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Publication numberUS3452737 A
Publication typeGrant
Publication dateJul 1, 1969
Filing dateJun 9, 1967
Priority dateJun 9, 1967
Publication numberUS 3452737 A, US 3452737A, US-A-3452737, US3452737 A, US3452737A
InventorsPellegrino Joseph Eugene, Seratt Robert H
Original AssigneePellegrino Joseph Eugene, Seratt Robert H
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Fireplace control and heat exchange unit
US 3452737 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

July 1, 1969 J. PELLEGRINO ETAL 3,452,737



FIG. 3.

y 1969 J E. PELLEGRINO ETAL 3,452,737

FIREPLACE CONTROL AND HEAT EXCHANGE UNIT Filed June 9, 1967 Sheet 3 of 2 MM/m7 WW ATTORNEX United States Patent US. Cl. 126121- 6 Claims ABSTRACT OF THE DISCLOSURE A fireplace control and heat exchange unit is provided for placement in a finished, conventional, open fireplace without modification of the fireplace structure. The unit features a combined grate and heat exchanger, consisting only of rigid sets of horizontally disposed hollow grate bars. The bars of each set are connected end to end to form a tortuous course of multiple bar length. Means are provided for effecting a forced flow of air from "the room, through the hollow grate bars, and then back into the room at substantial velocity and in substantial volume, all at or near floor level.

The unit also includes a decorative, sealing frame for the fireplace, together with means separately, adjustably controlling and limiting the admission of room air to the combustion space above and below the grate, for regulating the intensity of the fire.

The unit is light in weight and does not require to be attached to anything, so it can be readily moved out of the way for cleaning of the fireplace and/or chimney, or for servicing of the unit.

This invention relates to fireplace control and heat exchange units, adapted to be removably placed in a finished, open fireplace of conventional design.

It is a primary object of the invention to provide a novel, portable unit, adapted for application to a conventional open fireplace without structural alteration of the fireplace, for withdrawing air from the room, heating it, and returning it to the room at or near the floor level, and which includes a novel heat exchanger of outstanding effectiveness.

It is a salient feature of the invention that the novel heat exchanger consists only of rigid sets of horizontally disposed hollow grate bars, with the bars of each set connected end to end in communicating relation to form a tortuous course of multiple bar length, together with means for effecting a rapid forced flow of air through the grate bars.

It is a further feature that the novel unit includes a frame, supported from the hearth, which seals the fire place opening marginally and which is combined with means for separately controlling the admission of room air to the fireplace space above the grate on the one hand, and below the grate on the other.

Open fireplaces, in general, are notoriously inetficient as space heaters. None of the combustion gases can be allowed to travel out into the room because that would pollute the air which the occupants must breathe, and hence the only normal way of transferring the heat of the fireplace directly into the room is through radiation. Since the intensity of radiated heat is inversely proportional to the square of the distance from the heat source, there is an intensely hot zone immediately adjacent to the fireplace, but there is generally a marked deficiency of heat at only a short distance from it. Most of the heat goes up the chimney with the combustion gases, and some of the warm air from the intensely hot zone is aspirated into the fireplace opening by the convection current of the combustion gases, and goes up the chimney with them. This aspirated air not only causes an important loss of 3,452,737. Patented July 1, 1969 heat, but it acts as an effective check draft, tending to diminish and limit the intensity of the fire.

Ina house which is normally otherwise heated, as by a central furnace, an open fireplace fire is simply a decoratively luxury. The fireplace combustion air, heated by the furnace, and including only twenty percent oxygen in its composition, is withdrawn from the room and, with the oxygen partially consumed by the fire, flows up the chimney, drawing other heated air from the room over the fire and up the chimney with it. The withdrawn air is necessarily replaced by cold air drawn into the building from'outside.

Creditable advances have been made by providing means for separately controlling and limiting the admission of air to the fireplace opening below and above the fire, but with a further diminution in efiiciency of heat transfer to the room. Air admitted below the fire increases the intensity of the fire, while air admitted above the fire functions as a check-draft or dampener. Both functions are important, depending upon whether the room is too cold or too hot.

Coupled with the control means referred to, heat exchangers have, in some instances, been included, generally for extracting heat from the combustion gases, but in rare instances, and then to a slight extent, directly from the burning fuel, itself. These heat exchangers have been inefiicient and inadequate. In some instances, the heat exchanger designed for the extraction of heat from the combustion gases has been built into the masonry structure of the fireplace during the erection thereof. When thus concealed in the fireplace structure, the appearance of the fireplace has been attractive, but the conductivity of the heat exchange medium has been poor, and the amount of heat recovered, and the rate of recovery, leave much to be desired.

Other units, not of the built-in variety, have been provided. These units as a rule, however, have involved the permanent installation of rather elaborate and massive hardware in the fireplace opening, extending from bottom to top thereof, for extracting heat from the combustion gases. They are heavy, expansive, unsightly and generally quite expensive as compared with the modest service performed. They are generally, if not always, fixed in place, so they cannot be moved out of the way for fireplace cleaning.

In some instances, hollow grate bars have been utilized as parts of heat exchangers, in which case the portions of the heat exchanger constituted by the hollow bars have been located very near to, or even, to a slight degree, in direct contact with, the intensely hot, massive, burning fuel--the ideal source of heat, because of its temperature and mass. The importance of this heat source has not been appreciated or effectively exploited, however, for where hollow grate bars have been utilized they have been of small fiow capacity and have been treated merely as auxiliary to the principal heat exchange structure. The room air transmitted has generally been permitted to pass through the bars in short straight parallel runs and has then, still confined, been mixed with other air and transmitted upward with the object of extracting further heat from the combustion gases. The air has then been returned to the room at a considerable elevation. Returned to the room at an elevation, the heating of the air is of no benefit to infants and small children, and it keeps nobodys feet warm. In fact, the returned air quickly rises by convection to a level at or near the ceiling and contributes little to the comfort of anyone.

We have found that by making the grate consist ex clusively of hollow bars of substantial flow capacity, connected rigidity end to end in communicating relation, to define tortuous courses, and by providing for a forced flow of air through the grate bars alone, an inexpensive,

J light, compact, fully portable heat exchanger can be provided which is far more effective than any fireplace heat exchanger heretofore known.

Such a heat exchanger has the additional advantages that it does not clutter the fuel space of the fireplace opening, that it does not disfigure the fireplace with unsightly hardware, that it returns the heated air to the room at or near floor level and at a suflicient velocity to carry it to distant points, and that the unit of which it forms a part can be withdrawn for fireplace cleaning or for inspection and for repairs of the exchanger itself and/ or the fireplace.

The inner surfaces of the hollow grate bars can be seen to be red hot after the fire has been burning for only a short time, so that the transient air is heated rapidly by radiation as well as by conduction. In order to prevent the return of the air to the room at objectionably high temperatures, the air must be passed quickly through the exchanger. It is partly for this reason that the air is discharged at a sufficient velocity to set up air currents which travel completely across the room and even into adjacent rooms.

The drawing forming part of this specification includes five figures.

FIGURE 1 is a front isometric view of a practical and advantageous control and heat exchange unit illustrative of the invention and embodying features thereof;

FIGURE 2 is a view in sectional side elevation of the unit of FIGURE 1, in association with a fireplace, taken on the staggered section line 2--2 of FIGURE 3, looking in the direction of the arrows, no section hatching having been applied, however;

FIGURE 3 is a horizontal sectional view of the unit and fireplace, the section being taken on the line 33 of FIGURE 2, looking in the direction of the arrows. Again the section hatching is omitted;

FIGURE 4 is an end view in elevation of the damper structure of the novel control and heat exchange unit, provided for adjusting the draft above and below the grate level; and

FIGURE 5 is a detail view in front elevation of the rear wall of a box-like structure which forms part of the unit of FIGURES 1 to 3.

The illustrative unit is shown removably applied to a conventional masonry fireplace 12, having a hearth 14, a face 16, a fire recess or opening 18, a flue or chimney and a conventional damper 22. The fireplace opening is generally of a shape like that indicated in FIGURES 2 and 3. The floor portion 24 of the fireplace opening is, as usual, disposed below the level of the hearth, to provide a slight down-draft for air entering the fireplace, and to confine ashes and burning embers within the bounds of the fireplace opening.

The unit 10 is a generally rigid structure which includes a lower box-like portion 26 that rests on the hearth, and a comparatively thin upright fireplace framing, sealing, and decorative portion 28.

The upright portion 28 includes rigid metallic upright members 32, and rigid metallic horizontal members 34 and 36, the horizontal and vertical members being suitably united as by welding. The width of the unit exceeds the width of the fireplace opening, the unit desirably extending about six inches beyond the opening at either side. The height of the unit exceeds the height of the fireplace opening by a few inches.

The members 32 and 34 are formed with rearwardly extending marginal flanges. It is through the flanges that the parts are joined to one another and to the top wall of the box-like structure 26. The rearwardly extending marginal flanges bear continuously against face portions of the fireplace adjacent the sides and top of the fireplace opening, forming what are, for practical purposes, sealed joints. Packing may be inserted within the flanges to improve the seal, but this seems to be an unnecessary refinement. Within the frame formed by the members 32,

34 and 36 a pair of glass doors 40 are mounted by means of hinges 42, with capacity for swinging about vertical axes. The doors include frames 44, heat resistant, transparent panes 46, and pull knobs 48. When closed, the doors substantially meet along the vertical median line of the frame and seal the fireplace opening against admission of air thereto through the doorway. The doors can be kept closed, or they can be opened as desired for check draft regulating purposes. The doors can be opened wide to provide an unobstructed opening for fuel replenishment purposes.

The box-like structure 26 is composed chiefly of front and rear walls 50 and 52, and top and bottom walls 54 and 56. All four of these walls extend the full width of the unit, but the front and rear walls have openings, as will be pointed out, for purposes which will be made clear as the description proceeds. The box-like structure 26 is open at its ends for the intake of air. In the end portions of such structure which lie outside the lateral bounds of the fireplace opening, are mounted fans 58 of the peripheral blade type, the fans being driven about fore-and-aft extending, horizontal axes, by electric motors 60, desirably of the squirrel cage induction type. The lefthand fan 58 is driven counterclockwise, and the righthand fan is driven clockwise, both as viewed from the front of the unit. Each fan draws in air through the associated open end of the box 26 and delivers the air through an associated, rearwardly opening, duct or chamber 62.

Circular openings 64 are provided in the rear wall 52 of the box 26 to provide outlets for the chambers 62. There are provided as unitary parts of the fireplace unit chosen for illustration herein, two grate bar sets 66, these sets, as shown, being mirror images of one another. Each grate bar set 66 is composed of hollow steel pipe sections or bars 68, 70, 72 and 74, which are cut on bevels as shown and are rigidly connected to one another, as by welding, in end to end, communicating rela tion to form a tortuous course, having a succession of sharp turns, and of multiple bar length. The pipe used is desirably of two and one-half inch internal diameter and has walls one-quarter inch thick. Each bar 68 is a rearwardly extending intake bar. A bar 68 has its open, intake end disposed to form a closed connection with the box wall 52 around the opening 64, being continuously welded to said wall. Each bar 74 is a forwardly extending discharge bar, having its forward end disposed to fit within and to pass through an opening 76 of the box wall 52. The bar 74 is continued forward to discharge air through an aligned opening 78 of the front box wall 50. Each bar 74 is continuously welded to the walls 52 and 50 around the openings 76 and 78. The bar 74 terminates substantially flush with the wall 50.

Between each chamber 62 and the adjacent bar 74 the wall 50 is formed with three horizontally aligned rows of draft openings 80. In back of each of these rows, the wall 52 is provided with a large, arched opening 81 for transmitting admitted air to the fireplace opening. Details of the draft regulating means are illustrated in FIGURE 4. The holes of a row are spaced from one another somewhat farther than the length of the diameter of a hole, with some extra spacing in the middle of the row. Behind each row of holes there is provided a slide bar 82, mounted between parallel channel forming guides 84 which are welded to the back of the wall 50. Each slide bar 82 is provided with holes corresponding in number, size and spacing with the holes 80 of the associated row.

Each slide bar 82 is provided midway of its length with an operating finger piece 86, having a threaded screw stem 88. A spacer sleeve or washer of slightly greater thickness than the wall 50 surrounds the stern and fills the width of a horizontal slot 92 which is formed in the wall 50. A nut 94, threaded on each stem, clamps the slide 82, the spacer 90 and the finger piece 86 firmly together.

Diamond mesh screen panels 96 are desirably provided for the ends of the box 26, and the central front portion of the wall 50 through which the grate bars 74 discharge. These diamond mesh panels are both decorative and useful, since they serve to mask the motors and fans which force air through the grate bars, and the open discharge ends of the bars 74. They serve also to protect the intake and discharge ends of the grate-bar-heat-exchanger combination against the admission of extraneous objects. Other, purely decorative diamond mesh panels 98, matching the panels 96 in appearance, cover the end portions of the framing 28, and top and front portions of the box structure 26 as shown.

It is usual for fireplaces to be constructed with the floor or bottom of the fireplace opening located below hearth level, as previously noted. The depths of such depressions vary from fireplace to fireplace. Provision is made, therefore, of adjustable supporting means for the grate, so that the grate support may be consistent with the support for the box 26 afforded by the hearth, and with the vertical disposition of the framing and sealing portion of the unit. The two sections of the grate are rigidly connected at their rear extremities by a connecting pipe or bar 100 which is welded to the grate sections at two rear corners of each of them. The air discharge bars 74 are additionally rigidly connected to one another, by a connecting pipe or bar 102. The pipes 100 and 102, respectively, have holes 104 and 106 formed through them, and nuts 108 are welded to the under surfaces of the pipes in line with the holes. Headed bolts 110 are threaded upward through the nuts 108 and pass freely through the holes in the connecting pipes or bars 100 and 102. The bolts may be turned individually to effect heightwise adjustment of the grate bar portions to which they are connected, so that the grate will be solidly supported in a horizontal attitude and at a height consistent with the level at which the box 26 is supported on the hearth.

A thermostat 110 of conventional design may be provided for shutting off the fan motors at a preset maximum temperature, and for setting the motors into operation at a preset minimum temperature. A single thermostat controls both motors.

It will be seen that the control and heat exchange unit leaves the part of the fireplace opening above the grate clear and uncluttered. The unit does not require to be built in, or to have any special preparation made for its reception. The unit does not require to be attached to anything. Since the unit weighs only about forty pounds, it can be readily withdrawn from the fireplace and moved out of the way when the fireplace requires cleaning.

All fireplace heat exchangers are subject to erosion and eventually have to be renovated or replaced. This can be most economically taken care of in a light, portable, freely removable unit.

The motor driven fans and the grate bar heat exchanger combine to form a heat exchange unit of unparalleled effectiveness and efficiency. The intensity of the heat, and the availability of it at the fuel or ember level is indicated by the fact that the grate bars soon become red hot on their inner surfaces. Since the inner surfaces of the grate bars are normally at or near red heat, it is important to put the air through them in sufiicient volume and at a sufiiciently rapid rate to avoid an objectionably high temperature of the air returned to the room, while providing a high rate of heat transfer.

The grate bar dimensions, the fan capacities and other factors could be varied widely. The details of the structure chosen for illustration are, nevertheless, informative and of interest. Since the grate bars have internal diameters of two and one-half inches, each has a fiow area of about five square inches, and the two grate bar sets have a combined flow area of about ten square inches. The fans have a combined capacity of 155 cubic feet per minute. The air, therefore, travels through the grate bars and is discharged to the room at a velocity of approximately twenty-four miles per hour. As it emerges it picks up room air and loses velocity very quickly. The air, nevertheless, persists in its travel at reduced speed to distant parts of a large room, and even into communicating adjoining rooms.

Some of the reasons why the grate bars form such an outstandingly efficient and effective heat exchanger are as follows:

1) The grate bars lie continuously in contact with, or in close proximity to, the fuel, including the glowing embers. They are heated chiefly by the fuel which they support and contact, and by embers which have fallen in chuncks through the grate bars and accumulated on the floor of the fireplace opening. They intercept the radiant heat very near its source.

(2) The outer surface of the fuel, at least, must be at or above the kindling temperature of the fuel.

(3) The hot fuel is of high density and mass as compared with the combustion gases and has high specific heat. A great quantity of heat is stored in it and made available by it.

(4) The metallic pipe walls are of limited thickness, and have a high coefficient of heat conductivity.

(5 Because the transient air is mixed thoroughly Within the grate bars, by the frequent sharp turns of the grate bars, it is impartially exposed to contact with the hot walls of the grate bars.

(6) Because the grate bars become red hot, even on their inner surfaces, they heat the air both by conduction and radiation, while any radiant heat not absorbed by the air during a given pass across a grate bar is reflected back and forth until it has been absorbed.

(7) Because of the large fiow capacity of the grate bars and the high rate at which the air travels through the grate bars, a volume of air equal to the volume of a good sized room, say about 2,300 cubic feet, passes through the grate bars every quarter hour.

(8) The hot air delivered to the room is not permitted to accumulate in the vicinity of the fireplace.

(9) That portion of the heated air delivered to the room which does remain in the vicinity of the fireplace is prevented from escaping into the fireplace opening above the grate by the glass doors, except when the escape of heat or the checking of the fire is definitely desired. -If the room does become objectionably overheated, the fans will be automatically shut off and the doors may be opened. The other drafts may also be adjusted to promote desired conditions.

(10) The damper slide bars provided in the box 26 afford a very precise measure of control. The lines of openings can be uncovered progressively and selectively, depending upon the current intensity of the fire, the temperature condition in the room, and the relative intensity of the fire in the right and left sides of the fireplace.

We have described what we believe to be the best embodiments of our invention. We do not wish, however, to be confined to the embodiments shown, but what we desire to cover by Letters Patent is set forth in the appended claims.

We claim:

1. A portable and removable fireplace unit adapted for application to a finished conventional open fireplace without modification of the fireplace structure, and without requirement for attachment thereto, which includes (a) a combined complete, fire-supporting grate and heat exchanger consisting substantially in its entirety of sets of horizontally disposed, communicating hollow grate bars of substantial flow capacity with the grate bars all at a common level just above the fioor level and with the grate bars of each set rigidly connected end to end and closely packed to describe a continuous, tortuous course having a succession of acutely sharp turns, in which, by virtue of the successive sharp changes of direction the transient air is effectively mixed and impartially exposed to contact with the internal surfaces of the bars, each set having an open intake end facing toward the room for receiving air from the room in which the fireplace is situated and an open discharge end discharging toward the room for returning air to the room, said grate bar sets constituting essentially the sole fuel supporting means, and substantially the sole conductive heat interchange means, through which the room air is heated by the fire, and

(b) means associated with the grate bar sets for effecting a forced flow of air from the room, thrOugh said grate bar sets, and back to the room, all at or near floor level,

the construction and arrangement being such that the fireplace opening above the grate may be substantially devoid of hardware, and may therefore be free and uncluttered.

2. A fireplace unit as set forth in claim 1 which further includes (c) means for separately controlling and limiting admission of room air to the combustion field of the fireplace above the grate and from below the grate, including a supporting portion adapted to engage and to bear continuously on the hearth immediately in front of the fireplace opening and a framing portion which marginally engages the face of the fireplace above and at both sides of the fireplace opening, and which further includes (d) a set of triangularly related supporting legs connected to the combined grate and heat exchanger, and forming parts thereof, and

(e) means for individually and independently adjusting the legs heightwise relative to the combined grate and heat exchanger to provide a stable, multiple point support for said combined grate and heat exchanger consistent with the support provided for the unit by the hearth engaging portion thereof.

3. A fireplace unit as set forth in claim 2 in which the entire unit, excepting the grate bars and the supporting legs therefor, is constructed and arranged to rest on the hearth and in front of the fireplace opening.

4. A fireplace control and heat exchange unit, as set forth in claim 3, in which the lower front portion of the unit provides air transmitting passages in line, respectively, with the intake legs and with the dicharge legs of the combined grate and heat exchanger sections, and in which the spaces intervening between the intake and discharge passages of each of said sections is provided with damper means for regulating the admission of combustion air to the fireplace opening beneath the grate.

5. A fireplace control and heat exchange unit, as set forth in claim 4, in which the damper means referred to includes in each instance bridging stationary walls having horizontal rows of air admission openings in them with the spaces between passages exceeding in width the passages themselves, damper slides for the respective horizontal rows of openings, each having horizontal rows of openings corresponding in shape, size and spacing to the plate openings which they are designed to control, means carried on the inner face of each wall, and supporting and confining the slides with capacity only for horizontal movement along the walls, and operating finger pieces afi'ixed to the respective slides and protruding through slots formed in the walls into accessible positions.

6. A fireplace unit as set forth in claim 1 in which the means for effecting forced flow of air from the room through the grate bars consists of means for delivering air to the respective grate bar sets at the same pressure and velocity and in the same volume, and in which the grate bar sets are of the same size, length and configuration, for promoting equal volumes and velocities of delivery of air by the sets, equal times of air travel through the sets, and equal exposure to absorption of heat by the air passing through the respective sets.

References Cited UNITED STATES PATENTS 2,048,675 7/1936 Baruch et al 126132 2,369,044 2/1945 Hallinan 236-40 2,743,720 5/1956 Dollinger 126-121 2,828,078 3/1958 Snodgrass l26l2l X 3,001,521 9/1961 Reilly 126-121 3,240,206 3/1966 Schutt 12612l 2,359,197 9/1944 Brooks l26121 FOREIGN PATENTS 556,543 10/1963 Great Britain.


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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4008706 *Jun 27, 1975Feb 22, 1977Buanno John MFireplace furnace
US4085727 *Jun 30, 1976Apr 25, 1978Gillpatrick Sherman RAir circulating heater for fireplaces
US4112914 *Aug 20, 1975Sep 12, 1978Brown Rex MCombined fireplace hood and heating unit
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US5904137 *Jun 17, 1997May 18, 1999Salley; DwightFireplace heat exchanger
US5983890 *Jan 9, 1998Nov 16, 1999Canadian Gas Research InstituteFireplace having multi-zone heating control
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U.S. Classification126/521
International ClassificationF24B1/188, F24B1/00
Cooperative ClassificationF24B1/1886
European ClassificationF24B1/188F2