Residential Gas Furnace Operation - HVAC.Amickracing

Determining Natural Gas Furnace Input23140598761 MILLION8710096051234THOUSAND231014059876THOUSAND87196051234THOUSANDHALFTWOF O O TF E E TCUBIC FEET• Measure the time taken for two revolutions of the two cubic foot dial.• Call gas supplier for BTU/Cu.Ft. Heating value of gas– or –• Use 1000 BTU/Cu.Ft. as value(If specific value not available)* Heating value of gas based on sea level pressure.• Calculate Input:Cu.Ft./Hour =Revolutions x Cu.Ft./Revolution x 3600Time (In Seconds)BTUH = Cu.Ft./Hour x BTU/Cu.Ft.Important:Input should never exceed 100% of rated input.Adjust manifold pressure or change main orifice size if requiredCalculating CFM – Temperature Rise MethodMinimum steady state efficiency – 80%– Use AFUE if over 80%BTUH (out) = BTUH (in) xExample:Efficiency100• BTUH (in) = 80,000• AFUE = 90%• BTUH (out) = 80,000 x .90= 72,000• ∆T = 45°CFM =72,00045 x 1.08= 148133