What is the correct size for a return air vent opening if I'm using a 4-ton 13SEER A/C?

Thanks!

Jeff

Use a duct O later or other sizing tool for the calculations. Usually you will have more than one return air in a house and you also have to deduct to grill cover from the duct size to assure yourself of enough square inches of duct opening. That is why I do not do generic sizes as you requested.

Basically, the bigger it is, the less noise it makes. The air taken in will be the same regardless of how big you make it.

Just don't make it too small otherwise it will make a hissing noise.