Return Air Duct Size Chart

In ductwork the law of conservation of mass means a duct size can be recalculated for a new air velocity using the simple equation.

Return air duct size chart. We pull many pounds of it into our lungs each day. If clean air return duct is required duct resistance should also be calculated. 0 2 sq ft x 144 sq in sq ft 28 8 sq inches cross sectional area of duct.

In most cases the air in a duct is assumed to be incompressible an assumption that overlooks the change of air density that occurs as a result of pressure loss and flow in the ductwork. In this instance the 800 cfm divided by 4 000 ft min calls for a duct area of 0 2 sq feet. Most people don t know that simply closing a door in their home can make them sick increase their energy bills or reduce their comfort.

We live in this invisible stuff called air. Now you have all the information you need to make an educated decision in purchasing your dust collector. Return air cfm must be equal or greater than supply air cfm.

Use the minimum length of flexible duct. Yes i m talking about 40 000 pounds. Dampers on take off duct runs allow for adjustments of air distribution.

This can be caused by undersized returns long return duct lengths with bends or sound attenuating loops or a poor choice of air filtration. Do not use data for round sheet metal duct. Use the air friction chart.

Note also the return air grille sizing formula at the top of the chart. Our current duct work is 5 in we live in an older house probably only had heat at the time he wants to upgrade to 8 inch duct work upgrade to a 3 5 ton 13 ser increase the size of our return air thing and add a register to our large living room. Since the early 1970 s a significant increase in the use of flexible duct which generally is internally lined with plastic or some other type of material has occurred.

Since all flexible ducts are not alike use the flexible duct manufacturer s air friction loss data to size the ducts whenever possible. Never locate ducts at the end of the trunk line run. Remember statistically speaking the bottleneck on high static pressure systems is on the return side.

A typical air conditioner heat pump or furnace easily moves 20 tons of air a day. You have determined the velocity cfm static pressure and the size of the ductwork. However many modern residential air duct systems are constructed of fiber glass duct board or sheet metal ducts that are lined on the inside with fiber glass duct liner.

Tees split but do not reduce and an appropriate reducer must be added. In order to maintain velocity reduce duct size. We ll save that calculation for another.

The 6 inch diameter duct area is 3 3 3 14 rad x rad x pi 28 3 sq inches which meets the need.