Adjusting for burner efficiency: 37.21 divided by 0.95 = 39.17 cubic feet of natural gas consumed in one hour. The energy equation is given by: (1 + f) * ht4 = ht3 + f * nb * Q where ht is the specific total enthalpy, f is the fuel to air mass flow ratio, Q is the heat release, and nb is an efficiency factor. Forced-draft burners use blowers to provide pressurized air to oxidize the fuel and to produce different flame patterns. For a burner that is 95-percent efficient, divide by 0.95. However, if a furnace is rated at 100,000 BTUs and is 92% efficient, then the heat output will be 92,000 BTUs (100,000 × .92). In the burner, heat is released in the combustion process, and the energy equation must be used to determine the temperature change. For example, if a furnace has a listed input rating of 90,000 Btu's and an efficiency rating of 80%, it will produce 90,000 Btu input X .80 efficiency … Combustor/burner or afterburner: , Turbine: Nozzle: , . 6. If the model number of your furnace ends in 115, there's in a good chance that it has an input of 115,000 BTU/h. Adjust for the burner efficiency by dividing consumption at 100 percent efficiency by the burner efficiency rating. What is a BTU? 2 Ideal Assumptions. How many BTU furnace would fit your home perfectly? The performance of a furnace is usually assessed by the following indices. It represents the ratio of annual heat output compared to the consumed fossil fuel energy. Calculation of the Air Requirement for Complete Combustion of Fuel Gases Example 1 Calculate the theoretical air-gas ratio at MSC of a fuel gas manufactured by the ICI 500 process containing (by volume) 14.8% CO 2 2.7% CO 48.9% H 2 33.6% CH 4 3 Ideal Ramjet . Use a Smart Thermostat. If this 1,900-square-foot home is in Washington, D.C., however, and the furnace you’re looking at has an 80 percent efficiency, the input rating should be 100,000 BTUs. 11. Then, to calculate the output on a given gas furnace, multiply it's efficiency rating by it's listed input rating to determine the actual Btu output of heat. Inlet/Diffuser: , (adiabatic, isentropic) Compressor or fan: , . 6. Fortunately, calculating furnace size (be it natural gas, propane, or oil) is not rocket science.. To help future furnace owners out, we have developed a simple furnace sizing calculator. Most homeowners have difficulties figuring out what size of furnace do they need. Thermal Efficiency. To get started with a simple example (no turbomachinery), we will reexamine the ideal ramjet, picking up where we left off in Section 3.7.3. A significant efficiency impact on burners is the ratio mix of the air and fuel. The British Thermal Unit, or BTU, is an energy unit. It is approximately the energy needed to heat one pound of water by 1 degree Fahrenheit. high efficiency gas or oil condensing furnace: 85 - 95 % ; Furnace Performance Indices. 11. μ t = thermal efficiency. 1 BTU = 1,055 joules, 252 calories, 0.293 watt-hour or the energy released by burning one match. In the example: 40,000 BTU divided by 1,075 = 37.21. Furnaces typically have around an 80 percent efficiency rating, although more expensive, high-energy models have at least a 93 percent efficiency rating. E o = energy output (W, Btu/h) E i = fuel energy input (W, Btu/h) Annual Fuel Utilization Efficiency - AFUE 1 watt is approximately 3.412 BTU per hour. μ t = 100 E o / E i (1) where . Parameters for Properly Designed and Operated Flares Report for Flare Review Panel April 2012 Prepared by U.S. EPA Office of Air Quality Planning and Standards (OAQPS) The efficiency of a furnace is measured by the Annual Fuel Utilization Efficiency (AFUE). 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