Construction heater and method of manufacture of heater

A gas-fired construction heater which meets the applicable ANSI Standard and operates to supply heated air separately from products of combustion. The products of combustion are permitted to contain no more than a specified percent of carbon monoxide when uncontrolled heater operating conditions are within predetermined ranges. The uncontrolled operating conditions include variations in input rate and supply voltage. A combustion chamber produces the products of combustion and has primary and secondary combustion zones. A heat exchanger receives the products of combustion and transfers heat therefrom to fresh air to be heated. The chamber and the heat exchanger define a tertiary combustion zone. Inlets supply a separate natural combustion draft to each of the primary and tertiary combustion zones. The inlets include a first and a third fixed-area inlet for respectively supplying the separate natural drafts to the primary and tertiary combustion zones. An additional fixed-area inlet supplies forced draft and natural draft to the secondary combustion zone. The fixed-area of each of these inlets is selected so that the specified percent is not exceeded during operation of the heater when the uncontrolled variation of either the input rate or the supply voltage is within its respective predetermined range. When the uncontrolled variations are outside of the respective predetermined ranges, the heater is turned off.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to heaters for construction sites and more 
particularly to providing a gas-fired construction heater that complies 
with nationally-recognized standards. 
2. Discussion of Prior Art 
In the past, a major telephone company approved certain types of gas-fired 
construction heaters based on its standards (the "Bell Standards"). 
Heaters complying with such standards are referred to in the manual 
"Outside Plant Construction--Safety, Tools, General;" No. 200-326, Issue 
2, December 1979, published by Western Electric Company, Incorporated for 
American Telephone and Telegraph Company. Such heaters were used by many 
telephone operating companies in the maintenance of telephone equipment. 
Such operating companies would only purchase heaters that had such 
approval. Therefore, manufacturers sought such approval for their 
gas-fired construction heaters. 
There have been major changes in the organization of the major telephone 
company in the United States of America. One result of these changes is 
that no single telephone company continues to set a nationally-recognized 
standard for these types of gas-fired construction heaters. Consequently, 
manufacturers of such heaters have sought a different way of assuring 
their customers that such types of heaters are suitable for the customers' 
purposes, such as construction and use in maintaining telephone equipment. 
For example, for one type of gas-fired construction heater sold in the 
United States of America, one possible way of providing such assurance is 
to design the gas-fired construction heater so as to comply with 
applicable standards of the American National Standards Institute 
("ANSI"). The current ANSI Standard for gas-fired construction heaters is 
identified as ANSI Z83.7b-1989 (the "ANSI Standard"). The ANSI Standard is 
used by equipment certifying organizations, such as the American Gas 
Association and the Underwriters Laboratories. These organizations test 
equipment, such as gas-fired construction heaters, and certify the 
equipment if the equipment meets the ANSI Standard. As to gas-fired 
construction heaters to be sold in Canada, the Canadian Gas Association 
("CGA") has established many standards, which currently are different from 
the ANSI Standard. 
However, the ANSI Standard is in a number of respects more stringent than 
both the Bell Standards and the current CGA standards. For example, the 
ANSI Standard will not permit a gas-fired construction heater to have a 
manually adjustable primary combustion air inlet. As a result, personnel 
using a gas-fired construction heater conforming to the ANSI Standards in 
the field will not be able to adjust primary combustion air flow in the 
heater according to actual field conditions. 
Further, the ANSI Standard requires such a gas-fired construction heater to 
either operate acceptably or shut itself off, and the acceptable operation 
must occur despite variations in uncontrolled operating conditions within 
predetermined ranges. For example, gas-fired construction heaters are 
designed using a standard heat value of 2500 BTU per cubic foot of propane 
burned. A gas-fired construction heater that is so designed and "rated" 
for 45,000 BTU would burn 18 cubic feet of propane per hour. That amount 
of propane would be supplied by selecting (1) the size of the burner 
orifices and (2) the standard gas pressure in the manifold ("manifold 
pressure") that supplies gas for the burner, with the selections taking 
into consideration the barometric pressure under which the burner is to 
operate. The term "input rate" as used herein indicates fuel supply to the 
burner at a standard manifold pressure for a particular size burner 
orifice, a known heat value of the fuel, operation of the burner at a 
specified barometric pressure and for a given temperature of fuel admitted 
to the burner. The "normal input rate" is the input rate of such heater as 
specified by the manufacturer of such heater. The ANSI Standard requires 
gas-fired construction heaters to operate in a range of from 85% to 112% 
of the normal input rate without producing more than 0.08% carbon monoxide 
("CO") air-free in a random sample of the combustion products of the 
gas-fired construction heaters (the "CO Standard"). Thus, the range in 
which the input rate of the gas-fired construction heaters must operate 
while meeting the CO Standard is said to be "predetermined" and varies 
from 85% to 112% of the normal input rate. The term "reduced rate" as used 
herein indicates fuel supply at 85% of the normal input rate, and the term 
"increased rate" indicates fuel supply at 112% of the normal input rate. 
Air supplied to the gas-fired construction heaters is another uncontrolled 
operating condition to which the more stringent ANSI Standard relates. 
Gas-fired construction heaters may have a blower that supplies fresh air 
to a heat exchanger which heats the air. The blower may also supply 
combustion air to the burner. Since gas-fired construction heaters are 
used at construction sites at which portable electric generators are used, 
the blowers are generally driven by an electric motor. Because such 
portable electric generators tend to output variable voltage, the ANSI 
Standard requires gas-fired construction heaters to operate in a range of 
from 85% to 110% of a standard supply voltage without exceeding the CO 
Standard. Thus, the gas-fired construction heaters must operate and meet 
the CO Standard in response to a range of such voltage that is said to be 
"predetermined" and varies from 102 VAC to 132 VAC if a standard supply 
voltage of 120 VAC is used. The term "reduced voltage" as used herein 
indicates that 85% of the standard supply voltage is supplied to the 
heater, and the term "increased voltage" means that 110% of the standard 
supply voltage is supplied to the heater. 
Since the voltage is used by the heater to drive the blower, supply voltage 
variations result in changes in the pressure of the fresh air and the 
combustion air supplied by the blower. In this sense, there would be a 
"predetermined" range of pressure of such air corresponding to the 
predetermined range of the supply voltage. 
Finally, the ANSI Standard requires the controls of gas-fired construction 
heaters to shut the burner off before the CO Standard or an upper 
temperature limit is violated. For example, the burner must shut off at 
the appropriate point as more and more area of the fresh air inlet and/or 
the heated air outlet is blocked. In testing such heaters, such blocking 
is done by successively placing pieces or strips of 1.5 inch wide adhesive 
tape across each inlet and/or outlet. This is referred to as the "strip 
method." Alternatively, one may use an iris-type orifice which 
symmetrically restricts air flow through such inlet or outlet. 
The problem Applicants faced, and which the present invention solves, is 
the provision, in a gas-fired construction heater which keeps the heated 
fresh air separate from the products of combustion ("furnace-type"), of 
structure which enables the heater to meet the ANSI Standard, and 
especially the CO Standard. Prior patents and so-called salamander heaters 
(which mix the heated fresh air and the products of combustion--and which 
meet the CO Standard) of which Applicants are aware have not appreciated 
the problem of providing a furnace-type gas-fired construction heater 
which meets the ANSI Standard. 
An example is Pelsue U.S. Pat. No. 4,108,143. Although this patent 
recognizes the goal (in a skid-mounted cable maintenance heater) of 
efficient use of BTUs, it does discussed, and no tertiary air is supplied 
to complete the combustion. 
Morris U.S. Pat. No. 3,765,398 relates variations of external wind 
conditions to variations in air flow to a burner. Morris provides an 
air-flow responsive air valve that shuts an air inlet to the burner's air 
blower when a gust of wind is sensed. 
Ito, et al U.S. Pat. No. 3,757,767 appreciates a "lifting" problem, where 
the flame lifts off the burner, but solves it by selecting the size of 
flame holes 35. Secondary air is supplied parallel to the flame from a 
chamber. 
Weiss U.S. Pat. No. 3,747,586 shows a solution to a different problem, and 
the solution (a variable port to a pilot) is contrary to the ANSI 
Standard. Weiss also shows a variable shutter to control air to the 
burner, contrary to the ANSI Standard. 
Mayo U.S. Pat. No. 2,561,934 uses an adjustable primary air damper and 
directs forced air via a tube onto a flame. This shows a lack of 
appreciation of the ANSI Standards problem. 
Velie U.S. Pat. No. 4,848,313 has a goal of improving efficiency of 
combustion and getting mor BTU output/cubic inch of heater. Velie shows 
primary and secondary air inlets below a flame spreader that is above a 
burner. 
Velie U.S. Pat. No. 4,651,711 has a main concern of providing a removable 
burner. Velie uses a flame spreader without air holes at the flame tips. 
The air inlet is only at one side of the flames and there is no heat 
exchanger. 
Yagisawa U.S. Pat. No. 4,427,367 is directed to avoiding carbon build-up on 
a fuel nozzle. Air is fed in an annular flow around a plate and along a 
nozzle and through the plate via openings to prevent carbon build-up. 
Jalics U.S. Pat. No. 4,221,557 has a primary goal of sensing improper 
combustion conditions at a main burner, and turning the main burner off 
before its flame extinguishes. Jalics uses a secondary burner which 
extinguishes just before the main flame starts to operate in an incomplete 
combustion mode. Jalics does not refer to the ANSI Standard, and does not 
appreciate the requirements thereof as shown by the use of a variable air 
scoop. 
SUMMARY OF THE PRESENT INVENTION 
The present invention solves the problem of providing a gas-fired 
construction heater which meets the ANSI Standard. Applicants' analysis 
indicates that in a furnace-type gas-fired construction heater the term 
"draft" may be used to denote the flow of air from a plenum to the burner 
in the combustion chamber, where such air flow results from the pressure 
drop across an air inlet that is between the plenum and the burner. Also, 
"natural draft" may be used to denote draft caused or induced by the 
pressure drop from (1) the flow of combustion products out of the 
combustion chamber (resulting from combustion) and (2) the static air 
pressure in the plenum. Finally, "forced draft" may be used to denote 
draft caused by the pressure drop resulting from the velocity of the air 
as it flows into the plenum and impinges on a wall of the combustion 
chamber which is provided with the air inlet. Since forced draft is 
dependent on air velocity, "blocking" of forced draft refers to diverting 
such flow of air or otherwise preventing such flow of air from impinging 
on or flowing through such air inlet. Applicants' analysis also indicates 
that there are three combustion zones in the furnace-type gas-fired 
construction heater (primary, secondary and tertiary). 
With this in mind, according to the principles of the present invention 
forced draft to the primary and tertiary zones is fully blocked, forced 
drafts to the secondary zone are partially blocked, and selected amounts 
of natural drafts are provided to the combustion chamber via separate 
fixed-area air inlets for each of such combustion zones. Thus, there are 
natural drafts to the primary and tertiary zones, and combined forced and 
natural drafts to the secondary zone. A burner control is set with respect 
to air pressure at the entrance to the plenum and a selected heated air 
upper temperature limit. The heated air outlet has a selected fixed area. 
In use, the heater of the present invention either 
(1) operates: 
(a) within the predetermined range of the input rate, 
(b) within the predetermined supply voltage range, and 
(c) with limited blockage of either the fresh air inlet or the heated air 
outlet while meeting the CO Standard and being below the upper temperature 
limit, or 
(2) stops operating because the burner is shut off before the upper 
temperature limit is exceeded or the combustion products fail to meet the 
CO Standard, which shut off occurs under uncontrolled conditions that 
cause: 
(a) the input rate or the supply voltage to be outside of their respective 
predetermined ranges, or 
(b) the upper temperature limit to be reached. 
An object of the present invention is to provide a heater which meets a 
selected operating standard. 
A further object of the present invention is to provide a gas-fired 
construction heater which meets the ANSI Standard. 
A related object of the present invention is to provide a furnace-type 
gas-fired construction heater which meets the ANSI Standard. 
Another object of the present invention is to provide separate combustion 
air inlets to each of three combustion zones in a gas-fired construction 
heater. 
Still another object of the present invention is to provide selected forced 
and/or natural draft to each of three combustion air inlets to a gas-fired 
construction heater to render such heater able to operate in compliance 
with the ANSI Standard. 
Yet another object of the present invention is to control the burner of the 
gas-fired construction heater so that the burner is shut off before the CO 
Standard is exceeded if any of the following should occur: (1) excessive 
blockage of the air inlet to, or of the heated air outlet from, the 
gas-fired construction heater; (2) voltage supplied to the heater is 
outside of its predetermined range, or (3) the input rate is outside of 
its predetermined range. 
A still further object of the present invention is to identify steps for 
modifying a standard furnace-type gas-fired construction heater to render 
it capable of operating in compliance with the ANSI Standard. 
With these and other objects in mind, the present invention solves such 
problem by providing a gas-fired construction heater which meets the ANSI 
Standard and operates to supply heated air separately from products of 
combustion. The products of combustion are permitted to contain no more 
than a specified percent of a selected chemical compound when uncontrolled 
heater operating conditions are within predetermined ranges. The 
uncontrolled operating conditions include variations in the input rate and 
variations in the voltage supplied to the heater. Since such voltage is 
applied to a blower that supplies fresh air to the heater, a resulting 
uncontrolled operating condition is the pressure of the fresh air supplied 
to a heat exchanger and to a plenum of the heater. 
The heater includes a combustion chamber for producing the products of 
combustion, the chamber having primary and secondary combustion zones. A 
heat exchanger receives the products of combustion and transfers heat 
therefrom to fresh air to be heated. The combustion chamber and the heat 
exchanger define a tertiary combustion zone. Inlets supply a separate 
natural air draft to each of the primary and tertiary combustion zones. 
The inlets include a first and third fixed-area inlets for respectively 
supplying the separate natural drafts to the primary and tertiary 
combustion zones. Additional fixed-area inlets supply forced draft and 
natural draft to the secondary combustion zone. The fixed area of each of 
these inlets is selected so that the specified percent is not exceeded 
during operation of the heater when the uncontrolled variations of the 
input rate and the supply voltage (hence the fresh air pressure) are each 
within their respective predetermined ranges. 
Another aspect of the present invention relates to modifying a standard 
gas-fired construction heater to meet the ANSI Standard. One such standard 
gas-fired construction heater has a plenum that receives forced draft 
which is unblocked and supplied to both a primary combustion zone and a 
secondary combustion zone of a combustion chamber. A variable air inlet in 
a first wall of the combustion chamber admits the forced draft to the 
primary zone, and no air inlet is provided directly to a tertiary 
combustion zone. A burner is also provided for supplying the gas. The gas 
is ignited in the combustion chamber and produces products of combustion. 
A closed duct has an inlet for receiving the combustion products and an 
exhaust outlet for discharging the combustion products. A housing guides 
air to be heated over the closed duct. The heated air is discharged from 
the housing. A blower supplies forced air to the housing and to the 
plenum. A pressure sensor monitors the pressure of the forced air from the 
blower and enables the burner to operate when the air pressure exceeds a 
relatively low limit (i.e., 0.2 inches of water). A thermal sensor 
responds to the temperature of the heated air and of the closed duct. 
Such standard heater is modified according to the principles of the present 
invention by providing facilities for rendering the modified heater 
capable of operating without manual adjustment of the supply of the 
primary combustion forced draft. Such operation of the modified heater is 
in compliance with a selected standard, such as the ANSI Standard, which 
does not permit such manual adjustment, but which does limit the maximum 
percent of the given chemical compound (such as CO) which is permitted to 
exit the exhaust outlet when any of the following occur: 
(1) the input rate varies in the predetermined input rate range, 
(2) the supply voltage varies in the predetermined supply voltage range, 
and 
(3) the forced air inlet or the heated air outlet become blocked, 
as is more fully discussed below. 
The facilities include a baffle mounted close to the first wall of the 
combustion chamber for blocking the forced draft in the plenum so that 
only the natural draft enters the primary combustion zone of the 
combustion chamber and only partial forced draft enters the secondary 
combustion zone. Combustion air inlets, which may be provided in the first 
wall of the combustion chamber and/or in the closed duct, have separate 
fixed inlet areas. The primary air inlet is enlarged and admits the 
natural draft to the primary combustion chamber. Secondary air inlets are 
enlarged and partially covered by the baffle to admit both the forced 
draft and the natural draft to the secondary zone. Tertiary air inlets are 
provided for supplying the natural draft to the tertiary combustion zone. 
The secondary air inlets and the tertiary air inlets are provided in the 
first wall at a plurality of locations that are progressively further and 
further from the primary air inlet. The pressure sensor is set to open a 
first switch when the pressure of the forced air decreases below a 
specified pressure, which is the lowest fresh air pressure at which the 
maximum percent of the given chemical compound does not appear in the 
combustion products exiting the exhaust outlet. The thermal sensor is set 
to open a second switch in response to the temperature of the air in the 
closed duct and heat from the closed duct being at a maximum value. That 
value is selected to permit the input rate supplied to the burner to be at 
a maximum (as required by the selected standard) when the forced air 
pressure is at the lowest amount. A controller is responsive separately to 
the opening of the first switch or to the opening of the second switch for 
interrupting the operation of the burner. The interruption of the burner 
occurs as a result of either or both of the uncontrolled operating 
conditions being outside of the respective predetermined range or blockage 
of the fresh air inlet or the heated air outlet beyond a limit.

GENERAL DESCRIPTION OF THE INVENTION 
A heater 20 and a method of the present invention are described with 
respect to the ANSI Standard referred to above. The heater 20 is said to 
conform to the ANSI Standard, and testing of the heater 20 is described to 
illustrate compliance with the CO Standard. 
Referring to FIG. 1, the heater 20 is shown having a combustion chamber 21 
connected to an exhaust inlet 22 of a heat exchanger 23. The volume of 
space in the combustion chamber 21 in which combustion initiates is 
referred to as a primary combustion zone 24. The primary combustion zone 
24 extends to a secondary combustion zone 25 adjacent a plurality of 
spaced flames 26. From the secondary combustion zone 25 upward and within 
a closed duct 27 past the exhaust inlet 22 of the heat exchanger 23, there 
is a tertiary combustion zone 28. The combustion chamber 21 is mounted in 
a plenum 29 that receives forced combustion air (shown by arrow 30). The 
combustion air 30 flows in the plenum 29 toward a first wall 32 of the 
combustion chamber 21 (in the direction of arrow 31). A baffle 33 is 
provided in the plenum 29 closely adjacent to the first wall 32 to block 
the forced air 30 so it cannot flow directly to the wall 32 adjacent to a 
primary air inlet 34. The primary air inlet 34 has a fixed area and is 
formed in the first wall 32 behind the baffle 33 to supply natural primary 
combustion draft 35 to a burner 36 to support combustion in the primary 
combustion zone 24. This supports the flames 26, which extend upwardly 
through the secondary combustion zone 25 toward the exhaust inlet 22 to 
the closed duct 27 of the heat exchanger 23. 
A series 37 (FIGS. 7 and 8) of secondary combustion air inlets 38 is 
provided in the wall 32 of the combustion chamber 21. Each secondary inlet 
38 is located between adjacent ones of the flames 26 near tips 39 thereof. 
The secondary inlets 38 supply secondary combustion drafts (see arrow 40) 
to support combustion in the secondary zone 25. An upper edge 41 of the 
baffle 33 is vertically aligned with the center of the secondary inlets 38 
so that the baffle 33 blocks half of the forced air 30 flowing to the 
secondary inlets 38. As a result, the secondary combustion draft 35 is 
both forced draft and natural draft. 
The flames 26 extend upwardly from the secondary zone 25 to the tertiary 
combustion zone 28. Tertiary combustion air inlets 42, which are shown in 
detail in FIG. 6 provided in a wall 43 of the closed duct 27 of the heat 
exchanger 23, admit natural tertiary combustion draft (shown by arrow 45) 
to the closed duct 27 to support combustion therein. The heat exchanger 23 
has a heated air outlet 44. 
Fuel 46 is supplied to the combustion chamber 21 from a manifold 47. A 
manifold gauge 48 (FIG. 2) is shown for indicating manifold pressure, 
which is the pressure of the fuel 46 in the manifold 47. 
A blower 49 is provided for causing the forced air 30 to flow in the plenum 
29 and past the closed duct 27 to exit the heater 20 via the heated air 
outlet 44. A pressure sensor 50 indicates the pressure of the forced air 
30 at an entrance 50A to the plenum 29. The blower 49 is driven by an 
electric motor 51. Voltage (see signal 52 in FIG. 3) supplied to the 
heater 20 may vary from a standard 120 VAC and drives the motor 51. 
The areas of the respective primary, secondary, and tertiary inlets 34, 38 
and 42 are selected to enable the heater 20 to meet the CO Standard even 
though: 
(1) the input rate (generally indicated by the manifold gauge 48) varies 
within the above-described predetermined input rate range, and 
(2) the voltage 51 varies in the above-described predetermined supply 
voltage range. 
To comply with the ANSI Standard, the burner 36 must shut off before 
products of combustion 53 exceed the limit set by the CO Standard for the 
chemical compound, such as CO. For this purpose the pressure sensor 50 is 
set to open a first or air pressure switch 53A (FIG. 13) when the air 
pressure at the entrance 50A to the plenum 29 decreases below a specified 
pressure. Also, a thermal sensor 54 responds to the temperature of the 
forced air 30 flowing past the closed duct 27 and to the temperature of 
the closed duct 27 of the heat exchanger 23. The thermal sensor 54 
controls a normally closed switch 55 (FIG. 13) which opens when the 
temperature sensed indicates that the temperature of the closed duct 27 
exceeds an upper temperature limit. In response to either or both the 
opening of the air pressure switch 53A or the opening of the thermal 
sensor switch 55, a burner control 56 (FIG. 13) closes a fuel valve 57 
(FIG. 13) which stops the flow of the fuel 46 to the burner 36, rendering 
the burner 36 inoperative. 
As modified, the heater 20 of the present invention either: 
(1) operates 
a. within the predetermined input rate range, 
b. within the predetermined supply voltage range, and 
c. with limited blockage of either a fresh air inlet 58 or the heated air 
outlet 44, or 
(2) operates as in (1) until the occurrence of uncontrolled conditions that 
cause: 
a. the input rate or the supply voltage to be outside of their respective 
predetermined ranges, or 
b. the upper temperature limit to be reached, 
whereupon the heater 20 stops operating because the burner 36 is shut off 
before the combustion products 53 fail to meet the CO Standard. 
DETAILED DESCRIPTION OF HEATER 20 
With the general description in mind, reference is made to FIGS. 2 and 3 
which show two embodiments of the heater 20. Embodiment one, referred to 
using the reference 20A, is shown in FIG. 2 for use with an auxiliary 
blower 49A, such as the Model 1325B sold by the T. A. Pelsue Company. 
Embodiment two, referred to using the reference 20B, is shown in FIG. 3 as 
having the blower 49B integral with the heater 20B. 
In each case, the heater 20A or 20B is supplied with the voltage 52 which 
may vary beyond the above-described predetermined range, which was 
described as being from 102 VAC to 132 VAC relative to the standard value 
of 120 VAC. 
For purposes of describing the present invention, the heater 20A (FIG. 2) 
will be described, it being understood that the heater 20B (FIG. 3) is 
provided with structure and operation similar to that of the heater 20A, 
except for the integral nature of the blower 49B and as noted below. The 
blowers 49A and 49B are protected by a screen 58 and force the air 30 
through a fresh air inlet 59A having a fixed area. A corresponding fresh 
air inlet 59B is shown in FIG. 3. 
The fresh air inlet 59A may become blocked during use of the heater 20A, 
such as by a piece of paper being sucked against the screen 58. This is 
simulated in testing performed to determine compliance of the heater 20A 
with the ANSI Standard. In the test using the strip method, strips 60 of 
tape are successively placed on the screen 58 to partially block the fresh 
air inlet 59A. 
Continuing to refer to FIGS. 1 and 2, a heater housing 61 contains the heat 
exchanger 23, the burner 36, the combustion chamber 21 and the plenum 29. 
The plenum 29 extends from the entrance 50A (on the right in FIG. 2) to 
the first wall 32 of the combustion chamber 21 (on the left in FIG. 1). A 
control unit 62 positioned outside the housing 61 houses the controller 56 
and other standard items, such as an "on/off" switch 63 (FIG. 4). 
Referring to FIGS. 4 and 5, the heat exchanger 23 of the heater 20A is 
shown in greater detail. The heat exchanger 23 may be fabricated from 304 
stainless steel to permit it to operate at a high (e.g., 1200 .degree. F.) 
temperature. The closed duct 27 extends in a serpentine path from the 
inlet 22 to exhaust stacks 64 which extend through the housing 61. A lower 
section 65 of the closed duct 27 extends horizontally, front-to-back in 
the housing 61 and divides the forced air 30 into a combustion air flow 
path (see arrow 66) and a fresh air flow path (see arrow 67 in FIG. 1). 
The products of combustion 53 flow in and heat the closed duct 27. The heat 
is transferred to the air in the fresh air path 67, which exits the 
housing 61 through the heated air outlet 44. The outlet 44 is shown in 
FIG. 10 as having a circular shape, a diameter 44A, and has an area 
selected as described below. A screen 69 is placed over the outlet 44. 
In the use of the heater 20, equipment (not shown) may be placed next to 
the outlet 44, or other items may block the flow of heated air (shown by 
arrow 70) from the housing 61. Similarly, a flexible duct 101 (FIG. 3) may 
be attached to the heated air outlet 44, and such duct 101 may become 
blocked. When either event occurs, the flow of the forced air 30 in the 
fresh air path (arrow 67) decreases and less heat is transferred from the 
closed duct 27. As a result, the temperature of the closed duct 27 
increases and is sensed by the thermal sensor 54. 
Considering FIG. 5, 7, 8 and 9, the combustion air flow path 66 extends in 
the direction of the arrow 31 under the lower section 65 within the plenum 
29 of the housing 61. The forced air 30 is thus directed toward the first 
wall 32 of the combustion chamber 21. A base 72 secured to the housing 61 
supports the combustion chamber 21 and the baffle 33. The baffle 33 has an 
L-shape and is fixed to the base 72 to provide a space 73 between the 
first wall 32 and the baffle 33. The baffle 33 extends horizontally (FIGS. 
7 and 8) across the wall 32 from a left side 74 (FIG. 8) to a right side 
75 and covers the primary combustion air inlet 34. In this manner, none of 
the forced air 30 enters the primary inlet 34. Rather, according to the 
static air pressure in the plenum 29, the natural draft 35 flows into the 
primary air inlet 34. The upper edge 41 of the baffle 33 is shown in FIG. 
8 extending horizontally in alignment with the centers of the secondary 
inlets 38. 
Referring now to FIGS. 8 and 9, the burner 36 and the combustion chamber 21 
are shown fabricated from a casting 76. The burner 36 includes a bore 77 
extending from one end 78. The end 78 is plugged after drilling the bore 
77. The bore 77 intersects a transverse bore 79 that is tapped to receive 
a fuel supply fitting 80. The fitting 80 is connected via standard fuel 
supply components 80A (FIG. 2) to the fuel valve 57 (FIG. 13) and to a 
fuel tank (not shown). The bore 77 forms the manifold 47. The pressure 
(manifold pressure) of the fuel 46 in the manifold 47 may be indicated by 
the fuel pressure gauge 48 (FIG. 2) which may be connected to a gauge port 
80B (FIG. 2). Fuel supply holes 81 are drilled in the casting 76 at spaced 
locations at which it is desired to position the flames 26. A fuel orifice 
82 (e.g., a fixed gas orifice) of a selected size, such as #59, is 
received in each hole 81 to regulate the amount of fuel 46 supplied to the 
combustion chamber 21. The fuel orifice 82 is selected according to the 
particular fuel 46 that is to be burned. For example, gas vapor fuels such 
as butane, compressed natural gas or propane may be burned. 
The combustion chamber 21 is formed by the first wall 32 and by walls 83 of 
the casting 76. A top 84 of the casting 76 is open to allow the products 
of combustion 53 to flow into the exhaust inlet 22 of the heat exchanger 
23. The primary combustion air inlet 34 includes an elongated opening 85 
cast through the first wall 32 and extending horizontally past each of the 
end fuel supply holes 81E. The inlet 34 also includes a shutter 86 that is 
wider and longer than the opening 85 and that covers a selected portion of 
the opening 85. The shutter 86 is fixed to the casting 76 so that the area 
of the primary combustion air inlet 34 is fixed at a selected value as 
discussed below. The primary air inlet 34 is vertically aligned with and 
extends across the bases 87 of the flames 26 to provide the primary 
natural draft 35 to the primary combustion zone 24 at the lower portion of 
the combustion chamber 21. 
With the fuel 46 supplied to the orifices 82 and the primary draft 35 
supplied from the inlet 34, an igniter 88 is effective to ignite the 
air-fuel mixture to form the flames 26. When a flame sensor 89 (FIG. 5) 
senses the flames 26, it causes the controller 56 (FIG. 13) to keep the 
valve 57 open, whereas when the flames 26 are out, the sensor 89 causes 
the controller 56 to shut the valve 57. 
The flames 26 also require the secondary combustion drafts 40 for proper 
combustion that meets the CO Standard. For this purpose, the secondary 
combustion air inlets 38 are provided in the form of horizontal holes 90 
(FIG. 9) drilled through the first wall 32 to which the shutter 86 is 
attached. The area of each hole 90 is as described below, and is a fixed 
area. The holes 90 are spaced horizontally and are parallel to the 
longitudinal axis 91A of the opening 85. Each hole 90 is centered along a 
line 91B extending vertically and bisecting the space between the holes 
81. The upper edge 41 of the baffle 33 is vertically aligned with the 
center of the holes 90. In this manner, the baffle 33 blocks half of the 
forced draft 30 flowing toward the holes 90, such that a reduced flow of 
the forced air 30 is permitted to flow over the upper edge 41 and through 
the holes 90 as the drafts 40. As a result, the secondary combustion 
drafts 40 include reduced flow of forced air 30 and the natural draft, 
which are supplied through the holes 90 into the secondary combustion zone 
25. 
The tertiary combustion zone 28 extends from just above the secondary air 
inlets 38 vertically through the exhaust inlet 22 into the lower section 
65 of the closed duct 27 of the heat exchanger 23. It may be observed in 
FIG. 1 that the secondary air inlets 38 and the tertiary air inlets 42 are 
located progressively further and further from the primary combustion air 
inlet 34. There are three embodiments of the tertiary combustion air 
inlets 42. 
FIRST EMBODIMENT OF TERTIARY COMBUSTION AIR INLETS 42 
Referring to FIGS. 5, 6 and 7, the first embodiment of the tertiary air 
inlets 42 is shown and these inlets are referred to as inlets 42A. The 
inlets 42A are in the form of many circular ports 92A (FIG. 7) in a bottom 
93 of the lower section 65, shown as the wall 43 in FIG. 5. The ports 92A 
are in a row as shown in FIG. 6, and are adjacent to an edge 94 of the 
exhaust inlet 22. The bottom 93 is parallel to the direction 31 of the 
forced air 30 such that there is no effective dynamic air pressure on the 
ports 92A. As a result the natural draft 45 enters the ports 92A to 
provide the tertiary combustion air to the tertiary combustion zone 28. 
The ports 92A are shown in FIG. 6 on an upstream side 95 of the exhaust 
inlet 22, but may be located on a downstream side 96 of the inlet 22. The 
number and size of the ports 92A are as described below. 
SECOND EMBODIMENT OF TERTIARY COMBUSTION AIR INLETS 42 
The second embodiment of the tertiary combustion air inlets 42 is shown in 
FIG. 12B. These inlets are referred to as inlets 42B and are provided as 
ports 92B formed in the first (front or right) wall 32 of the combustion 
chamber 21. The ports 92B serve the same function as the ports 92A, and 
are located adjacent to the exhaust inlet 22. Because the ports 92B are in 
the flow of the forced draft 30, a tertiary baffle 97B is secured to the 
wall 32 over the ports 92B and spaced from the bottom 93 for blocking the 
forced air 30, but allowing the natural draft 45 to enter the ports 92B. 
THIRD EMBODIMENT OF TERTIARY COMBUSTION AIR INLETS 42 
The third embodiment of the inlets 42 is shown in FIG. 12C. These inlets 
are referred to as inlets 42C and serve the same function as the inlets 
42A. The inlets 42C are in the form of ports 92C extending through an 
inclined section 98 of the bottom 93 of the lower section 65. The ports 
92C are spaced further from the inlet 22 than the ports 92B, but are 
higher relative to the inlet 22. Because the ports 92C are in the flow of 
the forced air 30, an inclined, tertiary baffle 97C is secured to the 
inclined section 98 closely spaced relative thereto for blocking the 
forced air 30, but allowing the natural draft 45 to enter the ports 92C. 
DESCRIPTION OF METHOD OF MODIFICATION OF STANDARD HEATER TO FORM THE HEATER 
20 
As an example of how a standard gas-fired construction heater may be 
modified to provide the heater 20 of the present invention, reference is 
made to FIGS. 11A-11C. The standard heater may be a Model 1690 heater sold 
by the T. A. Pelsue Company. As described above, the Model 1690 is used 
with an auxiliary blower 49A, which may be a Model 1325B sold by the T. A. 
Pelsue Company. In describing the modifications to the Model 1690, 
reference is made to the corresponding structural elements of the heater 
20, because, as modified according to all of the Steps 1-31 in which 
modifications were made, the Model 1690 became the heater 20. 
The standard heater is rated at 52,000 BTU and burns 20.8 cubic feet of 
propane fuel 46 per hour. The burner orifices of the Model 1690 are #56 
and are used with a standard manifold pressure of ten inches of water at 
normal input rate. The blower 49 of the Model 1325B operates at a standard 
voltage of 115 VAC. The area of the primary combustion air inlet 34 is 
0.3066 square inches (4.38 by 0.070 inches), and forced air 30 is applied 
directly against the combustion chamber wall that corresponds to the first 
wall 32 of the heater 20. Further, a manually variable damper is provided 
in the form of a shutter (not shown) which is adjustably mounted on the 
first wall 32 partially over the opening 85, which shutter is referred to 
as the shutter 86M to distinguish it from the fixed shutter 86 of the 
present invention. The standard model 1690 gas-fired construction heater 
has the characteristics identified in Chart 1 below. 
CHART 1 
______________________________________ 
Model 1690 with Model 1325B 
______________________________________ 
Area of primary combustion 
nominally 0.3066 
air inlet 34 (variable) 
(0.07 in. .times. 4.38) 
(sq. in.) 
Area of secondary conbus- 
0.196 
tion air inlets 38 (sq. 
(4 holes @ .25 dia. each) 
in.) 
Area of tertiary combustion 
Zero 
air inlets (sq. in.) 
Upper temperature limit 
190 
(.degree.F.) read by thermal sensor 
54 
Baffle covers primary inlet 
None 
34 
Baffle covers 1/2 of 
None 
secondary inlets 38 
Normal supply voltage 52 to 
115 
heater 20 (VAC) 
Nominal air pressure 
0.6 
(entrance 50A to plenum 
29 - inches of water) 
Area of heated air outlet 
18.19 
44 (square inches) 
Rating of heater (BTU) 
52,000 
Burner orifice size and 
#56 (5) 
(number of orifices) 
CO in combustion products 
Less than 0.08% 
emitted from exhaust stacks 
CO air-free 
64 at normal conditions 
(115 VAC, normal input 
rate, normal voltage 52, no 
blockage of fresh air inlet 
59 or heated air outlet 
44). 
Manifold pressure at normal 
10 
input rate (inches of 
water) 
Compliance with CO Standard 
None 
Air pressure at which 
0.2 
pressure sensor 50 closes 
switch 53A (inches of 
water) 
______________________________________ 
By following the steps set forth in FIGS. 11A-11A and as described below, 
the operation of the Model 1690 (with the Model 1325B) was rendered in 
compliance with the CO Standard of the ANSI Standard. The following 
description not only indicates (1) the steps taken by Applicants to tests 
the Model 1690 to determine how the Model 1690 fails to meet the ANSI 
Standard, particularly the CO Standard, but (2) once a testing step is 
shown to not meet the CO Standard, indicates how the Model 1690 was 
modified to pass each particular test step. 
Testing Per CO Standard--Modifying Model 1690 
Step 1--Test at normal input rate 
Test Result: pass 
Step 2--Test at reduced rate 
Test Result: pass 
Step 3--Test at increased rate 
Test Result: fail 
Modifications 
3A--Derate from 52,000 BTU to 45,000 BTU. 
The action taken to pass this step was to derate the Model 1690 from 52,000 
BTU to 45,000 BTU. This was based on a nominal heat value of 2,500 BTU per 
cubic foot of propane fuel 46 burned by the standard heater at normal 
conditions. Under test conditions, the actual heat value was 2,380 BTU per 
cubic foot. This was equivalent to 20.8 cubic feet of propane fuel 46 
burned per hour. 
The derating to 45,000 BTU was achieved by changing to a number 59 orifice 
(corresponding to the orifices 82 of the heater 20) in all of the burner 
distributor holes 81 of the heater 20. The Model 1690 is now referred to 
as the derated heater (FIG. 11A). 
Step 4--Test at increased rate 
Test Result: pass 
With the number 59 orifices in the derated heater, the testing at increased 
rate met the CO Standard. 
Step 5--Test at reduced rate 
Test Result: pass 
With the number 59 orifices in the Model 1690, the CO Standard was met 
during a rerun of step 2, (testing at reduced rate). 
Step 6--Test at reduced voltage 
Initial Test Result: fail 
The standard supply voltage 52 was increased to 120 VAC, and in step 6 it 
was varied from the new nominal 120 VAC to 85% of nominal, or 102 VAC. 
Variation of this voltage 52 supplied to the derated heater resulted in 
variation of the number of cubic feet of fresh air flowing into the fresh 
air inlet 59A (FIG. 2). The failure to pass the CO Standard in this step 
indicated to Applicants that too little combustion air was supplied at 
reduced voltage. 
Modifications 
6A--increase area of primary air inlet 34. 
6B--add baffle 33. 
6C--reduce area of primary air inlet 34. 
Modification 6A retained the overall size of the opening 85 in the casting 
76, but adjusted the shutter 86M which, for testing, was adjustable. The 
adjustment provided a width of 0.1 inch for the primary combustion air 
inlet 34, compared to the original width of 0.070 inches. A trial test was 
conducted at reduced voltage, and the CO Standard was met. A trial test 
was then conducted at increased voltage (132 VAC) and the CO Standard was 
not met. 
Modification 6B positioned the baffle 33 at 0.14 inches from the wall 32 
and covering the primary air inlet 34. This blocked the flow of the forced 
air 30 to the primary air inlet 34, allowing the natural draft 35 to flow 
through the primary air inlet 34. The baffle 33 was positioned with the 
upper edge 41 blocking two-thirds of the secondary air inlets 38. The 
baffle 33 blocked most of the forced air 30 flowing toward the secondary 
combustion air inlets 38. This position of the baffle 33 allowed some of 
the forced drafts 40, but primarily the natural drafts 40, to enter the 
secondary combustion air inlets 38. During trial tests, the CO Standard 
was met at reduced voltage. 
Modification 6C reduced the area of the primary combustion air inlet 34 by 
moving the shutter 86M to reduce the effective width of the opening 85 to 
0.055 inches, and the CO Standard was met. 
Step 7--Test at reduced voltage 
Test Result: pass 
With the modification made in step 3 and with modifications 6B and 6C, the 
Model 1690 heater is referred to in FIG. 11A as the Modified Heater I. 
Upon retest in Step 7, the Modified Heater I met the CO Standard. 
Step 8--Test at increased voltage 
Test Result: pass 
The increased voltage 52 was 110% of the new nominal or standard 120 VAC, 
or 132 VAC. Notwithstanding the more stringent ANSI Standard, which does 
not permit manual adjustment of the primary air inlet 34, the 
modifications embodied in Modified Heather I were effective to enable the 
Modified Heater I to meet the CO Standard during the test in Step 8. For 
example, the ANSI Standard only allows use of fixed area primary air 
inlets, which Applicants achieve by using the fixed shutter 86. 
Step 9--Test at blocked inlet--normal input rate 
Test Result: pass 
"Blocked inlet" refers to sequentially decreasing the effective area of the 
fresh air inlet 59 of the Model 1690. If the strip method is used, this is 
done by applying one 1.5 inch wide strip 60 of tape across the screen 58 
and conducting the test (see FIG. 10 where strips 60 are placed over the 
outlet 44). If the CO Standard is met, another strip 60 or part of a strip 
60 of tape is applied and the heater must either meet the CO Standard and 
continue operating, or before the CO Standard is not met must shut down by 
turning the burner 36 off. The test in Step 9 was passed using one and 
one-half strips 60. The strips 60 were arranged with one strip 60 across 
the diameter of the screen 58 of the inlet 59, and the half strip 60 
forming a "T" with the first strip 60. When more strips 60 are used, they 
are placed over the screen 58 (or the outlet 44 in Step 20) in the 
configuration of an asterisk to block more of the effective area of the 
fresh air inlet 59. The one and one-half strips 60 blocked 27% of the area 
of the inlet 59. Additional blockage of the inlet 59 is referred to as 
"excessively blocked." 
Step 10--Test at blocked inlet--reduced rate 
Test Result: pass 
The taping steps described with respect to Step 9 (which applied one and 
one-half strips 60) were repeated. 
Step 11--Test at blocked inlet--increased rate 
Test Result: fail 
Modifications 
11A--Enlarge secondary air inlets 38 to 5/16" dia. 
11B--Lower baffle 33. 
11C--Reset pressure sensor 50 set point from 0.2 to 0.625 inches of water. 
Further testing at various percent blockage of the fresh air inlet 59 
indicated that more secondary combustion air was required. This was 
achieved by modification 11A which enlarged each of the four inlets 38 to 
5/16 inch. 
Next, the upper edge 41 of the baffle 33 was lowered to expose one-half of 
the area of the inlets 38 to the forced air 30. 
Upon further testing, it was found that at a pressure of 0.2 inches of 
water (sensed by the pressure sensor 50 in its current location/mounting) 
the burner 36 would turn on at 27% blockage of the fresh air inlet 59. At 
that amount of blockage and pressure at the entrance 50A, the CO Standard 
would not be met. The air pressure setting at which the pressure sensor 50 
would close the switch 53A was increased so that the switch 53A closed 
just before the CO Standard was violated when the maximum (27%) blockage 
occurred at increased rate. For the Model 1690, in the form of Modified 
Heater I with the modifications 11A and 11B, this pressure was 0.625 
inches of water. 
The Model 1690, with the modifications of Steps 3, 6 (Modifications 6B and 
6C) and 11, is now referred to as the "Modified Heater II". 
Step 12--Test at blocked inlet--increased rate 
Test Result: pass 
This is a retest of the test in Step 11. Step 12 is shown on FIG. 11A. 
Step 13--Test at reduced voltage 
Initial Test Result: fail (burner 36 would not turn on). 
Modifications 
13A--Enlarged the inside diameter of the heated air outlet 44. 
13B--Reset pressure sensor 50 set point from 0.625 to 0.55 inches of water. 
Modification 13A increased such diameter of the heated air outlet 44 from 4 
13/16 inches to 5 inches, to a new area of 19.63 square inches. 
With this modification, the Model 1690 is referred to as a "Modified Heater 
III" in FIG. 11B. 
Step 14--Test at reduced voltage 
Test Result: pass 
Modification 13A resulted in reducing the back pressure caused by the 
heated air outlet 44, reducing the static air pressure in the plenum 29, 
allowing the set point of the pressure sensor 50 to be reset. 
Step 15--Test at blocked inlet--increased rate 
Initial Test Result: fail 
This step is a repeat of the test of step 12. 
Step 16--Test at blocked inlet--reduced rate 
Initial Test Result: fail 
Modifications 
16A--Secured pitot tube 100 at fixed location. 
16B--Added tertiary air inlets 42 (ports 92C) and tertiary baffle 97C. 
16C--Substituted ports 92A for ports 92C, and baffle 97A for baffle 97C. 
Failure to meet the CO Standard in steps 15 and 16 lead to investigation of 
the mounting and location of the pitot tube 100. The pitot tube 100 was 
remounted at a fixed position with the open end thereof open toward the 
forced air 30 to receive the forced air 30. The open end was located at 
the entrance 50A to the plenum 29 and about one inch from the housing 61 
out of the turbulence from the blower 49 and the brackets (not shown) that 
support the blower motor 51. 
With the end of the pitot tube 100 fixed in the housing 61 in a proper 
location and position for accurate measurement of the pressure (dynamic 
and static) at the entrance 50A to the plenum 29, tertiary draft 45 was 
provided first by allowing air to leak into the closed duct 27 where it 
joins the exhaust outlet (or top) 84 of the combustion chamber 21. Interim 
testing indicated that such tertiary combustion draft 45 was necessary. 
Then, as modification 16B, the ports 92C were made in the inclined section 
98 of the bottom 93 of the lower section 65 of the heat exchanger 23. The 
inclined baffle 97C was secured to the inclined section 98 to cover the 
ports 92C and block the forced air 30. 
Finally, instead of the ports 92C in the inclined section 98 and the 
inclined baffle 97C, eight of the ports 92A were provided in the bottom 93 
and the tertiary baffle 97B (shown in FIG. 12B) Was provided as 
modification 16C. 
The unit with the above-described modifications from steps 1-15 the secured 
pitot tube 100 and the eight ports 92A is referred to as Modified Heater 
IV in FIG. 11B. 
Step 17--Test at blocked inlet--reduced rate 
Test Result: pass 
Step 18--Test at blocked inlet--increased rate 
Test Result: fail 
Modifications 
18A--Removed baffle 97B. 
18B--Added three more tertiary ports 92A. 
Meeting the CO Standard after making modifications 18A and 18B indicated 
that even more tertiary combustion draft 45 was required under the extreme 
conditions of steps 11, 12, 15 and 18. Further, the complexity of meeting 
the CO Standard is indicated by the unexpected need to further modify the 
Modified Heater III even though step 12 previously resulted in meeting the 
same test that was later unsuccessfully performed in step 18. 
The unit, modified according to step 18, is referred to in FIG. 11B as line 
"Modified Heater V". 
Step 19--Test at blocked inlet--increased rate 
Test Result: pass 
Step 20--Test at blocked outlet--normal rate 
Test Result: pass 
"Blocked outlet" refers to sequentially decreasing the effective area of 
the heated air outlet 44. If the strip method is used, the method is as 
described with respect to step 9. 
Step 21--Test at blocked outlet--reduced rate 
Test Result: pass 
Step 22--Test at blocked outlet--increased rate 
Test Result: fail 
Modification 
22--Lower the upper temperature limit at which the thermal sensor 54 opens 
the switch 55. Replaced 190.degree. F. thermal sensor 54 with 170.degree. 
F. thermal sensor. 
Investigation by Applicants indicated that the blocked outlet reduced the 
rate of fresh air flow in the fresh air path 67 and through the heated air 
outlet 70. The air in the fresh air path 67 of course receives heat from 
the heat exchanger 23 in proportion to the flow rate in the fresh air path 
67. The reduced fresh air flow rate resulted in a higher operating 
temperature of the heat exchanger 23, which could become unacceptably 
high. 
The modification in step 22 reduced (to a sensed temperature of 170.degree. 
F.) the upper temperature limit at which the burner 36 is shut off. With 
this modification, the Model 1690 was fully modified according to the 
present invention and became the heater 20. 
The following steps indicate that the heater 20 complies with the ANSI 
Standard, including the CO Standard. 
Step 23--Test at blocked outlet--increased rate 
Test Result: pass 
Step 24--Test at normal input rate 
Test Result: pass 
Step 25--Test at reduced rate 
Test Result: pass 
Step 26--Test at increased rate 
Test Result: pass 
Step 27--Test at reduced voltage 
Test Result: pass 
Step 28--Test at increased voltage 
Test Result: pass 
Step 29--Test at blocked inlet--reduced rate 
Test Result: pass 
Step 30--Test at blocked inlet--increased rate 
Test Result: pass 
Step 31--Test at blocked inlet--increased rate 
Test Result: pass 
In summary, Chart 2 below compares the features of the Model 1690 (with the 
Model 1325B) to the heater 20. 
CHART 2 
______________________________________ 
Model 1690 with 
Feature Model 1325B Heater 20 
______________________________________ 
Area of primary 
nominally 0.3066 
0.241 
combustion air 
(0.07 in. .times. 4.38) 
(0.055 .times. 4.38 in) 
inlet 34 (vari- (fixed) 
able) (sq. in.) 
Area of secondary 
0.196 .306 
combustion air 
(4 holes @ (4 holes @ 
inlets 38 (sq. 
.25 dia. each) 
5/16" dia. each) 
in.) 
Area of tertiary 
Zero 0.135 
combustion air (eleven 0.125 
inlets (sq. in.) dia. ports 92A) 
Upper temperature 
190 170 
limit (.degree.F.) read 
by thermal sensor 
54 
Baffle covers 
None Yes 
primary inlets 34 
Baffle covers 1/2 
None Yes 
of secondary 
inlets 38 
Normal supply 
115 120 
voltage 52 (VAC) 
Nominal air pres- 
1.05 (appx.) 0.9 (appx.) 
sure (entrance 
50A to plenum 
29 - inches of 
water) 
Area of heated 
18.19 19.63 
air outlet 44 
(square inches) 
Rating of heater 
52,000 45,000 
(BTU) 
Burner orifice 
#56 (5) #59 (5) 
size and (number 
of orifices) 
CO in combustion 
Less than 0.08% 
Less than 0.08% 
products emitted 
CO air-free. CO air-free 
from exhaust 
stack 64 at 
normal conditions 
(115 VAC, normal 
fuel rate, normal 
voltage 52, no 
blockage of fresh 
air inlet 59 or 
hot air outlet 
44). 
Manifold pressure 
10 10 
at normal input 
rate, (inches of 
water) 
Compliance with 
None Yes, in all tests 
CO Standard per CO Standard 
Air pressure at 
0.2 0.55 
which pressure 
sensor 50 closes 
swith 53A 
(inches of water) 
______________________________________ 
OPERATION OF HEATER 20 
Before initiating operation, the heater 20 is placed at a location that 
requires a supply of heated air, or other suitable place if the flexible 
duct 101 (FIG. 3) is used to guide the heated air to a work location. The 
primary air inlet 34 and the heated air 70 outlet 44 are checked and 
cleared of any debris (not shown). The fuel supply components 80A (FIG. 2) 
are connected to a propane tank (not shown) and the tank output pressure 
is adjusted to between 5 and 50 psi. The heater 20 is plugged into an 
electrical supply (not shown) to supply the voltage 52. This starts the 
motor 51 operating and the blower 49 causes the forced air 30 to flow in 
the paths 66 and 67. To initiate the heating operation of the heater 20, 
the switch 63 is set to the "on" position. The blower 49 causes the forced 
air 30 to flow and the natural draft 35 flows into the primary air inlet 
34, natural and forced drafts 40 into the secondary inlets 38 and the 
natural drafts 45 into the tertiary inlets 42. The forced air 30 at the 
entrance 50A to the plenum 29 increases the air pressure to the minimum 
required for closure of the pressure switch 53A (0.55 inches of water for 
the heater 20) which closes a circuit 102 (FIG. 13) to the controller 56. 
This energizes the fuel valve 57, which opens to supply the propane 46 to 
the burner 36. With these conditions, and normal input rate, the 
controller 56 will energize the igniter 88 and open the fuel valve 57. The 
propane 46 is supplied to the burner orifices 82 and ignites, producing 
the flames 26 and the products of combustion 53. The combustion of the 
propane 46 is supported by (1) the natural combustion draft 35 flowing 
through the primary air inlet 34, (2) the forced and natural secondary 
combustion drafts 40 flowing through the secondary inlets 38, and (3) the 
natural tertiary drafts 45 flowing through the tertiary inlets 42. The 
baffle 33 is effective to fully block the forced air 30 flowing toward the 
primary air inlet 34 and to partially block the forced air 30 flowing 
toward the secondary air inlets 38. 
The products of combustion 53 rise and flow through the inlet 22, through 
the closed duct 27 of the heat exchanger 23 and through the exhaust stacks 
64. The heat exchanger 23 is heated by the combustion products 53, and it 
in turn heats the air in the path 67 so that the heated air exits the 
outlet 44. 
This is the normal operation of the heater 20 that has been shown to 
produce the products of combustion 53 that meet the CO Standard. The 
heater 20 will continue to operate meeting the CO Standard even though the 
input rate drops to 85% of the normal input rate or increases to 112% of 
the normal input rate. This has been described above as the respective 
"decreased rate" or "increased rate." 
Further, the heater 20 will operate and produce the products of combustion 
53 that meet the CO Standard even if the voltage 52 supplied to the heater 
20 drops to 85% of nominal (102 VAC) or increases to 110% of nominal (132 
VAC). 
The fresh air inlet 59 or the heated air outlet 44 may become partially 
blocked and an uncontrolled situation may simultaneously occur within the 
predetermined range of the input rate described above, but the CO Standard 
will be met. 
On the other hand, the heater 20 must shut off in the event that the heated 
air outlet 44 becomes excessively blocked causing the temperature sensed 
by the thermal sensor 54 in the housing 61 to increase above the 
170.degree. F. limit. The thermal sensor 54 senses such over-limit air 
temperature and opens the second switch 55 causing the circuit 102 to open 
and deenergize the fuel valve 57 so that it closes to turn off the burner 
36. 
Similarly, if the fresh air inlet 59 is excessively blocked, the pressure 
at the entrance 50A to the plenum 29 will drop below the low pressure set 
point and the pressure sensor 50 will open the switch 53A, which also 
opens the circuit 102 and deenergizes the fuel valve 57 so that it closes 
and turns the burner 36 off. 
The burner 36 is also turned off if the supply voltage 52 decreases below 
the predetermined range, because this will cause the pressure at the 
entrance 50A of the plenum 29 (sensed by the sensor 50) to decrease below 
the low pressure set point, resulting in burner shut off in a similar 
manner. 
Similarly, an input rate decrease below 85% or increase above 112% of 
normal input rate may cause the burner 36 to shut off, as follows. As to 
excessively low input rate, the flames 26 could extinguish or become too 
small and the flame sensor 89 will cause the burner 36 to shut off. As to 
excessively high input rate, the thermal sensor 54 could sense a 
temperature above the upper limit of 170.degree. F. which would cause the 
burner 36 to shut off. 
The second embodiment of the heater 20, shown in FIG. 3 as the heater 20B, 
also meets the CO Standard for the heater 20B. The temperature limit for 
the thermal sensor 54 was set at 120.degree. F. Otherwise, the data in 
Chart 2 applies to the second embodiment 20B. 
While the preferred embodiments have been described in order to illustrate 
the fundamental relationships of the present invention, it should be 
understood that numerous variations and modifications may be made to these 
embodiments without departing from the teachings and concepts of the 
present invention. Accordingly, it should be clearly understood that the 
form of the present invention described above and shown in the 
accompanying drawings is illustrative only and is not intended to limit 
the scope of the invention to less than that described in the following 
claims.