Page 1
05/09
*2P0509*
505,065M
*P505065M*
E 2005 Lennox Industries Inc.
Dallas, Texas, USA
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
INSTALLATION
INSTRUCTIONS
G51MP SERIES UNITS
GAS UNITS
505,065M
05/2009
Supersedes 07/2007
Table of Contents
Unit Dimensions 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
G51MP Parts Identification 3. . . . . . . . . . . . . . . . . . . . . .
Shipping and Packing List 4. . . . . . . . . . . . . . . . . . . . . .
Safety Information 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Use of Furnace as a Construction Heater 5. . . . . . . . .
General 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Combustion, Dilution & Ventilation Air 6. . . . . . . . . . . .
Installation − Setting Equipment 9. . . . . . . . . . . . . . . . . .
Filters 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Duct System 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pipe & Fittings Specifications 16. . . . . . . . . . . . . . . . . . . .
Vent Piping Guidelines 18. . . . . . . . . . . . . . . . . . . . . . . . .
Joint Cementing Procedure 19. . . . . . . . . . . . . . . . . . . . .
Venting Practices 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Piping 31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical 34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit Start−Up 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Pressure Adjustment 39. . . . . . . . . . . . . . . . . . . . . .
High Altitude Information 41. . . . . . . . . . . . . . . . . . . . . . .
Other Unit Adjustments 43. . . . . . . . . . . . . . . . . . . . . . . . .
Service 46. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Planned Service 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Repair Parts List 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ignition Control Board Diagnostic Codes 52. . . . . . . . . .
Vent Pipe Sizing Worksheet 53. . . . . . . . . . . . . . . . . . . . .
Start−Up & Performance Check List 53. . . . . . . . . . . . . .
WHAT TO DO IF YOU SMELL GAS:
Do not store or use gasoline or other
flammable vapors and liquids in the
vicinity of this or any other ap-
pliance.
Installation and service must be
performed by a qualified installer,
service agency or the gas supplier.
D Do not try to light any appliance.
D Do not touch any electrical switch; do not
use any phone in your building.
D Immediately call your gas supplier from a
neighbor’s phone. Follow the gas supplier’s
instructions.
D If you cannot reach your gas supplier, call
the fire department.
FIRE OR EXPLOSION HAZARD.
Failure to follow safety warnings exact-
ly could result in serious injury, death,
or property damage.
WARNING
D Leave the building immediately.
Litho U.S.A.
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