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Publication numberUS2521866 A
Publication typeGrant
Publication dateSep 12, 1950
Filing dateSep 9, 1946
Priority dateSep 9, 1946
Publication numberUS 2521866 A, US 2521866A, US-A-2521866, US2521866 A, US2521866A
InventorsOran W Ott
Original AssigneeOran W Ott
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Air-heating furnace with automatically controlled air by-pass for preventing condensation
US 2521866 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

Se t. 12, 1950 o. w. on 2,521,366


5 Claims. 1

My invention relates to air heating and more particularly to a combustion-type heating unit ofthe forced air type for heating a stream of air in controlled amount for delivery directly or indirectly tothe interior of a building.

Space heating is often accomplished by forcing a stream of air between passaged heating elements conducting hot products of combustion from' a suitable burner to aflue. The heating elements are conventionally thin-walled units,-

often formed of sheet metal, heat being transferred from the products of combustion to the airthrough these walls. It has been found that thes'ewalls are subject to corrosion and scaling with continued use and that the scale tends to.


'Co'ntrary to early belief that such corrosion waslth 'resultof using fuels containing sulfur or otheracid-formin substances, it has now been found "that it is the result of the inevitable moisture inthe products of combustion. So long as the'='products of combustion are maintained at a temperature above the dew point, the water rezna'ir'is in vapor state'and no serious corrosion is encountered. If, however, the Water is allowed to condense inthe passages of the heating elements or in the bonnet or vent outlet into which the products of combustion discharge, the'condensate will corrode the'walls and often the burners if permitted to drop thereon. The corrosion is due partly to a rusting action and partly due to the fact that the condensate cone, tains carbon dioxide, extracted fromthe productsof combustion, which produces a highly corrosive; weakly acidic hydrocarbonic gas solution. ZI -It i's' an'object ofv the present invention to pro-' vide a novel heating unit which maintains the products' of'combustion above the dew point and,

above-mentioned corrosion dif- A further object is to provide an outer pas-. sage means for heating and an inner passage means for the by -pass function.

Another object is to. employ at least twoheating passages spaced from each other to pro-, vide a by-pass passage th'erebetween. In one" embodiment of the invention it is an objectlto provide additional by-pass passages on the outersides of the heating passages to separate them. from other heating passages or from a wall of the heating unit.

It is another object of the invention to pro-- vide a simple, easily actuated damper arrangement for varying the relative volumes of air flowing through the heating and'by-pass passages. In this connection, a more SPBCifiC'Ob. ject is to dispose a shaft or operating member transverseh of the heatingand by-pass passages, this member carrying damper members: respectively in the streams moving through the heating and by-pass passages. Another object. is to employ one or more of such shafts or operating members and control the position thereof to vary the temperature of the composite. stream. In this way the air throughput of the heating unit or the output velocity of the air can be maintained substantially constant even with change in heat demand of a thermostat, a very desirable situation particularly where a desiredcirculation is to be maintained in a room regardless of changes in heat demand to maintain a desired room temperature.

A further object of the invention is to provide a simplified control system for such a heating unit, in contradistinction to many recently used control systems which exceed in cost the heating unit itself.

Still a further object is to provide a cheap, highly efficient, simple and trouble free heating unit which can be adapted to use as a unit heater, duct heater furnace, etc.

Further objects and advantages ofthe invention will be apparent to those skilled in the art; from the following description of three embodiments which are presented as exemplary.

Referring to the drawings:

Fig. 1 is a vertical sectional view of a duo heater embodying the invention;

Fig. 2 is a horizontal sectional view taken along the lines 22 of Fig. 1, Fig. 1 being taken along the line il of Fig. 2;

Fig. 3 is a transverse sectional view taken along the line 33 of Fig. 1;

Fig. 4 is a horizontal sectional view, similar to that in Fig. 2 but showing an alternative embodiment of the invention; and v Fig. 5 is a side 'elevationalview, with parts broken away to show internal construction, of a unit heater embodying the invention.

The embodiment of Figs. 1-3 is a duct heater, generally indicated by the numeral 10, and adapted to be disposed between duct sections 3! and I2 through which a stream of air is moved by a remote blower, not illustrated, the direction of air flow being as indicated by the arrow iii. The d-uct heater duct sections H and I2 and mountedthereto as by flanges 16. In the embodiment shown; the duct sections H and I2 are rectangular in cross section, the housing 45 providing upper and lower walls 11 and i8 and two side-walls i-S and-ZU,

The up-stream end of the housing i provides an entrance chamber 22 receiving the air stream. Vertical partitions 23 and 24, extending between the upper and lower walls I! andqtfl; divide the down-stream interiorbf the; housing 15 into: an outer passage means, comprising heating passages 25. and 26", and an inner? passage -means, comprising-a by-pass passage 21; The main stream of air; flowingas indicatedcbythe arrow I3; is

divided by the partitions 23' and2 3' to: form three sub-streamsfiowing respectively" through the passages25; 2mm 21 and'mixing or. blending'therebeyondimauexit chamber 28, formed by the duct" section 12 of the housing 15, to formacompositestrea-m flowing as indicated by arrow29; A deflector'3ii, aided by directional'louvers 3! on each side thereof; dividesand deflects the-sub-stream H3 provides a conduit-like housing l5 shaped and sized to correspond to the trolling the sub-stream movin through the bypass passage Z'i. The primary and auxiliary damper means are preferably interconnected so that one closes while the other opens, all in response to change in temperature of the exit products of combustion.

The preferred damper means and control therefor is clearly shown in Figs. 1, 2 and 3. As there shown, a plurality of operating members or shafts- 55: have their ends journalled in the side wallsi9 and 29 to extend in parallel relationship across the heating passages 25 and 26 and the by-pass passage 27. Each shaft carries two primary damper members 51 and 5B, respectively in the heating passages 25 and 26, and one auxiliary damper member 5E! disposed in the by- I can be a bar; 6s pivoted to'the ends of the damper moving-through the bypass-passage 2'! to move same outwardly" toward the other sub streams; thus. aiding; in the mixing or blending. thereof.

The heating passages 2-5 and it; are, in eiiect,

a part of two heat-exchange units or heating" sections 33 and $46 which serve to heat thesubstreams flowing therethrough; the sub-stream flowing through them -passpassageE'l being substantially unheated. Eaclr heating section provides. a plwality' of heating elements -3-5-. spaced from each other to pass the air, each heating: elementproviding an: internal upright passage 36'.v The heating: elements; are shown as extending between the upper and lower walls H- and- I8, which walls are apertured to permit-thein--- ternalrpassages 35' to: communicate openly with a; vent space or bonnet 38' and'a burner space 3%.

These spaces are formed between front and rear;-

walls 49? and t t ofrthe heating; unit I Bend are enclosed bylongitudinal'walls'idz Aasuitable'burner means, shown asa gas burner M= fedi by a supply pipe-d5: equipped with a suit,- able air-mixer 4G and receiving air through ports 4,1;is disposed in the burner space 39. The hot products of combustion rise through the passages 36, heating the walls thereof and:v thus the adjacent air streams: The proddctszofrcombustion= enter the bonnet 38 and are discharged through a suitable vent d8;

During continuedzoperation of. the heating unit ID it is desirable that theproducts of combustiom streams movingthrough the heating passages 25- and-16, and an auxiliary damper means 52cm- In general,

members 53 toinsure equiangular movement oi?- all of theshaf-ts 55-. r

Preferably, the damper means should becon-- trolledby the temperature of the productsofcom-'-= bustion issuing from the passages 36. This canbe accomplished by disposing a fiuid fille'ct. thermany-responsive bulb 62 in the bonnet- 38/and: connected to. a suitable fluid-operated motor. 63."

mounted'on the topwa-ll' l1. As thebonnet temperature decreases toward the dew point, thecom ing action on the products of combustionwhile,

tracting-fluid moves an arm 64 of the-:motorx63 in a counter clockwise directionto-movethe' pri,-= mary' damper means 58 and 5| toward closed po,-- sition, while simultaneously and correspondingly moving the auxiliary damper means 52. toward open position; decreases the air flow through theheatingpassages to decrease thezcoole correspondingly increasing the volume of bypassed air; The oppositeefiect takes place if the. fluid expands as a-result of excessive-bonnet tem-' perature. The operative connection between the: arm 64- and the damper means may take-any one of a number of forms, being shown as a. linlrti pivoted to the arm and to the uppermost damper member 58,

If a thermostatic temperature-control is desired,

noid: l l',, assuming a completely open position:

when the solenoid is energized and a partially openv or minimum position when the solenoid is deenergized. Such actuation is efiected'bybpening and closing. of the contacts of a thermostat 12' subject to the temperature of the room being. heated. Such contacts are connected in series" with the winding of the solenoid I l, with thesesondary winding of a transformer T4, andiwithia master control switch. Also connected across? the secondary winding beyond the controlrswitch is a solenoid It of a: normally-closed shut-0115" essences;

valve in the supply pipe 45. Closing the control switch opens the shut-off valve 11 and moves the valve-10 to maximum-open position, assuming that the room temperature is low and the thermostat'l2 is calling for more heat. When the temperature rises, the thermostat 'deenergizes the solenoidll and the valve 19 moves to partiallyopen position to retain the burner 44 lighted and supplying insufficient heat to fill the demand. In this 'way theheating unit l delivers air at two elevated temperatures during continuance'of a substantially constant air flow into the roomto maintain the desired circulation. To shut off the system or to use it merely to circulate air, the switch 15 is opened to out off the fuel supply by closingthevalve TI. During thermostatic variations in fuel supply the temperature of the products of combustion in the passages 35 will vary. However, the damper means and the control therefor will oper ate to maintain the temperature of the productsat combustion above the dew point to prevent condensation of moisture and consequentcor rosion, While'the damper means 59, and 52 have been illustrated as within the entrance portions of their respective passages 25, 25 and 2l, this arrangement is not essential as the damper means can be positioned at any point where they will control the sub-streams. The illustrated posi tioning is,however, preferable asit prevents air from entering and swirling in the heating passages ahead of the control zone as would be the case if the damper means were disposed toward the'exit' ends of the heating passages.

While the invention contemplates that a single large damper member. can be used in each of the passages 25, 26 and 2l,'the damper members being one; common shaft, it is preferable to employ face dampers of the plural-member type, as shown. The air distributionand accuracy of control is battered by such use of face dampers.

An important feature of the invention lies in the interposing of a by-pass passage between heating sections. This produces a'compact unit, gives better control and permits use of the simpli-' fi'eddam'per' means and control illustrated.

Itshouldbeunderstood, however, that all of the by-passed air need not move through a single centralpassage. Thus, Fig. 4 shows an arrange ment similar to thatof Fig. 2 but with additional partitions 8B and-8| spaced from the side walls l9 and 29 to form additional by pass passages 82 and 83. The-central by-pass passage 2'! is narrower than in Fig.2; but it, together with the additional by-pass passages 82 and 83, serves to .by-pass the desired amount of air. In this embodiment two additionalauxiliary damper'means 84 and 8 5 are employeiicomprising damper members 86 and 81 mountedbn each shaft 55 and positioned in the by-pass passages 82 and .83. This embodiment has ;,the additional advantage that the substreams moving through the by-pass passages-82 and 83" are positioned immediately inside-,the housing [5 thereby maintaining the walls l9 and 2B vcoolu In Fig. 5 the invention is illustrated as embodied in a unit heater 90 of the type adapted to be suspended near the ceilingof a room. The internal construction, including. the heating passagesand by-pass passage, is identical with the, embodiment shown in Figs. 1-3. Likewise, the" damper. arrangement is identical, the damper means 5| and its damper members 58 being shown in Fig, 5. However, inthe embodiment of Fi'g'r5' the:- entrance chambers22' "contains a fan 9| 'drivenxby a 'motor'92 secured to the housing l5 by: a suitable bracket, not shown. The link is pivoted to the lowermost damper member 58 and the arm 6| is pivoted at 93, being actuated by a thermally-responsive device 94. positioned in the air stream drawn into the inlet chamber 92 by the fan 90, being thus responsive to'room temperature. 1 x

In .theLAembQdiment of Fig5xthe three substreams moving respectively through the heating passages 25,1-26'and the by-pas's passage 21 im-" pinge 0n deflectors 96 which aid in the mixing of thefcomponent streams while deflecting samedownwardly 'intoithe room. In this embodiment theburner 44 may be constructed as previously described but'the air-mixer 46 is positioned outside the housing IS. The fuel supply pipe 45 contains the previously-mentioned shut-off valve 11 and'its solenoid 215, which may be energizedz simultaneously with the motor 92 to open when the fan'is set into'operation.

"However this embodiment includes an addi-fl tional; control-valve 95 in-the fuel supply:pipe 45. and controlled by athe thermally-responsivedevice 94. The valve 95is a flow-modulating valve, typicallya v globe valve or a gate valve which'open's and closes. incremently in response to temperature changes afiecting-the. thermallyresponsive: device 94.. As illustrated, this thermally-respo'nsive device 9'4gincludes a rod 96 carryinga pin 91'extending into a slot 98 of the arm 6L:- The rod96 is a part of or is connected: to-a valve stem 99 of the valve 95. 1 The-control arrangement is such that the rod; 96 movesrespectively upwardly and downwardly in response to increase and decrease in room tem-y perature. Thus, ifthe room temperature increases above the desired point, the rod 96- will be; lifted. This will have. two actions. In the first place, it will move the valve 95 toward closed position thus throttling the fuel supply to the burner 44'. In the second place, it will pull downwardly on the'link 65, thus tending to close the I 7 primary ,dampergmembers 51 and 58 to restrict the ,air. flow through the heating passages 25. and 25 whileisimultaneoi ely. opening (the auxiliary damper members59' to increase the, air flow through" the icy-pass passage 21. As' a c onse' quence, the amount ,of air flowing through the heating'pas'sages fi 'and25 is reduced simultaneously with the temperature of the products ofl' ombustion rising in the internal'passages 36 of the heatihg'elem'ents '35. By proper correlation ofthe damper means and thevalve 95, the" products of combustion will never be cooled below the dew point,

, With this arrangement, it will'be evident that there will be a differential change in'the volumes" of theair streams moving through the heating passages 25, 26'and the 'by-pass passage 21. As a consequence, the temperature of the combined streams will vary from time to time as the heat demand changes. apparent that the total volume of air issuing from the heating unit will be substantially constant and independent-of heat demand. This is very desirable as the exit air stream will maintainthe desired circulation of air in the room. This is in contradistinction to those heating systems in which; the unit iscontrolled to supply hot air to the room intermittently in response to a thermostatic control which turns the fuel supply completely on or completely off.

; wan exemplary embodiments of the invention At the same time, it will be" agsansoea sain -passages providing inlet; ends. communioa'tingiwith each other and" exit ends=communieat=- ingi withz each other; means. for flowing: three streams of airires'pectively through: said heating" p assages andisaidi by -rpassi passage;-; these streams joiningiafter they lavezsaid exit endstoxform a comp'o'sitez'stream'; means for. heating the-: air streams flowing throughsai'd' heating: passages-,: said heating meansincluding avplurality' of temallyspassagedz heating: elements traversing; saidih'eatingfpassages and means foreondizcting: hotiiproducts 'of combustion tothe passages; of: said heating elementsto' -heati said? airstreams' flowing througlit' saidr heating: passages: by' heat conduotion'ithroughi samheating elements; and dampenmeans for controlling the relative; volums off'said-twolair streamsniovingithroughlsaid' heating: passages and theair-stream moving through said byepass passagevandzfor limitingthe: volume 'of said two: airstreams to prevent cooling of said hot products" of? combustion tosuch. extent: as to allow: water tocondense irom' said: products:

in said passaged heating units, said damper means including a=movable shaft iexten'dingacross said heating passages'and: said; by-pass passage;v

twoprimary dam-per members secured to: said shaft in substantially the same angul'arireiationship-to be substantially parallel to each other and respeetivel'y disposed in the air streams which flow through saidh'eating passages, and. an auxiliarydamper'member disposed in the air stream; which flows through said by-pass passage and secured to said shaft to lie at an angle to said" primary: damper members whereby turning} of" said shaft in one direction will simultaneously moveisaid' two primary damper members toward i closed" position'andsaid auxiliary damper membehto'ward open position andmoving said shaft in fanopposite direction will simultaneously move said'two primary damper members toward open position and, said auxiliary. damper member I toward'closed position to dependently adjust the volumeof air flowing through said by -pass pas.- sage relative tothe volume'of. air flowing through said heating passages,

g 2.; Ina heatingunit-for heatingiair by indireet heat transfer with hot product of. combustion while preventingecorrosiont and 1 scaling of the heat tnansfer surfaces by preventing cooling of: the hot"; products of combustion below the dew. point, the combinationof: walls defining aheat ing passage a nda by-passpas'sage disposed side-- bi -side and having entrance ends opening? on: arr entrance chamber; at least one 1 internall'y pasisaged' heating elementtraversing. said heating passage; means for delivering hot products of combustion to the passage of said heating elemerit-7' means for delivering a stream of'air to said entrance chamber to divide between said i heating and 'by pass passages and form separate air streains flowing therealong; and'means'for differentially ehanging the volumes of said air streams, meanscomprising a shaft providing a longitudinal axis extending across said passages and} two dam er memlders seouredto said shaft point,a-the;combination of-:;. walls defining; a hea 8; t'oo'lierat aii'g'leii'relativeito EaUkIiQflTGHHTQMGB speotivelm disposed:- insaid air'streamsz'whereby; tunning? saidshaft: in onezdineoti'on will move one; of said damper members towardiclosedl positiom andthe other dam-per member, towardvopenipo sition: and turning said-n shaft in'ltanzoppositer d motion will move said gone of said dampen-meme; bers toward T open position: ands-aid other :damper i member-toward closed positions 4 -w';

3: In; a: heating unit" for heating ainby l-iidilfiifitfi heat transfer with hotlproduots of -oombustioir while-preventing corrosion and sealing: of the heat-transfer surfacesb preventing-oooling ot the -hot' products of eombustionbelow the, deW;;,

ing passage and a by-pass passageldispasedsid by-side and having entrance ends I opening pn entrance chamberyfatleast; one internally pas l-r saged heating: element traversing .said' heating passage; means fon delivering: hot produots of) combustion to: thepassage, of said 1 hEHJilIlg QIQ ment; means for delivering a streamofiairtqgsaid ,1 entranoeachamber to-divide betweemsaid passages a, and form separate air streams iiowing'thereg;

; along; and means for differentially. ehanginglthe volumes ofsaid air streams this(meanseompris inga plurality of parallel, shafts. extending across said passages,..a firstdamper I nemti'eiis'e.- ..v cured to each shaft and being ,d'ispo'se'd inQonej of i said air strea-r ns,a secondidamper member. sea l cured-to eachshaft and being, disposeddn r other air stream,i the damper member one shaft' .being disposed. in planes substantially; at rightangles to,each. other and eonnefetionl'means rfor simultaneously turning said shafts throu lj l equal angleswhile maintain'ing.said fiizstldamper members inrsubstantiallyi 'parallelplanes' h 4; A heating unit as definedin elai.

whichs-aidtwo damper members extendroutward stantiallyatrightanglesetoleach-other 5. In a heatingunit,thecombinationoflzhwalls defining i a heating passage and a by-pass; passage disposed.- side-by-side' ands having: entranoe': ends adapted' to facea: stream of-airwhereby" portions ofithe: air-flow throughieachw passageway damper means I for dependently controlling; thel; volumes: of? airmoving: through" s-ari'dipassages, said' damper. means: including-"a shaft-extendingacross said passages" and two damper members? secured'to said'sha'ft in different angular -rela'-'--' tionships'and resp'ectiveiy disposed in the air streams moving through said passages; whereby turning saidi shaftine'one direction will move one ofisaid damper members t'oward closed passes and tl'ie other damper member toward' 'opeirplositiong' f a'j heating "element traversing said heatin passage and"pr'ovidi ngan uprightpassag burner for supplying products ofoinbu the lower end 'ofsaid upright passage, said pro 1 1 nets of combustion heating the streamer airn iov ing through said heating passage and bei cooled by this air; and means'forpreventingeoo ing of said productsof oombustion below Qthed point, said last named means including mean responsive to the temperature of the products of combustion" leaving said upright) passage and meansforconnecting same to saiddamper means} to vary .the relatives. volumes of air movingf through said heating passage and" said;,by 1. passage. 7 i 1 fromthe axis. of saidishaft andilie in planes sub g q file of this patent:

Number 10 Name Date Summers Feb. 11, 1930 Summers Feb. 25, 1930 Keenan June 20, 1933 Jaden Jan. 30, 1934 Bell May 8, 1934 Norris Oct. 1, 1935 Beam -Feb. 13, 1940

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US843909 *Jun 8, 1903Feb 12, 1907Frank M PetersAtmosphere-regulating system.
US1734962 *Mar 11, 1924Nov 12, 1929Lucille V ClarkeAir heater
US1737189 *Nov 11, 1924Nov 26, 1929Eugen HaberHeat exchanger
US1746564 *Dec 5, 1927Feb 11, 1930Leader Iron WorksHeat economizer
US1748091 *Dec 12, 1927Feb 25, 1930Leader Iron WorksDetachable head economizer for hot-water and steam boilers
US1914604 *Mar 24, 1931Jun 20, 1933Foster Wheeler CorpAir preheater
US1945223 *Oct 20, 1930Jan 30, 1934Jaden Fred IBlower for hot air furnaces
US1958331 *Mar 14, 1932May 8, 1934F O SchoedingerGas fired unit heater
US2015960 *Mar 26, 1934Oct 1, 1935Lennox Furnace CompanyFurnace construction and control means therefor
US2190349 *Jan 5, 1937Feb 13, 1940Bryant Heater CoHeater
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2713459 *Sep 22, 1951Jul 19, 1955Ray G PhillipsFluid heater control apparatus
US2729433 *Jan 7, 1952Jan 3, 1956Smith Corp A OHeat exchanger with removable tube banks
US2938714 *Oct 17, 1958May 31, 1960Wolverine Equipment CoHooded exhaust system
US2947522 *May 12, 1955Aug 2, 1960Keller John DonaldRecuperators
US2963083 *Mar 23, 1956Dec 6, 1960Modine Mfg CoGas burner structure
US3227208 *Apr 26, 1962Jan 4, 1966Garrett CorpThermally stabilized environmental system
US3443588 *Oct 24, 1965May 13, 1969Aero Flow Dynamics IncDamper means in air supply units or the like
US3841395 *Jan 15, 1973Oct 15, 1974Bosch Gmbh RobertTemperature control for vehicle passenger space
US3889653 *Mar 4, 1974Jun 17, 1975Scogin Clifford AWood burning heater
US3916869 *Feb 15, 1974Nov 4, 1975Inst Gas TechnologyHeat exchange apparatus
US4034803 *Jul 24, 1975Jul 12, 1977John Zink CompanyCorrosion resistant tubular air preheater
US4277453 *Jun 4, 1979Jul 7, 1981United States Steel CorporationWaste gas purification reactor and method
US4371027 *Aug 8, 1977Feb 1, 1983Jacobsen Orval EEconomizer with an integral gas bypass
US4381850 *Oct 16, 1981May 3, 1983Grant Willie TAutomatic air register damper
US4485965 *May 9, 1983Dec 4, 1984Mcginnis George PDual-rate fuel flow control system for space heater
US4498524 *Sep 30, 1982Feb 12, 1985Jacobsen Orval EHeat exchanger with by-pass
US4602610 *Jan 30, 1981Jul 29, 1986Mcginnis George PDual-rate fuel flow control system for space heater
US4926840 *Sep 28, 1989May 22, 1990Rheem Manufacturing CompanyPilot gas bypass system for fuel-fired furnaces
US4974579 *Sep 28, 1989Dec 4, 1990Rheem Manufacturing CompanyInduced draft, fuel-fired furnace apparatus having an improved, high efficiency heat exchanger
US5042453 *Jul 27, 1990Aug 27, 1991Rheem Manufacturing CompanyCompact, high efficiency heat exchanger for a fuel-fired forced air heating furnace
US5293860 *Sep 4, 1992Mar 15, 1994Inter-City Products Corporation (Usa)Standing pilot furnace with vented vestibule
US8789766 *Mar 3, 2008Jul 29, 2014Liebherr-Aerospace Lindenberg GmbhMixing device for aircraft air conditioning system
US20110303135 *Dec 15, 2011Alstom Technology LtdRegenerative air preheater design to reduce cold end fouling
USRE37128 *Oct 3, 1997Apr 10, 2001International Comfort Products Corporation (Usa)Standing pilot furnace with vented vestibule
U.S. Classification126/110.00R, 63/32, 165/103, 165/921, 236/13, 236/11, 110/304, 165/296, 165/101
International ClassificationF24H9/20
Cooperative ClassificationF24H9/2085, Y10S165/921
European ClassificationF24H9/20B3