Duct Sizes For Hvac Ducting

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

Duct sizes for hvac ducting.

One six inch round duct is good for about 120 cfm a six inch duct carries about 150 cfm and eight inch carries about 200 cfm of cool air. Also you want to make sure that the return ducts are the same size as the supply ducts. Run the correct size from the furnace and be sure they are installed correctly. Divide that number by 10 000 btus.

Duct sizing how to size ductwork. Never locate ducts at the end of the trunk line run. The duct size must adequately handle air flow intake and return in order for an hvac system to operate at optimal levels. 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 order to maintain velocity reduce duct size. Installing the duct incorrectly will affect the heating capacity of the system as much as improper sizing. Ducts that are too large will decrease the air flow velocity thereby allowing air to cool or warm before it reaches the registers. Flex duct 05 on most metal duct calculator round metal pipe 06 on most metal duct calculators field duct sizing chart rectangular sheet metal duct 07 on most metal duct calculators.

Use insulated duct or duct board in unheated spaces. As systems increase in efficiency the tolerances of how we have always done it will no longer be adequate. Last take off run to be located 12 18 from end. How to determine duct size per room.

These charts hold a lot of information. If you don t have one you can find them in the following links. Once all the rooms are considered for duct size calculations increase the duct size accordingly. Flexible duct work must be stretched tightly for maximum air flow.

So if you have a two ton system you need ductwork that will carry 800 cfm. Multiply that number by the amount of cubic feet of airflow per minute cfm your type of furnace. Some houses have ducts that are too large or too small. You can obtain these from ductwork manufacturers or from industry bodies such as cibse and ashrae.

Install the appropriate duct size connections. V 2 v 1 a 1 a 2. For example if your furnace. Always stagger take off ducts by 12 to maintain pressure.

For this reason homeowners may want to contact a certified hvac technician or contractor to determine the optimal size of ductwork throughout the home or business environment that also measures up to code standards. To size the ducts you re going to need a duct sizing chart. Link 1 and link 2.