Return Air Duct Size Chart

For the same 2 5 ton system with a filter grille the grille size would need to be what size asked rick we usually use a 20 x 20 for 2 5 ton said the tech 20 x 20 x 2 800 800 cfm well that s big enough for a 2 ton but a 20 x 25 may be a better choice.

Return air duct size chart. Since all flexible ducts are not alike use the flexible duct manufacturer s air friction loss data to size the ducts whenever possible. In this instance the 800 cfm divided by 4 000 ft min calls for a duct area of 0 2 sq feet. The less time the cool air is in the hot attic the less heat gain.

Use the air friction chart. In order to maintain velocity reduce duct size. Remember statistically speaking the bottleneck on high static pressure systems is on the return side.

Tees split but do not reduce and an appropriate reducer must be added. The 6 inch diameter duct area is 3 3 3 14 rad x rad x pi 28 3 sq inches which meets the need. Use the minimum length of flexible duct.

Do not use data for round sheet metal duct. Now you have all the information you need to make an educated decision in purchasing your dust collector. If no data is available use the generic flexible duct friction loss chart in acca manual d.

We ll save that calculation for another. 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. 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.

A typical air conditioner heat pump or furnace easily moves 20 tons of air a day. In ductwork the law of conservation of mass means a duct size can be recalculated for a new air velocity using the simple equation. Never locate ducts at the end of the trunk line run.

We pull many pounds of it into our lungs each day. Return air cfm must be equal or greater than supply air cfm. 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.

Yes i m talking about 40 000 pounds. 0 2 sq ft x 144 sq in sq ft 28 8 sq inches cross sectional area of duct. We live in this invisible stuff called air.

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. 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. Dampers on take off duct runs allow for adjustments of air distribution.

Note also the return air grille sizing formula at the top of the chart.