Correctly calculating the return duct size for your AC unit is very important.
Undersized return air ducts result in the ducts and grills being more noisy than usual and the air conditioner components becoming stressed, thus reducing the lifetime of the unit.
Use our handy return air duct size calculator or charts below to help you determine the correct return air vent size for your home.
These charts and calculators are intended to calculate the return air duct only. You can click here to find our standard duct size calculator.
Return Air Duct Size Calculator
To use this calculator, choose your condensing unit size and you will be given the relevant details.
Return Air Duct Size Chart
| AC Unit Capacity | Round Duct Size | Rectangle Duct Size WxH |
|---|---|---|
| 1.5 Ton | 14” | 13″x12″, 14″x11″, 15″x10″, 17″x9″, 19″x8″, 23″x7″, 28″x6″ |
| 2 Ton | 14” | 14″x13″, 15″x12″, 17″x11″, 18″x10″, 21″x9″, 24″x8″, 28″x7″, 36″x6″ |
| 2.5 Ton | 16” | 15″x14″, 17″x12″, 19″x11″, 21″x10″, 25″x9″, 29″x8″, 37″x7″, 41″x6″ |
| 3 Ton | 18” | 16″x15″, 17″x14″, 20″x12″, 23″x11″, 26″x10″, 29″x9″, 34″x8″, 40″x7″ |
| 3.5 Ton | 19” | 16″x17″, 20″x14″, 23″x12″, 26″x11″, 29″x10″, 32″x9″, 38″x8″, 45″x7″ |
| 4 Ton | 19” | 17″x17″, 19″x16″, 22″x14″, 25″x12″, 28″x11″, 31″x10″, 36″x9″, 43″x8″ |
| 5 Ton | 22” | 19″x19″, 20″x18″, 23″x16″, 25″x15″, 27″x14″, 32″x12″, 41″x10″, 47″x9″ |
Frequently Asked Questions
What return duct size do I need for a 2 Ton unit?
For a 2 ton unit you can use either a 19″ flex duct or one of the following rectangular ducts: 14″x13″, 15″x12″, 17″x11″, 18″x10″, 21″x9″, 24″x8″, 28″x7″, 36″x6″.
What is the Duct Size For a 4 Ton Unit?
For a 4 ton unit you can use either a 14″ flex duct or one of the following rectangular ducts: 17″x17″, 19″x16″, 22″x14″, 25″x12″, 28″x11″, 31″x10″, 36″x9″, 43″x8″.
Should my return duct size be the same size as the supply duct?
A general rule to follow is that the return air duct should always be AT LEAST as big (and preferably bigger) as the supply duct.
What happens if The return air vent is too small?
If the return air duct is too small then it will result in excess noise (possibly whistles), reduced efficiency and a reduced lifespan of your AC system.
Does My Return Air Vent Need a Filter?
Whether or not your return air vents need filters depends on several factors. If your HVAC system has an existing filter, you don’t need a return vent filter, but you can add them if you like.
You can learn more about this in our return air vent filter guide.
