Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

HVAC Calculating Return Air

HVAC Calculating Return Air

HVAC Calculating Return Air

Question: From toolbag
Is there a formula or standard in the HVAC industry that explains the correct size opening in sq.in.,on the return air going back to a Lennox roof top unit. The Lennox unit i have is 10 tons.

I was told by an expert in the field that the unit is starving for air. He talked about the static air and didn't explain how i can check the static pressure.

The filters are clean and the evaporator is clean. I also cleaned the condenser several times.

Any help would be great. Thanks

RE: HVAC Calculating Return Air

Speaking approximately, a 10 ton unit is probably around 5000 cfm, for 5000 cfm you'd like to see around a 24x24 duct serving. The actual static pressure will depend on the length of duct.

You can check the static pressure with a pitot tube, or inclined manometer.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close