Contact US

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!

*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

Reduce CFM or buy new unit?

Reduce CFM or buy new unit?

Reduce CFM or buy new unit?

Hello everyone!

I am having a problem deciding if I should (if it is possible) reduce the CFM of a 10T rooftop unit packaged, in order to save the owner money. He prefers not to change the RTU, so he does not have to spend "large amount of money". The point is that with new changes, the required RTU needs to be 5T. Existing 10T is double than required. So, is there a way to reduce the CFM? Existing unit(RGS119HDCA0AAAA) has only 1 compressor, and I think it cannot be used for VVT.

Thank you in advance.

RE: Reduce CFM or buy new unit?

You should typically have about 350 to 450 CFM per ton. If you can't turn down the capacity, then you can't turn down the CFM. I would tell them that they can use the 10 ton but it's more than they need. Depending on the details of your situation, it may not matter much or it may be pretty uncomfortable at times. Just like anything with HVAC, you have to look at the entire system to make a judgment.

RE: Reduce CFM or buy new unit?

Single speed unit may freeze, short cycle and so on. How did you determine you only need 5T? Did the use change from the time the 10t unit was installed?

RE: Reduce CFM or buy new unit?

In addition to problems pointed out by previous posters, the 10T unit will NOT BE ABLE to control humidity in the space due to short cycling. The WB temp in the space will rise well above 50% if the space is occupied.
You want the cooling coil to run longer, to wring out the moisture.

Sorry, but I think you will need a smaller capacity unit.

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