[Firenut]

I have an unfinished expandable aread over my garage. I am in the process of finishing it out. The upstairs has its own Heat and A/C system with more than enough power to heat/cool this new space. My question, can I simply tie into the ducts to run a new duct to this room, or do I need to also consider an air return? There are two large bedrooms, a hall and a full bath upstairs on this systerm already, and there are air returns in both bedroom. Thanks for the info!

[hvac1000]

How large is expanable area?
If you say your HVAC system has enough power for the expansion what are you basing your calculations on? Is this a wing and a prayer guesst-a-ment or do you know for sure?

For duct sizing see this post.

https://www.askmehelpdesk.com/heatin...rn-358801.html

[Joshdta]

Better install some returns

[Firenut]

The area is 20' x 15', and was an option as a finished room when the house was built. The builder told me the unit for the unpstairs was large enough to handle the area - so I guess your point is good - better find out for sure. I'll take a look at the link for duct sizing, and try to find a calculator to determine if my unit if large enough for the extra space. Thanks for the help for this do-it-yourself guy with little AC experience.

[hvac1000]

Good luck with your project and post back here with how it all turned out.