Lennox MPGA 075 B3, MPGA 050 B3, MPGA 075 B4, MPGA 125 B5, MPGA 100 B5 Application Manual

APPLICATION
GUIDE

GAS FURNACE

Fit’s All 80

English/02-2004

UPFLOW, DOWNFLOW OR HORIZONTAL GAS-FIRED

TABLE OF CONTENTS

AFFIX LABEL HERE

INSTALLATION AND SERVICING INSTRUCTIONS

NON-CONDENSING

WARM AIR FURNACE

Issue 0240

Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Furnace Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Location/Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Air for Combustion & Ventilation . . . . . . . . . . . . . . . . . . . . . . . . 8

Ducting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Venting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Electrical Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

RETAIN THESE INSTRUCTIONS FOR FUTURE REFERENCE

Gas Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Start-Up Operation & Checkout . . . . . . . . . . . . . . . . . . . . . . . . . 18

Sequence of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Servicing The Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Trouble Shooting Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Wiring Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Do not store or use gasoline or other
flammable vapors and liquids in the

WHAT TO DO IF YOU SMELL GAS:

vicinity of this or any other appliance.

• Do not try to light any appliance.

Installation and service must be performed
by a qualified installer, service agency or
the gas supplier. Installation by an
unqualified person may lead to equipment
damage and/or a hazardous condition
which may cause bodily injury and harm
and, as such, at the sole discretion of the
manufacturer, the entire warranty may be

• Extinguish any open flame.

• Do not touch any electrical switch; do

not use any phone in your building.

• Immediately call your gas supplier from

a neighbor's phone. Follow the gas
supplier's instructions.

• If you cannot reach your gas supplier,

call the fire department.

voided and be of no further force and
effect.

20541501 Issue 240 Page 1 of 26

SAFETY

The following is a list of safety precautions and their locations in this manual.

These safety rules and precautions must be followed when installing this furnace.

1. Use only with type of gas approved for this furnace. Refer to the furnace rating
plate.

2. Install this furnace only in a location and position as specified in The

Location/Placement Section on page 6 of these instructions.

3. Provide adequate combustion and ventilation air to the furnace space as
specified in Air for Combustion and Ventilation section on page 8 of these
instructions.

4. Combustion products must be discharged outdoors. Connect this furnace to an
approved vent system only, as specified in Venting on page 12 of these
instructions.

5. Never test for gas leaks with an open flame. Use a commercially available
soap solution made specifically for the detection of leaks to check all
connections, as specified in The Gas Connection section on page 16 of these
instructions.

6. Always install furnace to operate within the furnace's intended temperature-rise
range with a duct system which has an external static pressure within the
allowable range, as specified in Furnace Specifications on page 3 of these
instructions. See furnace rating plate.

7. When a furnace is installed so that supply ducts carry air circulated by the
furnace to areas outside the space containing the furnace, the return air shall
also be handled by duct(s) sealed to the furnace casing and terminating outside
the space containing the furnace. See page 11 for Ducting.

8. A gas-fired furnace for installation in a residential garage must be installed as
specified in The Location / Placement section on page 7 of these instructions.

9. The furnace is not to be used for temporary heating of buildings or structures
under construction. As noted on page 6 under Introduction.

20541501 Issue 0240 Page 2 of 26

FURNACE BLOWER SPECIFICATIONS AND AIR FLOW DATA

BLOWER

SYSTEM

MPGA050B3

(10X6 WHEEL)

(1/3HP MOTOR)

MPGA075B3

(10X6 WHEEL)

(1/3HP MOTOR)

MPGA075B4

(12X9 WHEEL)

(1 HP MOTOR)

MPGA100B4

(10X9 WHEEL)

(1 HP MOTOR)

MPGA100B5

(12X9 WHEEL)

(1 HP MOTOR)

BLOWER

SPEED

EXTERNAL STATIC (IN. W.C.)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

MPGA125B5

(12X12 WHEEL)

(1 HP MOTOR)

NOTES:

1. Air flow values in cubic feet per minute (CFM).

2. Data taken without filters in place or A/C evaporator in place.

When operating the furnace in the heating mode, the static pressure and the temperature rise (supply air temperature
minus return air temperature) must be within those limits specified on the rating label. Failure to follow this warning
could lead to severe furnace damage.

Turn OFF all gas and electrical power to furnace before performing any maintenance or service on unit. (Unless
specific test requires gas and electrical supplies.) Failure to take this precaution may result in personal injury due
to electrical shock or uncontrolled gas leakage.

20541501 Issue 0240 Page 4 of 26

FURNACE WIRING SPECIFICATIONS

20541501 Issue 0240 Page 5 of 26

The furnace cabinet must have an uninterrupted or unbroken electrical ground to minimize personal injury if an
electrical fault should occur. The unit must also be electrically grounded in accordance with local codes, or in the
absence of local codes, with the latest edition of the (U.S.) National Electrical Code ANSI/NFPA No. 70 or CSA
Standard C22.1; Part 1 Canadian Electrical Code, if an external electrical source is utilized. DO NOT use gas piping
as an electrical ground.

INTRODUCTION

This furnace is design certified by CSA International as a Category I furnace using air from inside the structure for

combustion.

It is shipped as a packaged unit, complete with burners and controls, and requires a line voltage (115V) connection to

the junction box, a thermostat hook-up as per the wiring diagram and a gas line connection. This furnace can be installed

in either upflow, downflow or horizontal airflow positions. The design of this furnace is NOT CSA Certified for
installation in recreation vehicles, in manufactured (mobil) homes, outdoors or for temporary construction heating.

This furnace has been designed to interface with split system cooling equipment (approved by a nationally recognized
testing laboratory) so as to provide "year round air conditioning". The blower has been sized for both heating and cooling
and the furnace controls include a cooling fan relay.

The furnace installation must conform with local building codes or in the absence of local codes, with the latest edition
of the (U.S.) National Fuel Gas Code ANSI Z223.1 (NFPA-54) or Canadian Natural Gas and Propane Installation Codes
CSA B149.1.

For complete information on installation standards consult the (U.S.) National Fuel Gas Code, obtainable from the
National Fire Protection Association, Inc., Batterymarch Park, Quincy, MA 02269 or the American Gas Association, 1515
Wilson Boulevard Arlington, VA 22209 or the Canadian installation codes obtainable from Canadian Standards Association,
178 Rexdale Boulevard, Etobicoke, Ontario, Canada M9W 1R3.

This furnace is designed for minimum continuous return-air temperature of 60°F dB or intermittent operation down to
55°F dB such as when used with a night setback thermostat. Return-air must not exceed a maximum continuous
temperature of 85°F dB.

These instructions are written for individual residential installation only. For multi-unit installation or
commercial applications, please contact manufacturer for recommendations.

LOCATION / PLACEMENT

Site Selection: This furnace may be located in an attic, closet, basement, crawl space, alcove or suspended from the

ceiling of a utility room or basement. Select a location that will meet all requirements for safety,
clearances, ventilation and combustion air, ductwork design, gas piping, electrical wiring and venting.

Clearances: The following minimum clearances, or greater, must be provided between the furnace and adjacent

construction.

TABLE 1 MINIMUM INSTALLATION CLEARANCES

"UPFLOW" POSITION "DOWNFLOW" POSITION "HORIZONTAL" POSITION

Suitable for alcove or closet
installation† on combustible
flooring at minimum
clearance from adjacent
construction not less than
the following:

Top Sides Back Front Vent

2" 1" 1" 6" 6" with single wall vent
2" 1" 1" 3" 1" with B1 vent

† For closet installation see Air for Combustion and Ventilation.

Suitable for alcove or closet installation† on non­combustible flooring at minimum clearance from
adjacent construction not less than the following:
* Installation on combustible flooring only when
installed on special base (see model & rating label
for proper special base).

Suitable for attic, alcove or closet installation† on
combustible flooring at minimum clearance from
adjacent construction not less than the following:
* Line contact only permissible between lines
formed by intersection of the top and two sides of
the furnace jacket and building joist, studs, or
framing.

20541501 Issue 0240 Page 6 of 26

Failure to comply with all of the clearances will
create a fire hazard.

The furnace should also be located as near to the
center of the air distribution system as possible, and
should be installed level.

This furnace may be installed on non-combustible
flooring or on wood flooring, however, it must not be
installed directly on carpeting, tile or any other
combustible material. In the downflow position, it must
be installed on non-combustible flooring or on the special
base listed on the rating label.

In a horizontal position, line contact is only
permissible between lines formed by the intersection of
the furnace top, the front and back sides, and building
joists, studs or framing (See Figure 1).

Figure 1

HORIZONTAL LINE CONTACT

Do not place combustible material on the furnace
jacket. Failure to comply with this warning will
create a fire hazard.

This furnace is not watertight and is not designed
for outdoor installation. This furnace shall be
installed in such a manner as to protect the
electrical components from water. Outdoor
installation would lead to a hazardous electrical
condition and to premature furnace failure.

Furnace must not lean back. It must be level or
tilt up to 2° to the front. (See Figure 1.)

A clearance of at least 30" should be provided at the
front of the unit for servicing. For attic installations, the
passageway and servicing area adjacent to the furnace
should be floored.

If the furnace is to be installed in a crawl space,
consult local codes. (Use of a concrete pad 1" to 2" thick
is recommended.)

If the furnace is to be suspended from the ceiling, it
will be necessary to use steel pipe straps around each
end of the furnace. These straps should be attached to
the furnace with sheet metal screws and to the rafters
with bolts. The furnace may also be suspended by using
an angle iron frame bolted to the rafters. (See Table on
page 3 for size and weight of furnace.) Care must be
taken to allow for service access.

If a furnace is to be installed in a residential garage,
it must be installed so the burners and the ignition source
are located not less than 18" above the floor and the
furnace must be located or protected to avoid physical
damage by vehicles.

20541501 Issue 0240 Page 7 of 26

AIR FOR COMBUSTION AND VENTILATION

Contaminated Combustion Air:

This furnace is not to be installed in a structure
defined as having contaminated combustion air. Allowing
exposure to substances containing chlorine or fluoride
could harm the furnace and void the warranty.
Substances to avoid include, but are not limited to:

• Permanent wave solutions

• Chlorinated waxes and cleaners

• Chlorine based swimming pool chemicals

• Water softening chemicals

• De-icing salts or chemical

• Carbon tetrachloride

• Halogen type refrigerants

• Cleaning solvents (such as perchloroethylene)

• Printing inks, paint removers, varnishes, etc.

• Hydrochloric acid

• Cements and glues

• Antistatic fabric softeners for clothes dryers

• Masonry acid washing materials

• Unrefined gases

Contaminated combustion air may cause premature
failure of the heat exchanger that may lead to a
hazardous condition and/or bodily harm, or loss of
life.

Adequate Ventilation and Combustion Air:

This section is provided to give guidelines for the
introduction of air for ventilation and combustion air. The
total quantity of air provided to the installation area must
equal the requirements of all gas appliances in the area.

Adequate facilities for providing air for combustion
and ventilation must be provided in accordance with the
latest edition of the National Fuel Gas Code ANSI
Z223.1/NFPA54 or CSA B149.1 Natural Gas and Propane
Installation Codes, or applicable provisions of the local
building codes.

The furnace shall be installed in a location in which
the facilities for ventilation permits satisfactory combustion
of gas, proper venting and maintenance of ambient
temperature at safe limits under normal conditions of use.
The furnace shall be located so as not to interfere with
proper circulation of air.

In addition to air needed for combustion, ventilation in
the form of process air must be provided as required for:
cooling of equipment or material, controlling dew point,
heating, drying, oxidation or dilution, safety exhaust and
odor control. Air must be supplied for ventilation,
including all air required for comfort and proper working
conditions for personnel.

For purposes of this instruction the following

definitions apply:

Confined Space: A space whose volume is less

than 50 cubic feet per 1000
Btu/hr of the aggregate input
rating of all appliances installed
in that space.

Unconfined Space: A space whose volume is not

less than 50 cubic feet per 1000
Btu/hr of the aggregate input
rating of all appliances installed
in that space. Rooms
communicating directly with the
space in which the appliances
are installed, through openings
not furnished with doors, are
considered a part of the
unconfined space.

If the installation area meets the definition of
"Unconfined Space" and does not have additional air
requirements as described, the furnace may be installed
without making special provisions for combustion and
ventilation air.

Whenever this furnace is installed in an area along
with one or more gas appliances, the total Btu/hr
input of all appliances must be included when
determining the free area requirements for
combustion and ventilation air openings.

Do not block the combustion or ventilation air
openings in the furnace. Any blockage will result in
improper combustion and may result in a fire
hazard or unsafe condition.

20541501 Issue 0240 Page 8 of 26

If ventilation and/or combustion air must be supplied to the "Confined Space" from inside the building structure, two
permanent openings to an additional room of sufficient volume as to combine the volumes of the spaces to meet the
criteria for an "Unconfined Space" must be created. Each opening must have a free area of not less than one square
inch per 1000 Btu per hour of total input of all appliances within the "Confined Space" (but not less than 100 square
inches). These openings must be located 12 inches from the top and bottom of the furnace area respectively and must
be at least 3 inches long on the smaller side of the opening (See Figure 2). Neither opening can be blocked at any time.

Figure 2 CONFINED SPACE / INDOOR AIR

TOTAL INPUT

(Btuh)

40,000
60,000

80,000
100,000
120,000
140,000
160,000

EXAMPLE:

50,000 Btuh Furnace & 10,000 Btuh Water
Heater = 60,000 Btuh Total Input = 12"
Dia. Round Duct.

MIN. FREE AREA

(Sq. In.)

100
100
100
100
120
140
160

ROUND DUCT

(Dia. In.)

12
12
12
12
13
14
15

If ventilation and/or combustion air must be supplied to the "Confined Space" from outside the building structure,
two permanent openings to the outdoors must be created. Each opening must have a free area of not less than one
square inch per 4000 Btu per hour of total input of all appliances within the "Confined Space". These openings must
be located 12 inches from the top and bottom of the furnace area respectively (See Figures 3, 4, and 5). Neither
opening can be blocked at any time.

Figure 3 CONFINED SPACE / OUTDOOR AIR

20541501 Issue 0240 Page 9 of 26

TOTAL INPUT

(Btuh)

40,000
60,000

80,000
100,000
120,000
140,000
160,000

EXAMPLE:

50,000 Btuh Furnace & 10,000 Btuh Water
Heater = 60,000 Btuh Total Input = 5" Dia.
Round Duct.

MIN. FREE AREA

(Sq. In.)

10
15
20
25
30
35
40

ROUND DUCT

(Dia. In.)

4
5
5
6
6
7
8

Figure 4

Figure 5

CONFINED SPACE / OUTDOOR AIR

FROM ATTIC

CONFINED SPACE / OUTDOOR AIR

FROM ATTIC & CRAWL SPACE

When horizontal ducts are used to supply air from the
outdoors, they must be of the same cross sectional area
as the free area of the openings to which they connect.
The minimum dimension of rectangular air ducts must not
be less than 3 inches. Each opening must have a free
area of not less than one square inch per 2,000 Btu per
hour of total input of all appliances within the "Confined
Space". These openings must be located 12 in. from the
top and bottom of the furnace area. Neither opening can
be blocked at any time (See Figure 6).

Figure 6

CONFINED SPACE / OUTDOOR

AIR THROUGH HORIZONTAL DUCTS

Furnaces installed with combustion air drawn from
a heated space which includes exhaust fans,
fireplaces, or other devices that may produce a
negative pressure should be considered confined
space installations.

For an attic installation it is important to keep
insulation 12" or more away from any furnace
openings. Some types of insulating materials may
be combustible.

20541501 Issue 0240 Page 10 of 26