an enclosed stove casing with an upper cooking surface, a hollow interior, and a burner well recessed into the interior of the casing. A large burner is positioned in the burner well, and a cooking vessel can be placed over the well so as to close the burner flame off from the outside. The burner well preferably supports a wok or other rounded-bottom cooking vessel. The high heat exhaust from the burner is trapped in the well and entrained by natural convection into a duct member to a duct casing at a rear side of the stove. The duct casing has a double wall construction and baffles in its interior forming a labyrinthine channel for mixing cold air supplied through openings in the stove casing and the hot exhaust air from the large burner.

Abstract: An improved fireplace unit adapted to fit flush within the wall of a dwelling is disclosed. The fireplace unit comprises duct means for ducting cooling air entirely around the inner wall of the unit and especially around the front lateral edges and top, whereby flammable building materials can be brought into close juxtaposition with the unit without substantial danger of fire. Plural ducts are provided for cooling the rear wall of the unit, having inlets at the bottom rear of the fireplace unit, extending upwardly along the rear wall of the unit, and forwardly around the chimney, further cooling this area. The top wall of the unit comprises an integral support member and thermal break which allows the unit to support a conventional chimney without further support structure and provides a substantial thermal break between the chimney and the front wall of the unit.

Abstract: A device for adjustably restricting the flow of exhaust gases in a furnace flue to conserve fuel is disclosed. It comprises two interlocking pipe sections and a helical element having one end fixed to the inner surface of each pipe section. The helical element has a circular opening along its central axis. The degree of restriction provided by the device is adjusted by twisting or separating the two pipe sections.

Abstract: Elongated, vertical air chambers having an open upper end and a closed lower end are located within or attached to the walls of a fireplace, where the upper ends open only into the interior of the fireplace. Air heated within the air chambers rises into the fireplace to increase the drafting efficiency, and is replaced in the air chambers by relatively cooler, draft inhibiting air drawn only from the upper interior of the fireplace. In large furnace applications, the air chambers are located in the lower portion of the chimney.

Abstract: An access door (10) for cleaning grease from duct runs (26) in exhaust systems for kitchen cooking equipment (16). The access door (10) includes a collar (32) which is mounted at a selected location in a run of duct to provide an opening (46) for accessing the interior surfaces (30) of the duct. A fireproof cover (54) is releasably secured to the collar (32) by securing devices for selectively closing the collar opening. A seal (70) is interposed between the collar the cover, proximate the juxtaposed portions to prevent fire from escaping the duct through the collar opening when the cover is mounted thereon.

Abstract: An adjustable fitting for directly connecting a wood burning insert for a masonry fireplace to a vent pipe positioned within a flue liner of the fireplace chimney is made up of an insert connector having first and second legs which are substantially perpendicular to one another. Thr first leg of the insert connector is vertically oriented when the fitting is in place and is sized to engage a flue gas outlet of a wide variety of wood burning inserts. A vent pipe connector completes the adjustable fitting and also has first and second legs which are substantially perpendicular to one another. The first leg of the vent pipe connector is vertically oriented when the fitting is in use and is sized to engage a lowermost end of the vent pipe.

Abstract: A portable heating system operable in three modes; an under-blanket heating mode, a tent heating mode, and a food heating mode. In the under-blanket heating mode, one or more users cover themselves and the basic heater (2) with a light foil-type blanket (68). Air, warmed by the heater, spreads under the blanket thereby enveloping the users so that they are comfortably warm. An adjustable canopy frame (40), in concert with a heat guard (4) enclosing a heat source (6), promotes gaseous circulation under the blanket without hazard. A thermostat (17) automatically maintains the temperature at a safe level. In a tent heating mode, the invention includes an exhaust guide for guiding combustion gases to the outside of a tent via the tent entry. Means are provided for drawing air from outside the tent into the heater for supporting combustion. Means are also provided for the system to adapt to rough or uneven terrain for high stability.

Abstract: An outdoor heating appliance includes a top structure having a top surface, a stationary airfoil, and exhaust openings for flue products. The operation of the heating appliance is rendered wind resistant by generating with the stationary airfoil, in a region above the top surface and in repsonse to wind, an air pressure lower than an air pressure of that wind, and by locating the exhaust openings in that region, whereby the flue products are exhausted from the outdoor heating appliance by the wind. An inlet opening may be provided below the top surface at the airfoil for receiving part of the wind, in order to sustain combustion and generate inside the heating appliance positive pressure toward the exhaust openings by guiding air from the received part of the wind through a channel to a burner in the heating appliance.

Abstract: A furnace roof jack is provided with a pivoting flashing plate which can be attached to pitched roofs having various pitch angles. The roof jack includes an elongated generally cylindrical tube. An enlarged portion of the tube has a generally spherical outer surface. A flashing plate is provided with a hole having a diameter approximately the same as the diameter of the spherical surface. The flashing plate is pivotally attached to the tube on an axis which extends perpendicularly to the axis of the tube along a diameter of the spherical surface.

Abstract: A fireplace and chimney assembly is provided which includes a two wall chimney construction and a termination shield for reducing the amount of cold air which can radiate into a living area. The termination shield encompasses the base of the chimney construction while providing sufficient open area for cooling air to be drawn into the annular space within the two wall chimney construction. A false ceiling is installed above the shield. A firestop is provided therein for receiving the top end of the shield. The assembly prevents cold air from dropping into the chase cavity around the fireplace when the fireplace is not in use.

Abstract: A stove top adapter is provided which is constructed so that a collar is provided on the top side thereof whereby a pipe can be received to be vented through a full masonry chimney in order to achieve a direct connection of pipe from the stove through the chimney to the cap on top of the chimney.

Abstract: A self-adjusting, telescoping concentric flue assembly provides non-separating, substantial flexibility between the telescoping sections of both the flue and the air supply ducts. The lower flue and air supply ducts may move radially independently of each other sufficiently to permit installation even on a furnace having somewhat non-concentric flue and air inlet connections. Attachment of the lower air supply duct to the furnace insures that the lower flue is likewise attached, yet the lower air supply duct can be raised independently of the lower flue to check the connection of the latter with the furnace flue connection.

Abstract: A unique heat exchanger device which is mounted in the flue of a forced air furnace is disclosed. A plurality of copper tubes are retained in a substantially parallel and equidistant relationship by means of end plates. A plurality of circular metallic fins are positioned on the copper tubes and serve as heat radiating surfaces. Cross tubes are provided within the copper tubes permitting the passage of heated air therethrough. The tube assembly is covered by a perforated shroud permitting air at room temperature to pass therethrough and to circulate among the heated copper tubes. An exhaust manifold is provided on the perforated shroud to permit connection of the device to the cold air return on the furnace.

Abstract: A device for adjustably restricting the flow of exhaust gases in a furnace flue to conserve fuel is disclosed. It comprises two interlocking pipe sections and a helical element having one end fixed to the inner surface of each pipe section. The helical element has a circular opening along its central axis. The degree of restriction provided by the device is adjusted by twisting or separating the two pipe sections.

Abstract: A chimney liner system for insertion into a masonry chimney from the top of the chimney down to a stove or fireplace insert. If an offset or a chimney shelf exists in the chimney, a flexible metal pipe member is connected to the bottom end of the chimney liner system. A ceramic heat resistant cloth formed as a sleeve encloses the flexible metal pipe member in selected systems, and in some systems, the sleeve encloses the entire chimney liner system. In some applications, the sleeve may be made from a fiberglass cloth sewn or connected to an inner blanket insulation.

Abstract: A chimney lock attachable to the support plate of a prefabricated metal chimney having vertically downwardly depending cleanouts, the cleanouts being enclosed by an end cap, the lock comprising an adjustable, planer, longitudinal bar removably or rotatably secured to the support plate and positioned to frictionally engage and secure the end cap of the chimney cleanout.

Abstract: A portable heater comprising a double-wall vessel which forms a combustion chamber and encloses a suitable fuel. Air passages provide an airflow through the vessel for supporting combustion. Also included are endless conduits which entrap displaced fuel to prevent it from escaping from the heater through the air passages. Thus, fuel is prevented from escaping from the heater in all positions of the same in the event that the heater is dropped or otherwise upset. A set of cooling fins, encircling a fuel holder, cool the fuel to help maintain an even burn rate. The heater further includes an adjustable flame attenuator for selective heat control. At a low heat setting the invention may be used as a personal or close contact heater wherein an outer wall serves as a guard for preventing contact burns. A modified embodiment of the heater, for use in a tent, includes an air intake tube and a fuel for exchanging gases with the outside of the tent.

Abstract: A vent device is provided for common venting of exhaust gases discharged from separate apparatus at different vent pressures. The vent device provides a passageway and exhaust gas inlets for combining the exhaust gases and conveying them to a single vent stack. The higher vent pressure exhaust gases are discharged within the passageway using a venturi or jet pump effect to provide a zone of reduced pressure in the passageway for inducing the flow of the lower vent pressure exhaust gases into the device.

Abstract: A reflective heat conductor is presented in the form of a grill having a plurality of individual cells bounded by reflective bare metal surfaces. The grill has an arcuate shape complementary to the object, such as a stovepipe, on which it is located. Heat transfer is effected by substantially increasing the conductive area of the surface of the object on which it is mounted, by reflecting radiant heat energy emitted by the surface, and, in the case of a stovepipe, by also increasing turbulence within the stovepipe to reduce stack velocity and produce more complete burning.

Abstract: An in-line power venter insertable into a vent pipe and having a housing attachable to the vent pipe. The housing has separate negative and positive pressure chambers provided by a separator plate positioned within the housing and having an opening for flow of gas to a blower wheel in the positive pressure chamber. The separator plate has a pair of generally semicircular, oppositely-extending sections disposed above the housing for insertion into the vent pipe to positively separate negative and positive pressure zones within the vent pipe. A flow-regulating plate for draft control is mounted within the housing and is manually-adjustable externally of the housing for movement toward and away from an opening in the separator plate to control the flow rate through the opening to the central area of the blower wheel.