WW-F-2743A
3.8.2 Efficiency. Unless otherwise specified (see 6.2), the efficiency of type I and type II units at the contractor's rated thermal input shall be not less than the following.
3.8.2.1 Group 1 units. The annual fuel utilization efficiency (AFUE) for group 1 units shall be as certified by the contractor to the Federal Trade Commission (FTC) 10 CFR Part 305, but not less than 80 percent.
3.8.2.2 Group 2 and group 3 units. The steady-state efficiency of oil-fired units shall be not less than 81 percent and not less than 80 percent for gas-fired units. The steady-state efficiency shall be based upon the contractor's rated thermal input as listed or certified under the appropriate standards cited in 3.7.
3.8.3 Output capacity. Unless otherwise specified (see 6.2), the rated output (bonnet) capacity shall be not less than 80 percent of the contractor's rated thermal input as listed or certified under the appropriate standards cited in 3.7. For group 1, type I furnaces, the applicable information may be provided on the fact sheets required by the FTC.
3.8.4 Temperature rise. The nominal air temperature rise between the inlet and outlet connections at the contractor's rated thermal output shall be 85 degrees Fahrenheit ( F) 2 F (29 degrees Celsius ( C) 1 C) or other rise as specified by the manufacturer and shown on the rating name plate (see 6.2). All units shall be capable of being adjusted or regulated to provide not less than a 30 F (- 1 C) range of temperature rise, the lower limit being 15 F (- 9 C) less than the rated temperature rise and without exceeding a temperature 15 F (- 9 C) below high limit cutout of not greater than 200 F (93 C).
3.8.5 Air flow. The air flow at the rated output (bonnet) capacity, in cubic feet per minute (cfm) (cubic metre per second (m3/s)) of air at the blower or fan intake, shall be established in accordance with UL 727, UL 731,UL 795, ANSI Z21.47, or ANSI Z83.8 as applicable. The calculated air flow rate for the specified rated temperature rise 85 F (29 C) shall be attained against the applicable external static pressure (esp) given in the standards, unless an alternate esp or temperature rise is shown on the rating name plate (see 6.2). When an alternate temperature rise and esp are required, the air flow rate shall be established in accordance with the following formula:
Air delivery = input x efficiency
1.08 x temperature rise
where: Air delivery = cfm (m3/s)
Thermal input = manufacturer's rated input Btu/hr (W) (see 3.8.1) Efficiency = 0.80 (not less than)
1.08 = 0.244 x 60
13.5
8
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