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 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. Remember statistically speaking the bottleneck on high static pressure systems is on the return side.

This can be caused by undersized returns long return duct lengths with bends or sound attenuating loops or a poor choice of air filtration. 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. We pull many pounds of it into our lungs each day.

You have determined the velocity cfm static pressure and the size of the ductwork. Note also the return air grille sizing formula at the top of the chart. Never locate ducts at the end of the trunk line run.

If clean air return duct is required duct resistance should also be calculated. 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. 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.

A typical air conditioner heat pump or furnace easily moves 20 tons of air a day. Return air cfm must be equal or greater than supply air cfm. Tees split but do not reduce and an appropriate reducer must be added.

Use the minimum length of flexible duct. Dampers on take off duct runs allow for adjustments of air distribution. Use the air friction chart.

Now you have all the information you need to make an educated decision in purchasing your dust collector. Do not use data for round sheet metal duct. 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.

We live in this invisible stuff called air. The less time the cool air is in the hot attic the less heat gain. Yes i m talking about 40 000 pounds.

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. If no data is available use the generic flexible duct friction loss chart in acca manual d. In order to maintain velocity reduce duct size.

Since all flexible ducts are not alike use the flexible duct manufacturer s air friction loss data to size the ducts whenever possible.