Appliance Installation & Clearances
Rating plates, BTU sizing, clearances to combustibles, gas trains, manifolds, burner components, and piping schematics.
- Read and interpret appliance rating plates for BTU input, manifold pressure, and orifice data
- Determine clearances to combustibles from code tables
- Identify gas train components and their sequence
- Explain atmospheric burner operation and primary air adjustment
- Describe orifice sizing differences between natural gas and propane
Leçon 1
Rating Plates & BTU Sizing
Reading the Rating Plate
Every gas appliance has a rating plate (also called a nameplate or data plate) containing critical installation and service information. A gasfitter must be able to read and interpret this data accurately.
Key rating plate information includes:
- BTU input - total gas consumption per hour
- BTU output - useful heat delivered per hour
- Manifold pressure - required gas pressure at the valve
- Orifice size - drill number or size for the gas type
- Gas type - natural gas or propane
- Minimum clearances - distances to combustible materials
- Electrical requirements - voltage, amperage, frequency
- Model and serial number - for parts ordering and recalls
BTU Sizing
Proper sizing ensures the appliance meets the building's heating demand without oversizing (short cycling) or undersizing (insufficient heat). The calculation considers:
- Heat loss of the building (insulation, windows, climate zone)
- Altitude derating - reduce BTU by 4% for every 1,000 feet above sea level
- Appliance efficiency - output = input x efficiency
Altitude Derating
Gas appliances must be derated 4% per 1,000 feet above sea level because the air contains less oxygen at higher altitudes. A 100,000 BTU furnace at 5,000 feet altitude has an effective output of 80,000 BTU.
The rating plate is the primary source of installation data. BTU input is total consumption; output is useful heat. Appliances must be derated 4% per 1,000 feet of altitude above sea level.