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Rinnai Corporation Hydronic Furnace (37AHB) Manual
Air Distribution Guide
NOTES:
1. Calculations are based on airflow of 50 CFM for each 3 inch diameter flexible leg.
2. Calculations assume system is equipped with a standard add-on evaporative coil and allows for approximately 120 equivalent length of return ducting.
3. MAF – Maximum airflow (CFM).
4. NOL – Number of 3” diameter flexible legs.
5. If a more detailed duct sizing method is required, refer to one or more of the referenced documents or any other industry recognized standard.
LIST OF REFERENCES:
ACCA - Manual D (Residential Duct Systems)
ACCA - Flexible Duct Performance & Installation Standards
ASHRAE Handbook-Fundamentals
HRAI - Residential Air System Design Manual
SMACNA - HVAC System Duct Design Manual
MAF 140 1 00 75 50
NOL3221
MAF 210 2 00 150 100 50
NOL44321
MAF 320 3 00 250 200 1 50 100 50
NOL6654321
MAF 420 400 350 300 250 200 150 100
NOL88765432
MAF 560 500 450 400 350 300 250 200 150 100
NOL111098765432
MAF 900 8 50 800 750 7 00 650 600 5 50 500 4 50 400 350 3 00 250 200 150
NOL1817161514131211109876543
MAF 1300 1200 1150 110 0 105 0 100 0 950 900 8 50 800 750 7 00 650 6 00 550 500 450 400 350 300 250
NOL2624232221201918171615141312111098765
MAF 1700 1600 1500 140 0 130 0 120 0 110 0 105 0 1000 9 50 900 850 8 00 750 700 650 600 550 500 450 400 350 300
NOL343230282624222120191817161514131211109876
MAF 2300 2200 2100 200 0 190 0 180 0 170 0 160 0 1500 1400 1300 120 0 1 100 1 000 900 850 800 750 700 650 600 550 500 450
NOL4644424038363432302826242220181716151413121110 9
MaximumAirflow(CFM)withMaximumNumberof3"flexlegs
Maximum
Equivalent
DuctLength
(Feet)
Table3:QuickReferenceHi‐VelocityDuctSizingChart
RigidTrunk
DuctDiameter
(inches)
250
120
8 140
100
7
90
6
60
5
4
16 320
200
14
175
12
10