Hvac Duct Fittings Equivalent Length Chart

Q air volume flow cfm cubic feet per minute.

Hvac duct fittings equivalent length chart.

One method of duct design relies on calculating the total effective length which is the sum of all the lengths of the straight sections of duct and the equivalent lengths of the fittings. D e equivalent duct diameter inches. 1 psi equals 27 7 inches of water gauge. Fittings such as elbows tees and valves represent a significant component of the pressure loss in most pipe systems.

This value is the comparison length of this fitting to an equivalent length of straight pipe or duct. Energy vanguard this duct design shows the layout of a duct system including the fittings and duct sizes. The major loss or friction loss in a circular duct in galvanized steel with turbulent flow can for imperial units be expressed. 12 x 7 flat oval 1000 cfm solution.

The strength of the equivalent length method is that it is very simple to calculate. Back of calculator has equivalent feet of straight duct for commonly used fittings corrected pressure drop chart and many hvac formulas. A common duct pressure of 0 25 inches water column is equal to 0 25 divided by 27 7 in wc psi 0 009. A 1 3 1 round duct size and area.

From table a 3 the equivalent round size is 9 4 inches. δh 0 109136 q 1 9 d e 5 02 1. Pull out slide has recommended duct velocities recommended gauges for sheet metal and much more. The weakness of the equivalent length method is that.

δh friction or head loss inches water gauge 100 ft of duct. A 8 2 ashrae duct fitting database program. For example each elbow used is equivalent to 30 feet of straight pipe or duct. Each fitting has an effective length that equates its pressure drop to an equivalent amount of straight duct.

Equivalent duct sizes for same friction loss from. A 9 1 hvac systems duct design sheet metal and air conditioning contractors national association smacna 1990 chantilly va. Southwark metal mfg s sheet metal pipe ductwork and fittings conform to this system of equivalent lengths as well as conforming to industry national standards for describing residential fittings. Use the friction chart at 1000 cfm in 9 4 inch diameter to friction loss is 0 5 in water 100 ft.

This article details the calculation of pressure losses through pipe fittings and some minor equipment using the equivalent length method. For rectangular ducts the equivalent diameter must be calculated.