30
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 140 100 75 50
NOL3221
MAF 210 200 150 100 50
NOL44321
MAF 320 300 250 200 150 100 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 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150
NOL1817161514131211109876543
MAF 1300 1200 1150 1100 1050 1000 950 900 850 800 750 700 650 600 550 500 450 400 350 300 250
NOL2624232221201918171615141312111098765
MAF 1700 1600 1500 1400 1300 1200 1100 1050 1000 950 900 850 800 750 700 650 600 550 500 450 400 350 300
NOL343230282624222120191817161514131211109876
MAF 2300 2200 2100 2000 1900 1800 1700 1600 1500 1400 1300 1200 1100 1000 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
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