US2502345A

US2502345A - Heater

Info

Publication number: US2502345A
Application number: US622429A
Authority: US
Inventors: Frank A Ryder
Original assignee: Stewart Warner Corp
Current assignee: Stewart Warner Corp
Priority date: 1945-10-15
Filing date: 1945-10-15
Publication date: 1950-03-28
Anticipated expiration: 1967-03-28

Description

March 28, 1950 F. A. RYDER 2,502,345

HEATER Filed Oct. 15, 1945 3 Sheets-Sheet 2 March 28, 1950 F. A. RYDER HEATER Filed Oct. l5, 1945 3 Sheets-Sheet 3 007' DUR 77725911105 7A T Patented Mar. 28, 195() UNITED STATES PATENT OFFICE HEATER Frank A. Ryder, Chicago, lll., assigner to Stewart- Warner Corporation, Chicago, lll., a corporation of Virginia 3 Claims.

l The presentvinvention relates to heaters and vmore particularly to heaters of the self-contained floor furnace or space heater type. Although the heater shown is intended to be red by fuel gas, it will be appreciated that the major portion of the invention at least is equally applicable to heatersvof the oil fired or even solid fuelY types.

It is an object of the present invention to provide `a small self-contained floor furnace type heater which is economical to manufacture, and which may be easily installed.

A further object of the invention is to lprovide a novel heater of the above type which may be installed in either new or old houses with the minimum of installation difliculty, and with a maximum flexibility of choice of location.

Yet another object of the above invention is to provide a novel heater and control system which has the combustion side entirely sealed from the Ventilating side and in which no chimney is required.

Still another object of the present invention is to provide an improved heater of the above type with means for obtaining better and more even temperature distribution of the heated air than has heretofore been considered feasible in heaters of the oor furnace or space heater type.

Yet another object of the present invention is to provide a novel automatic heater control system.

Another object is to provide a novel heater which maintains a more even temperature in the space to be heated than can be accomplished by simple on-and-off thermostatic control means,

Other. objects and advantages will become apparent from the following description of a pref erred embodiment of my invention in which similar characters of reference indicate similar parts throughout the several views.

In the drawings:

Fig. 1 is a vertical medial sectional view through a floor furnace embodying the present invention, illustrating the major components of the heater and the construction thereof;

Fig. 2 is a medial sectional view of a portion of the control mechanism illustrated in elevation in Fig. l;

Fig. 3 is a horizontal sectional view taken in the direction indicated by the arrows along the line 3-3 of Fig. 2. Fig. 3 may also be considered as a horizontal sectional view looking downwardly as indicated by the arrows along the line 3a-3a ofFig.2;

Fig. 4 is a horizontal sectional v iew looking up- 5s 2 wardly as indicated by the arrows along the line 4-4 o1' Fig. 1. This view indicates the construction of the heat exchanger and the orientation of the burner relative thereto; and

Fig. 5 is an electrical circuit diagram of the control system for the heater shown.

'I'he heater illustrated, which comprises a preferred embodiment o1' the present invention, has a generally cylindrical outer shell Ill secured at its top to a flanged grill l2 adapted to be supported by the flange from the oor Il of the room in which the heater is located. To accommodate the heater, a circular hole is cut in the door and in order to simplify the problem oi.' installation, the dimensions of the heater are such that it will t between standard joist spacing. Thus it is not necessary to cut into the structural elements of the floor in order to locate the heater and therefore no special bracing of the floor is neces- Sary.

The exhaust from the heater is carried outwardly through the side wall of the building through a small diameter tube I6, which may be enclosed within a coaxial tube I8 which also passes through the wall of the building. The space between the tubes serves to convey air for combustion from the outside of the building to the heater through a U-shaped branch pipe 20. To make the connection between the pipe 20 and the tube I8, the inward end of the tube is tted with a collar 22 sealed to the pipe IB and a branch spud 24 is secured to the pipe i8 and surrounds a generally circular opening 26 in the tube. The connection is completed by securing the pipe 20 to the spud 24 preferably at the time of installation.

The heat exchanger portion of the heater comprises a vertically extending sheet 21 which is bent to deep U-form to comprise an inner chamber 28, the upper portions then being rolled over at 30 and bent downwardly generally parallel to the first portion of the sheet as at 32,l and into a position opposite the center of the sheet. At this point the two ends are welded together at 34. In order to stillen the structure, flanged U- shaped spacers 36 are welded to the outer surface of the inner portion of the sheet, that is, the portion of the sheet bounding the chamber 28 and have their opposite ends abutting the outer portion of the sheet. The portion of the structure just described is located within an oval shaped casing 38 comprised of two halves seam welded together at (il along the medial line of the structure. The shell 3B is in turn enclosed within an oval outer shel142 constructed generally similar to the shell 38 excepting that it is sumciently larger to provide an annular space between the shells 38 and 42. The spacing between the shells is maintained uniform by a plurality of spacer elements 44 similar to the elements 36.

The two ends of the portion of the heat exchanger just described are closed by upper and lower header plates 46 and 48 respectively which enclose a gas passage from the chamber 28 around through the annular space between the shells 32 and 38, the lower portion of this latter space being connected to an exhaust tube 50 which is welded to the center of the sheet 38 in a position opposite the seam 34. The header plates have slots therein which register with the slots in the heat exchanger in which are located the

spacers

36 and 44. The 'construction therefore permits Ventilating air to be passed lengthwise through the heat exchanger between the casing 42 and the shell 88 and through the U-shaped slot between the upwardly and downwardly extending gas passages- 28 and 52, respectively. y

The lower end of the heat exchanger is connected to receive Ventilating air from a formed sheet metal plenum chamber l54 adapted to receive Ventilating air from a blower, as will be presently described. This plenum chamber is in communication with the Ventilating air passages previously described so that air passes into the heat exchanger at the bottom and out at the top.

The burner comprises a generally cylindrical tube 56 somewhat longer than the heat exchanger which has a plurality of outlet jets 58 arranged along one side, the total length occupied by the jets being something less than the overall length of the heat exchanger. The tube 66 is closed at its upper end and is provided with a bell mouth 60 at its lower end. This tube extends vertically within the heat exchanger in a position closely adjacent the central portion of the sheet 21 with the jets pointed toward the mouth 62 of the chamber '28, that is, at the point at which the sheet 28 is rolled over as at 30.

The bell portion 80 of the tube 56 is enclosed within a combustion air plenum chamber 64 formed by a flanged cup 66 which is sealed as by welding to the lower header plate 48. This cup has an opening 88 considerably larger than the tube 56 through which the lower portion of the tube extends. The combustion air plenum chamber 64 therefore delivers air both through the opening 68 into a position around the jets 58, and also to the bell mouthed opening 80 of the tube 56.

Gaseous fuel is brought into the heater through a pipe 10, through a gas pressure control valve, indicated generally by the numeral 12` and from the valve through a magnetic shut off valve 13 and pipe 14 to a nozzle 18 having its open end position within the bell 60 so that gas owing from the nozzle 16 will inspirate air to provide a rich mixture of air and gas which burns after it leaves the jets 58, because of the presence of secondary air introduced through the opening 68. Ignition is accomplished by means of a spark plug 18 secured in a bushing 80 welded to the upper header plate 48 in a position adjacent -the uppermost of the gas outlet jets 58. Convenient support for the burner tube l56 is provided by welding the upper end of this tube to the upper header plate 48 and by securing the lower end to the wall of the combustion air plenum chamber 66 by a bracket 82.

The cylindrical casing I0 is divided vertically by a partition 84 so as to provide space on one side for the heat exchanger and burner just described and to provide a second space 88 on the other side which receives inlet Ventilating air and contains blowers and miscellaneous control elements. In the lower portion of the chamber 86 in a position generally below the burner and heat exchanger, a vertical shaft 88 is journaled to rotate in bearings 90 and 92. The upper of these bearings is supported upon a spider 94, the arms of which are secured to a blower housing 86. This blower housing is arranged with an air inlet opening beneath the spider and this opening leads to the inlet of a sirocco type wheel 88 arranged within the usual scroll shaped case |00. The outlet of this scroll shaped case |00 leads to a flange |02 having an opening in register with the same opening at the side of the plenum chamber 54. When the shaft 88 is rotating, air is drawn inwardly through the portion of the grill I2 above the space 86 and passes downwardly into the sirocco wheel 88 and into the plenum chamber 56. From here the air passes upwardly through the passages in the heat exchanger into the space between the heat exchanger and the grill I2. From this chamber the air passes outwardly through the grill to the space to be heated.

Directly beneath the scroll case 96 and formed integrally therewith is a second scroll case i813 having its air inlet |06 at the lower surface thereof. The inlet opening |06 is connected to an elbow |08 which passes through the side of the case I0 and is connected by means of matching flanges ||0 with the combustion air inlet pipe 20.

The outlet of the scroll case |04 is secured by means of a pair of matched flanges H2? to a Venturi section ||4 which in turn leads to an elbow ||8 connected to the combustion air plenum chamber 64.

With the above arrangement it is apparent that whenever the sirocco wheel 98 is operating, the combustion air blower wheel ||1 secured to the lower end of shaft 88 will also be rotating and will draw air inwardly through the annular space between the tubes I8 and I6, through the pipes 20 and |08, and will pass this air outwardly through the Venturi section ||4 and elbow 6 to the combustion air plenum chamber 84. From here a portion of the air is aspirated by the gas nozzle 18 so as to form a rich mixture which passes inwardly through the burner tube 58 and out into the combustion chamber by Way of the nozzles 58. Another portion of the combustion air passes from the plenum chamber through the opening 88 and mixes in the heat exchanger with the rich mixture issuing from the jets. This mixture is ignited by the spark plug 18 and the hot products of combustion pass out through the mouth 82 of the inner chamber 28, around through the side passages, and outwardly through the exhaust fitting 50 to the exhaust pipe |6 to which the latter is connected by a pair of mating flanges H8. From the exhaust pipe |6 the products of combustion pass outwardly to the air through the wall oi' the building.

The blower shaft 88 is driven by an electric motor |20, the power transmission being by way of pulleys |22 and |24 and belt |26.

In order to make the unit extremely easy to install, it will be noticed that the flange ||8 at the end of the exhaust pipe 50 and the flange Hl at the end oi' the elbow |08 arey recessed in de-` pressions |28 and |30,'respectively, in the side wall of the case |0 so that the entire heater can be lowered through the opening in the iloor I4 without the necessity for cutting special openings to clear these flanges. Similarlythe motorand its bracket |32 can be attached to the heater and the belt |26 located upon the pulleys after the heater has been lowered into place. Actually the motor is shown in the position illustrated merely for clarity of illustration. It is preferred that this motor be located inside the space ,86 at approximately right angles to the position shown so that the entire mechanism can be located within a single housing prior to installation.

The control system for the present heater comprises a simple relatively low cost arrangement such that the heater can be fully on at a high heat position while the'space is being heated from an originally low temperature or whenever such a large amount of heat is needed. After the temperature reaches approximately 68, the heater is automatically cut down to a low heat range where it stays unless either the room cools down suillciently to require full heat, or unless the temperature in the room continues to rise, in which latter event the heater is shut ofi at about 70. The heat output at the low heat position is not constant but depends upon the temperature of the outside air so that whenever the ambient temperature is low, the heat produced in the low heat position is automatically higher than the amount of heat produced in the same position under more temperate conditions.

'I'he heater also includes mechanism for shutting oil.' the ow of fuel if combustion does not start within approximately 45 seconds, and for preventing further operation of the heater until this control has been manually re-set. In addition, if the room temperature rises above 70, the heater will not return to operation until the temperature has dropped below the low heat range and thus, the heater always starts in the high heat position.

All of the above is accomplished by relatively simple means shown in physical outline in Fig. 1. The construction of the gas regulator is shown in greater detail in Fig. 2, while Fig. 4 illustrates the electrical circuit. The wiring in Fig. 1 has been deleted in the interest of clarity of illustration.

The gas pressure regulatory illustrated in Figs. 2 and 3 comprises a lower chamber |34 formed in a casting |36 w'ith a threaded opening |38 to receive the inlet gas pipe 10. This chamber is separated from an upper chamber |40 by a partition |42, which has a centrally located vertical threaded opening |44 therethrough into which is tted a valve seat |46. This valve is closed on its lower side by a poppet type valve |48' so that whenever the valve is depressed,.gas can pass from the chamber |34 around the valve |48 through the valve seat bushing |46 into the chamber |40 and thence to a gas outlet'pipe 14 communicating with the upper chamber |40.

The upper face of the casting |36 is flat and matches the lower face of an intermediate casting |50. The inner wall of the lower casting |36 at the upper end is so shaped that the chamber |40 at this point forms a circular opening which matches a similar opening in the casting |50. These two castings are secured together by means of screws |52 and clamped between them is a soft flexible gas impervious diaphragm |54 which forms the upper closure of the space |40. The

The diaphragms |62, |54 and the poppet valve |48 are all secured to an axially movable valve stem |66 which extends centrally through the device and is secured at each end to a soft acting spring |68 which together serve both to urge the valve stem 66 in an upwardly direction `with very light pressure, and also to position the valve stem axially of the device and resist radial movement.

As shown in Fig. 3, each of these springs consists of a disc of very thin sheet metal having openings |10 cut therethrough so as to leave a hub |12 at the center for attachment to the stem |66 and narrow arms |14 spiraling outwardly to theperipheral portion of the disc. The springs |68 are clamped against the ends of the castings 38 and |60 by dish shaped covers |15 and gaskets |11, secured by screws |19. Each of the diaphragms |54 and |62 is stiffened at the central portion by plates |16 which restrict exure of the diaphragm to the peripheral portion between the plates and the cast housing.

The intermediate chamber |56 is connected by means of a threaded opening Ij'lilA in the casting |50 to a fitting |80 leading to a tube |82 which in turn is connected by a iltting |84 to the throat of the venturi I4. Similarly the upper chamber |58 is connected by way of a threaded opening |86, fitting |88, and tube |90 to a fitting |92, which extends through the side wall of the elbow ||6 in a position slightly downstream of the venturi and is curved so as to form a ram |94 facing into the stream of flowing air.

The operation of this portion of the device is as follows: Whenever the speed of the blower is "increased, a greater quantity of air is forced through into the combustion air plenum chamber 64 and thence to the burner. This greater quantity of air requires more fuel in order to maintain a proper fuel-air ratio and this increase in fuel flow is provided by the gas pressure regulator 12 in the following manner. As the flow rate through the venturi ||4 increases, the pressure at the iltting |84 will be decreased while the pressure at the small ram |94 will increase. Since these two fittings are communicated to the pressure regulator by way of pipes |82 and |90, respectively, the result is that the pressure in the intermediate chamber |56 is decreased, while the pressure in the upper chamber |58 is increased. This increase in pressure differential across the diaphragm |62 causes the diaphragm to tend to urge the valve stem |66 downwardly, thus opening the l poppet valve |48. The gas flow from the pipe 10 to the pipe 14 is therefore at a greater rate and the gas pressure in the chamber |40 will rise until the gas pressure againstthe lower surface of the diaphragm |54 is suflicient to return the valve to equilibrium. In other words, any increase in the pressure differential across the upper diaphragm will be accompanied by a higher gas pressure and `the gas pressure will rise until the force of the gas pressure acting upwardly on the lower diaphragm |54 equals the forces produced by the difference in air pressure acting upon the upper diaphragm |62 and the lower diaphragm 54.

It will be noted that the low pressure in the intermediate space |56 operates on both the diaphragms |54 and |62, but since the upper of these dlaphragms has greater area, the net effect is to produce a force equal to thepressure operating against a diaphragm having an area equal to the area of the larger diaphragm minus the area of the smaller.

It is apparent, therefore, that the heat output of the heater can be increased by increasing the voltage drop across the electric motor |20 since this will cause a higher blower speed both of the combustion air blower and the Ventilating air blower. As it has been explained previously, an increase in the speed of the combustion air blower causes a greater ow of both air and gas to the heater and, therefore, a higher heat output rate. At the same time the increased speed of the ventilating air blower 98 supplies a larger quantity of Ventilating air to carry away the additional heat.

The electrical system, which is intended for operating on an alternating current circuit, comprises a step-down control transformer 200 connected by way of a plug and cord 202 to an outlet box 204 or other source of electrical energy. One side of the high voltage side of the line is connected by way of a lead 206 to a normally open contact 208 in a relay 2 I0. The cooperating contact 2|2 is connected by way of the line 2|4 through a normally closed over-heat limit switch 2|6 to a latch open type safety switch 2I8. The over-heat limit switch may be of the conventional bimetal type and is located in the space above the upper header plate 46 in such manner that if for any reason Ventilating air becomes shut off, such as by someone placing newspaper, a pillow or some such object over the grill |2, the increase in temperature of the bimetal element will cause the electric current to be interrupted.

The latch open type safety switch may be arranged with one contact secured to a bimetal strip in such manner that heating of the strip causes the contacts to separate. This bimetal strip is in turn provided with an electrical heating element 2 I 1 which can receive current for a short interval at starting in a manner to be explained presently. The switch is so timed that approximately 45 seconds of heating is required before the contacts separate. As a further safety precaution the switch is so arranged that once it has opened, it latches in the open position and will not return to circuit closing position until manually re-set.

The latch open type switch 2|1 is connected in turn by way of a lead 220 to the fan motor |20, 58

the opposite terminal of which is connected through a series reactance 222 to the other side of the line indicated in the drawings by the wire 224. The resistance of the motor |20 and reactance 222 together can be altered by means of a variable resistor 226 shunted across the reactance. The resistor slider is mechanically connected to an expansible bellows element 228 which communicates through a tube 230 with a temperature sensitive bulb 232 located in the combustion air inlet duct 20. The connections to the resistor are such that an increase in temperature of the incoming combustion air will cause an expansion of the gas or vapor in the bulb 232 thereby causing an elongation of the bellows 228, and this elongation in turn operates to increase the resistance across the reactance 222 so as to increase the resistance of the system as a whole.

The fuel system magnetic shut-off valve 13 previously referred to is connected between the line 220 and the lead 224 so that this valve is energised at the same time as the motor |20. The heater coil 2|1 in the safety control 2|8 has one of its ends connected to the wire 220, while the other end is connected by way of lead 284 to a terminal 236 of a single throw double pole flame detector '288. 'I'he terminal 236 is also connected to one end of the primary 240 of a step-up spark transformer 242, while the other end of the primary is connected by way of lead 244 to the line 220 between the motor |20 and the safety switch 2 I8.

The iiamedetector 238 is of the type having contacts which are closed when the device is cold and in which the contacts open within about to 80 seconds after combustion starts. As mentioned previously, this detector is oi' the double pole single throw type in which both switches of the double throw combination are opened and closed at the same time. The contact 246 in the device, which operates in conjunction with the contact 288, is connected 'to thi side of the line represented by the lead 22 Of the other set of cooperating contacts in the flame detector, one of these, 248, is connected to a line 250 leading to one end of the coil 252 in the relay 2|0, the other end of this coil being connected to one side 254 of the control transformer 200. 'The other contact 256, which cooperates with the contact 248, is connected by lead 258 which extends to one of the contacts 260 in the room thermostat 262.

The room thermostat is of the double pole single throw type with the temperature differential between the two sets of contacts such that as the temperature rises, the contact 260, previously mentioned, is separated from its cooperating contact 264 at a temperature of approximately '10", while the other two

contacts

266 and 268 are separated upon a rise in temperature to about 68.

The thermostat contact 264 mentioned as cooperating with the contact 260 is connected by lead 210 to the opposite side 212 of the control transformer 200, this side of the transformer also being connected by lead 214 to the contact 266 in the room thermostat. The contact 268 which cooperates with contact 266 is connected in turn V by way of lead 216 to the coil 218 of a normally open relay 280, the opposite end of this coil being connected in turn by way of lead 282 to the side of the control transformer represented by the lead 254. The set of contacts 284 closed when the coil 218 is energized are shunted across the reactance 222 and resistor 226 by way of leads 286 and 288.

As explained, the relay 2 0 is of the double pole single throw type. The set of contacts in this relay not previouslyy mentioned are indicated by 00 the numeral 280 and are bridged across the

leads Y

250 and 258.

One lead of the secondary 292 of the spark transformer 242 is connected to one side of the spark plug 18, while the other sides of the spark plug and transformer secondary are grounded in the usual manner.

The control system above described operates in the following manner: Assume for the moment that the heater has been turned oil, such as by the opening of a switch (not shown) in the main line 202, and that the temperature is below 68, and further that the heater has been ofi' sutilciently long so that the flame detector has cooled.

Under the above conditions, the control system 8l is characterized by the following features. The

contacts 2|2 and 208 in the relay 2|0 are separated, as are the other set of contacts 290, in this same relay. The room thermostat contact points 260and 264 are closed as are the contacts 2'66 and 268. Contacts 284 of the relay 280 are"

open whilethe contacts

236 and 246 and 256 and 248 of the 'flame detector are closed. Similarly, the over-heat ylimit switch 2|6 is closed as are the contacts 2|8Vof the latch open limiting device 2|1.- f ,t v

Under ythese conditions the gas shutoil` valve 13 is deenergized and therefore closed, as are the motor |20`and spark transformer 242 which therefore `are not operating. The variable reslstor 226 may be in any position such that'the resistance is fully in or fully out of the circuit, or somewhere in'lbetween, depending upon the temperature of the voutside ambient air as has been previously indicated. y

If, under the above conditions, the heater circuit is energized, the control transformer 200 will energize the relay 2 0 by way of

line

212, 210,

contacts

264 and 260, line 256,

contacts

256 and 248, and line 260. Energization of the coilr 2| 0 closes the'contacts 208 and 2|2, as wellas the contacts 290. The contacts 290 when closed operate to hold the circuit through the relay coil 2 0 even though the

ame detector contacts

248 and 256 subsequently open. Operation of the relay 2|0 energizes the motor |20 and the gas shut-off valve 13 by way of line 206, contacts 208 and 2|2, line 2|4, over-heat limit switch 2|6, the latch open safety switch 2|8, line 220 and thence through the gas shut-oil valve coil 13 to the return line-224, and also through the heater |20, line 288, contacts 284 (these contacts being closed inasmuch as relay 260 is energized by way of line 212, 214,

contacts

266 and 268, line 216,relay coil 218, and return lines 262 and 254) and thence by way of line 286 to the return side of the line 224. Also the spark transformer 242 will be energized by way of line 224, the primary winding 240, flame detector contacts 236 and 246 to the return line 224. `Energization of the primary. of course, energizes the secondary 282 so as to produce sparking at the plug 16, it being assumed throughout the description that the line 202 is connected to an alternating current circuit.. Further the heaterl coil 2|1 of the latch open safety switch is energized by way of the line 220 and line 234, leading to contact 236 of the flame detector.

The end result is that the ignition is turned on, the blowers are operating, and fuel is being supplied through the gas `control valve 12. Inasmuch as the motor is running at full speed, the gas will be supplied at the maximum rate as has been previously described.

If the heater does not start within 45 seconds or so, the safety switch 2|8 will be suiilciently heated by the coil 2|1 so that it opens the crcuit to the motor |20, gas shut-off valve 13 and spark transformer 242. Once opened, the switch 2|8 will not re-close until manually re-set.

If the heater starts immediately in the normal manner, the flame detector contacts 236 and 246 will be separated as

will contacts

248 and 256 in approximately 15 to 30 seconds. Opening of the

contacts

256 and 248 will deenergize the relay coil 2|0, were it not for the holding contacts 290. Since these holding contacts remain closed, separation of the

contacts

248 and 256 in the flame detector has no immediate effect excepting to condition the circuit for future oper- 236 and 246.deenergizes the heating coil 2|1 withk ation. Separation of the llame detector contacts the result that the safety switch 2|8, which has been heated for a period of from 15 to 30 seconds; now starts cooling and cools back to ambient temperature without the contacts in this switch ever having been separated.

As the temperature in the room rises to approximately 68, the

contacts

268 and 266 will be separated, thereby deenergizing the coil 218 of the relay 280. This permits the contacts 284 to separate, thereby requiring the motor to receive its current through the reactance 222 and the variable resistor 226 in shunt therewitln The amount of resistance 226 in shunt with the reactance depends upon the ambient outside temperature as has been previously described. If the weather is extremely cold, the resistance 226 Will be su-bstantially completely out of the circuit, with the result that the motor |20 operates almost as fast as it does when the contacts 284 are closed. The heat output, therefore, drops ol only slightly. If, on the other hand, the outside air temperature is quite mild, the resistance 226 will be annost completely in the circuit with the result that the resistor 226 and reactance 222 will divide the current to the motor in such manner that the motor operates with much lessL current flow than when the contacts 284 are closed. The

result is that the motor speed is much lower and therefore the heat output rate is much lower. In general, the system should be so balanced that the heater will normally almost but not quite maintain the desired room temperature at any given outside air temperature at the low heat output rate as set by the temperature bulb 232 for that particular temperature.

If the room now commences to cool and the temperature drops below 68, the

contacts

266 and 268 re-close, thereby closing the contacts 284 which in turn speeds up the motor |20, thereby shifting the heating system to the high heat output level.

On the other hand, if the temperature in the room continues to rise after the heater has been shifted to the lower heat output level and the temperature rises above 70 or thereabouts, the

contacts

264 and 260 are separated, thereby de- -energizing the relay coil 2|0, inasmuch as the

flame detector contacts

238 and 256 have already been separated, with the result that the circuit to the motor |20, gas shut-off valve 13 and spark transformer 242 is interrupted by the separation of relay contacts 208 and 2|2.

If the temperature now starts falling and drops below 70, the

contacts

260 and 264 re-close and the heater is restarted at the low heat level, providing enough time has intervened to permit the flame detector to cool sufllciently so that

contacts

248 and 256 have re-closed. If, however, the flame detector has not had an opportunity to reclose, nothing happens until the flame detector has had an opportunity to cool. The flame detector therefore protects the latch open switch 2|8 in that it always gives the latch open switch an opportunity to cool before the start of a new cycle. This is advisable since otherwise it is possible that the heater might have been turned on just long enough to cause the heater 2|1 to bring the latch open switch up almost to opening temperature, at which point if someone moved the thermostat to a lower temperature setting, thereby turning on the heater, and then moved it back-again to a suiciently high temperature setting to cause the heater to come on once more,

it would be possible for the heating element Ill to be reenergized. such that the heat additionally supplied plus the residual heat remaining in the device from the last cycle might be enough to cause this switch to open and latch in the open position, even though there was no abnormal functioning in the heater. This is prevented by the

llame detector contacts

256 and 248 which, under the above recited conditions, would remain open between the cycles long enough to permit the switch 2 I8 to cool nearly to ambient temperature before reenergization of the circuit through the heater coil 2| 1.

If at any time the heater becomes too hot, the over-heat control 2li opens and shuts of! the heater.

While in the above description of a preferred embodiment of v the invention certain specic temperatures and time intervals have been recited. it will be understood that they are used merely by way of illustration and not in a limiting sense, and further it will be apparent to those skilled in the art that substitutions and modifications may be made while still retaining the substance of the invention.

Having thus described my invention, what I claim as new and useful and desire to secure by Letters Patent of the United States is:

1. In a heating system, the combination comprising a combustion air blower, a Ventilating air blower, a variable speed drive means connected to drive both said blowers, heater means, duct means for connecting said combustion air blower to supply combustion air to said heater means, said Ventilating blower being arranged for ventilating said heater means, connections for supplying fuel to said heater means, valve means in said connections for controlling the rate of fuel flow to said heater means in response to the rate of combustion air ow, thermostatic means sensitive to the heated space temperature for cycling said heater means between high heat and lower heat positions, other thermostatic means operative when the heater means is cycled to the lower heat position for varying the speed of said drive means. the last said thermostatic means being sensitive to changes nrambient air temperature, and means operated by the rst thermostat when said iirst thermostat is moved to the high heat position to render said second thermostat ineffective to aiect the combustion air flow rate.

2. In a heating system, the combination comprising means for supplying combustion air at a variable rate, Iheater means, duct means for connecting said heater means tosaid combustion air supplying means, connections for supplying fuel to said heater means, valve means in said connections for controlling the rate of fuel ilow to said heater means in response to the rate of combustion air ilow, thermostatic means sensitive to the heated space temperature for cycling said heater means between high heat and lower heat positions, and other thermostatic means operative when the heater means is cycled to the lower heat position for varying the rate of combustion air now, the last said thermostatic means being sensitive to changes in ambient air temperature, and means operated by the first thermostat when said first thermostat is moved to the high heat position to render said second thermostat ineffective to affect the combustion air ilow rate.

3. In a heating system, a heat exchanger, ventilating air circulating means for withdrawing air from the heated space for passing the air thus withdrawn over said heat exchanger and for returning the air from the heat exchanger to theV heated space, combustion means for heating said heat exchanger, means for supplying combustion air at a variable rate to said combustion means, said combustion air supply means being connected to receive combustion air directly from the outside atmosphere, thermostatic means sensitive to the temperature of the heated space to cycle said combustion means between high heat and lower heat positions, and other thermostatic means operative when the combustion means is cycled to the lower heat position for varying the rate of supply from the combustion air supplying means, the last said thermostatic means being sensitive to changes in ambient air temperature and being located within the combustion air supply connection.

FRANK A. RYDER.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,583,238 Scudder May 4, 1926 1,645,506 McKee Oct. 11, 1927 1,932,269 Harrington Oct. 24, 1933 1,949,735 Bulkeley Mar. 6, 1934 2,038,578 Lamb Apr. 28, 1936 2,211,694 Hartig Aug. 13, 1940 2,224,544 Keller Dec. 10, 1940 2,226,510 Grant Dec. 24, 1940 2,286,853 Holthouse June 16, 1942