How to size an HVAC unit?

**mdevera211** · 10-18-2009, 03:21 AM

While waiting for a dream job, I'm doing service work on my own and I notice homes that are only 5 years old have undersized units? Can anyone tell me what size an HVAC unit should be or how to size a unit for homes? I had a service call for a condensing unit not running and I noticed it was an obviously undersized unit for the home. It was a 3100sf home with a 3 ton or 3 1/2 ton condensing unit. Could anyone tell me what size unit that home should have? I'm thinking it should at least have twice what it currently have. The customer said it takes a long time to cool the entire house.

**the dangling wrangler** · 10-18-2009, 06:02 AM

Here's one way.

http://hvaccomputer.com/talkref.asp

**beenthere** · 10-18-2009, 06:34 AM

Guess that means you think a 4000 sq ft home should have more then 2 tons of A/C.

Sq ft alone. Does not indicate what size A/C a house needs.
Use the posted link. And you will be able to learn how to size.

Next. An under sized duct system. Will make a properly, and an over sized A/C take long to cool the house. A/C is not suppose to be a quick process. Since in most areas. Dehumidification is an important part of the cooling process.

**jdavis72** · 10-18-2009, 01:02 PM

And you're a service tech?

**trey r** · 10-18-2009, 02:55 PM

Originally Posted by mdevera211

While waiting for a dream job, I'm doing service work on my own and I notice homes that are only 5 years old have undersized units? Can anyone tell me what size an HVAC unit should be or how to size a unit for homes? I had a service call for a condensing unit not running and I noticed it was an obviously undersized unit for the home. It was a 3100sf home with a 3 ton or 3 1/2 ton condensing unit. Could anyone tell me what size unit that home should have? I'm thinking it should at least have twice what it currently have. The customer said it takes a long time to cool the entire house.

Was it a 3 ton or 3 1/2 ton? Since you obviously don't know how to size equipment how are you determining it's undersized?

**the dangling wrangler** · 10-18-2009, 03:04 PM

Hey BT, why not tell this guy about applying for professional status.
He's got the post count. Seems like he's trying to learn something.

**beenthere** · 10-18-2009, 03:09 PM

Originally Posted by the dangling wrangler

Hey BT, why not tell this guy about applying for professional status.
He's got the post count. Seems like he's trying to learn something.

What. You couldn't copy and paste from one of my post with it in.

OP:

You have the post count, apply for Pro Membership.
Use this link and Apply for Pro Membership

Once accepted, you have access to the pro tech forums. Where you can ask and get answers to technical questions.

Plus, you also have access to the Pro Educational Forums.

All of it is free.

**the dangling wrangler** · 10-18-2009, 03:27 PM

Originally Posted by beenthere

What. You couldn't copy and paste from one of my post with it in.

OP:

You have the post count, apply for Pro Membership.
Use this link and Apply for Pro Membership

Once accepted, you have access to the pro tech forums. Where you can ask and get answers to technical questions.

Plus, you also have access to the Pro Educational Forums.

All of it is free.

That's the ticket!
I'll bet you agree. No need to give the guy a hard time. Let's try and help him.