Duct Sizes For Hvac Ducting

Installing the duct incorrectly will affect the heating capacity of the system as much as improper sizing.

Duct sizes for hvac ducting.

Last take off run to be located 12 18 from end. 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. Once all the rooms are considered for duct size calculations increase the duct size accordingly. V 2 v 1 a 1 a 2.

Use insulated duct or duct board in unheated spaces. 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. So if you have a two ton system you need ductwork that will carry 800 cfm. Ducts that are too large will decrease the air flow velocity thereby allowing air to cool or warm before it reaches the registers.

Always stagger take off ducts by 12 to maintain pressure. Flexible duct work must be stretched tightly for maximum air flow. To size the ducts you re going to need a duct sizing chart. For instance a 2 5 ton system approximately 400 cfm per ton would require 2 14 flexible return ducts or 1 very short flexible 18 duct to move the 1000 cfm required by the 2 5 ton system.

Multiply that number by the amount of cubic feet of airflow per minute cfm your type of furnace. In ductwork the law of conservation of mass means a duct size can be recalculated for a new air velocity using the simple equation. Install the appropriate duct size connections. Duct sizing how to size ductwork.

As systems increase in efficiency the tolerances of how we have always done it will no longer be adequate. The duct size must adequately handle air flow intake and return in order for an hvac system to operate at optimal levels. Divide that number by 10 000 btus. 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.

Never locate ducts at the end of the trunk line run. Look at the plate on your furnace to figure out how many btus it produces. You can obtain these from ductwork manufacturers or from industry bodies such as cibse and ashrae. 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.

Link 1 and link 2. In order to maintain velocity reduce duct size. How to determine duct size per room. These charts hold a lot of information.

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. To maintain a house s energy efficiency the correct heating duct sizes are crucial.