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.
Duct size for 1000 cfm.
A good rule of thumb for estimating duct diameter and cfm requirements is.
646 3 28 0 16.
Air volume equivalent round air volume cfm 4 6 8 10 12 duct inches cfm 50 6 x 4 550 75 6 x 4 675 100 8 x 4 6 x.
As systems increase in efficiency the tolerances of how we have always done it will no longer be adequate.
Table 4 1 supply air duct installation sizes based on 08 inches of pressure drop per 100 ft round duct rectangular duct cfm dia.
100 0 045 4 x 6.
7 to 10 duct 700 to 900 cfm.
For example for a natural draft furnace multiply 100 cmf by 100 to get 10 000.
Wxh wxh wxh wxh wxh wxh wxh wxh 80 8x4 90 8x4 100 6 6x6 7x5 9x4 125 7x6 8x5 10x4 150 8x6 9x5 11x4 175 7 7x7 9x6 11x5 13x4 200 8x8 8x7 9x6 12x5 15x4.
Air flow dynamics duct sizing reference guide supply or return duct size capacity 09 to 10 pressure drop per 100 el.
Cubic feet per minute cfm m 3 s rectangular duct sizes inches mm x mm equivalent diameter round duct sizes d e inches mm velocity in equivalent round duct v ft min m s friction loss inh 2 o 100 ft duct pa 100m x x 80 0 04 3 x 7 4 x 5.
A natural draft furnace produces 100 cmf an induced furnace produces 130 cfm and a condensing furnace produces 150 cmf.
But if the size of your duct matches your ventilation power your kitchen exhaust fan will do its job properly and quietly.
6 to 8 duct 400 to 600 cfm.
Multiply that number by the amount of cubic feet of airflow per minute cfm your type of furnace produces.
Duct system sizes and airflow quick chart created date.
This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications.
1 000 14 14 x 10 18 x 8 12 x 12 1 200 14 16 x 10 24 x 8 14 x 12.
Equipment sizing load blower cfm equipment sizing load btu hour 1 08 x td x acf.