1. RESIDENTIAL CONDENSING GAS FURNACES Vent Design & Installation Training
Spring 2014
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2. RESIDENTIAL CONDENSING GAS FURNACES Vent Design & Installation Training Contents
Section 1: 35” Condensing Furnace Design
Section 2: National and International Codes
Section 3: Vent Design Considerations
Section 4: Vent Installation
Section 5: Results of Poor Vent Design and Installation
Uses neutral air pressure.
Moves gases, lighter than air
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3. RESIDENTIAL CONDENSING GAS FURNACES
Section 1
35” Condensing Furnace Design
Uses neutral air pressure.
Moves gases, lighter than air
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4. RESIDENTIAL CONDENSING GAS FURNACES Condensation Management Comparison
System Condensate Load
Vent
Legacy 92% New 92% New 98%
high
Flue Gas Temp
low
Vapor
Liquid
Liquid
Vapor
Vapor
Liquid
Drain
Lower flue gas temps More liquid condensate in vent
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5. RESIDENTIAL CONDENSING GAS FURNACES Vent Condensate Load Comparison
Legacy 92% New 92% New 98%
Inducer
Airflow
Vapor
Vapor
Vapor
Liquid
Liquid
Liquid
More liquid in vent Vent pitch is important
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6. (Single & 2-Stage Models)
RESIDENTIAL CONDENSING GAS FURNACES Normal Pressure Switch Operation: Single & 2-Stage
LPS (Low Pressure Switch)
Measures: collector box pressure
Purpose: Prevent furnace operation during restricted heat exchanger, trap or condensate drain
Status Code 3
(Single & 2-Stage Models)
HPS (High Pressure Switch)
Measures: inducer housing pressure
Purpose: Prevent furnace operation during restricted vent
Pressure switches are used to prevent CO from backing up into a structure.
Pressure switches are not for “furnace proving”.
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7. RESIDENTIAL CONDENSING GAS FURNACES
Section 2
National and International Codes
Uses neutral air pressure.
Moves gases, lighter than air
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8. PLUMBING CODES Applicability to Fuel Gas Appliance Venting
National Standard Plumbing Code 2009
International Plumbing Code 2012
NSPC plumbing definition excludes piping for ‘environmental control’.
IPC plumbing definitions excludes fuel gas appliance exhaust or combustion air.
NSPC vent definitions do not refer to fuel gas appliance exhaust.
IPC vent definitions do not include fuel gas appliance exhaust or combustion air.
Fuel gas appliances are regulated by the National or International Fuel Gas Code or International Residential Code.
Uses neutral air pressure.
Moves gases, lighter than air
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9. FUEL GAS CODES Vent, Combustion Air and Make-up Air
NATIONAL FUEL GAS CODE 2012 ANSI Z223.1, NFPA 54
INTERNATIONAL FUEL GAS CODE 2012*
*IFGC applies to residential gas furnaces in 1 or 2 family dwellings and townhouses.
NFGC and IGFC refer to manufacturer’s Installation Instructions/Manual for vent design, sizing and installation.
IFGC refers to manufacturer’s Installation Instructions/Manual for vent support, combustion and ventilation air requirements
Vent and combustion air termination location is specified in NFGC.
Make-up and combustion air is specified in IFGC.
Refer to National and International Fuel Gas Codes and manufacturer’s Installation Instructions/Manual for vent, combustion air, ventilation and make-up air design and installation.
The condensing furnace is a category IV appliance.
Moves gases, lighter than air
Uses neutral air pressure. 9
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10. RESIDENTIAL CONDENSING GAS FURNACES
Section 3
Vent Design Considerations
Uses neutral air pressure.
Moves gases, lighter than air
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11. RESIDENTIAL CONDENSING GAS FURNACES Nuisance HPS Trip Causes: Vent Length
Cause 1: Maximum vent length in Installation Instructions were exceeded.
Cause 2: Smallest practical vent diameter not used.
Affect on Operation: Vent system pressure drop exceeds furnace capacity. Starves burner of combustion air resulting in incomplete combustion.
Affect on Operation: Vent system pressure drop is too low.
Too much combustion air resulting in unstable flame.
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12. RESIDENTIAL CONDENSING GAS FURNACES Nuisance HPS Trip Causes: Vent Termination
Cause: Vent termination/s are below the snow line.
Cause: Combustion air and vent termination/s are located too close to another fuel gas appliance vent, dryer vent and plumbing stack.
Affect on Operation: Vent or combustion intake termination freezes
Affect on Operation: Combustion products are pulled into combustion air intake (recirculation). Burners are starved of oxygen which results in incomplete combustion.
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13. RESIDENTIAL CONDENSING GAS FURNACES Nuisance HPS Trip Causes: Termination Location
Cause: Vent and combustion air termination is not protected from prevailing winds.
Cause: Vent and combustion air termination is located in an inside corner.
Affect on Operation: Inducer is unable to overcome static wind pressure.
Affect on Operation: Combustion products are pulled into combustion air intake (recirculation). Burners are starved of oxygen which results in incomplete combustion.
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14. RESIDENTIAL CONDENSING GAS FURNACES
Section 4
Vent Installation
Uses neutral air pressure.
Moves gases, lighter than air
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15. RESIDENTIAL CONDENSING GAS FURNACES Nuisance HPS Trip Causes: Vent Installation
Cause: Inadequate pipe support resulting in sags.
Cause: Inadequate slope
Affect on Operation: Condensate is accumulates at elbows or horizontal sections and partially blocks flow. Large condensate masses will slug back to the inducer creating a pressure wave.
Affect on Operation: Inducer pressure can start condensate waves in the low section of vent pipe, which varies the static pressure on the inducer.
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16. RESIDENTIAL CONDENSING GAS FURNACES Nuisance HPS Trip Causes: Vent Installation
Horizontal sections less than 4 feet,
Elbow sockets do not allow adequate slope, use 45 elbows
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17. RESIDENTIAL CONDENSING GAS FURNACES
Section 5
Results of Poor Vent Design and Installation
Uses neutral air pressure.
Moves gases, lighter than air
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18. Heat Exchanger Corrosion
RESIDENTIAL CONDENSING GAS FURNACES Results of Poor Vent Design & Installation
Status Code 3, No Heat
Loss of Flame Sense
Heat Exchanger Corrosion
Customer Dissatisfaction
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19. Resources
Uses neutral air pressure.
Moves gases, lighter than air
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20. Air Pressure from Inducer
RESIDENTIAL CONDENSING GAS FURNACES Plumbing vs Condensing Furnace Vent Systems
Plumbing Vent, Stack Pipe
Draws in oxygen for waste digestion
Expels harmful vapors through roof
Plumbing Drain
Flushes liquids & solids
Condensing Furnace Vent
Pulls in combustion air (negative pressure)
Pushes out flue gas (positive pressure)
Moves liquid condensate to furnace
Gravity used to overcome inducer air pressure and condensate surface tension.
Gravity
Surface tension
Air Pressure from Inducer
Uses neutral air pressure.
Moves gases, lighter than air
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21. NATIONAL STANDARD PLUMBING CODE 2009 Definition and Scope for Plumbing
Uses neutral air pressure.
Moves gases, lighter than air
Plumbing definition excludes piping for ‘environmental control’.
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22. NATIONAL STANDARD PLUMBING CODE 2009 Definition and Scope for Vent
Uses neutral air pressure.
Moves gases, lighter than air
No vent definitions refer to fuel gas appliance exhaust.
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23. INTERNATIONAL PLUMBING CODE 2012 Scope of Plumbing Code
Uses neutral air pressure.
Moves gases, lighter than air
Fuel gas appliances are regulated by the International Fuel Gas Code.
Fuel gas appliances in houses are regulated by the International Residential Code.
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24. INTERNATIONAL PLUMBING CODE 2012 Definition of Plumbing
Uses neutral air pressure.
Moves gases, lighter than air
Plumbing definitions do not include fuel gas appliance exhaust or combustion air.
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25. INTERNATIONAL PLUMBING CODE 2012 Definition of Vent
Vent definitions do not include fuel gas appliance exhaust or combustion air.
Uses neutral air pressure.
Moves gases, lighter than air
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26. NATIONAL FUEL GAS CODE 2012 ANSI Z223.1, NFPA 54 Vent Code
Uses neutral air pressure.
Moves gases, lighter than air
Vent and combustion air termination location is specified in NFGC.
NFGC refers to manufacturer’s Installation Instructions/Manual for vent sizing and installation.
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27. INTERNATIONAL FUEL GAS CODE 2012 Scope
Uses neutral air pressure.
Moves gases, lighter than air
Applies to residential gas furnaces in 1 or 2 family dwellings and townhouses.
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28. INTERNATIONAL FUEL GAS CODE 2012 Definition of Direct Vent
Uses neutral air pressure.
Moves gases, lighter than air
The condensing furnace is a category IV appliance.
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29. INTERNATIONAL FUEL GAS CODE 2012 Vent Code
Uses neutral air pressure.
Moves gases, lighter than air
IFGC refers to manufacturer’s Installation Instructions/Manual for vent design, sizing and installation.
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30. INTERNATIONAL FUEL GAS CODE 2012 Definition of Direct Vent
Uses neutral air pressure.
Moves gases, lighter than air
IFGC refers to manufacturer’s Installation Instructions/Manual for vent installation and support requirements.
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31. INTERNATIONAL FUEL GAS CODE 2012 Definition of Direct Vent
Uses neutral air pressure.
Moves gases, lighter than air
IFGC refers to manufacturer’s Installation Instructions/Manual for combustion and ventilation air.
Make-up and combustion air specified in IFGC.
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32. INTERNATIONAL FUEL GAS CODE 2012 Definition of Direct Vent
Uses neutral air pressure.
Moves gases, lighter than air
Vent termination location is specified in International Fuel Gas Code.
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