Return Air Capacity too Small?

[CUMULUS]

I had a 5 ton Lennox XC16 installed today. I'm a little concerned about my return air capacity. They installed one 18" flex (short run) with a 24"x20" grille and a 10" flex (25' run) with a 12"x12" grille. I am concerned that the grille size for the 18" run is too small and that I probably need to up the size and grille of that 10" run. Both grills are centrally located on opposite ends of my house and I want to stick with two for now. Would I be ok in saying they need to upsize the grille for the 18" run and upsize the diameter on the 10" run? If so, how big for each? I'd appreciate any advice you guys could lend to me so I can hit the installer up tomorrow before he hits me up for the bill. Thanks!

Added: Sorry forgot details, I live in Houston and the returns are both in the ceiling of an older 2300sf home with 8' ceilings. All work was within scope, just not positive if done correctly. I'm pretty sure a Manual D was not performed or if he would even know what static pressure is. Do I need to persuade him to make changes to the return air and/or grill sizes before I release funds?

[james80031]

Have you discussed this with the installer yet? As a contractor, I never like to hear anything that sounds like you would with-hold funds until he changes certain things that weren't in the origional scope of work. We perform work based on a certain amount of trust, even though we have all had collection problems. Was a manual D for duct sizing done? I would say that if you decide to make changes, you should expect to pay a little extra. I'm sure he realizes that this is a major purchase for you, and that you want to make sure everything is perfect. Most contractors would always be glad to make sure any additional work is done to make you happy, but there is usually an added charge.

[beenthere]

Ask him to check the static pressure.
That will tell if the returns are large enough or not.

[hvac-learning]

Are the R/A`s boxed out in a closet , under setps or cut through the wall plates? Most R/A`s grills have a chart for airflow accross the fins. I perfer Hart&Cooley R/A grill #RH45 1/3 spacing good for air flow and they are aluminum so never rust if painted and floor registers H&C #531

[Shophound]

I had a 5 ton Lennox XC16 installed today. I'm a little concerned about my return air capacity. They installed one 18" flex (short run) with a 24"x20" grille and a 10" flex (25' run) with a 12"x12" grille. I am concerned that the grille size for the 18" run is too small and that I probably need to up the size and grille of that 10" run. Both grills are centrally located on opposite ends of my house and I want to stick with two for now. Would I be ok in saying they need to upsize the grille for the 18" run and upsize the diameter on the 10" run? If so, how big for each? I'd appreciate any advice you guys could lend to me so I can hit the installer up tomorrow before he hits me up for the bill. Thanks!

Added: Sorry forgot details, I live in Houston and the returns are both in the ceiling of an older 2300sf home with 8' ceilings. All work was within scope, just not positive if done correctly. I'm pretty sure a Manual D was not performed or if he would even know what static pressure is. Do I need to persuade him to make changes to the return air and/or grill sizes before I release funds?

What has led you to believe your returns are undersized?

[CUMULUS]

What has led you to believe your returns are undersized?

Pipe sizes for 5 ton capacity? Maybe I have read too much?

[motoguy128]

Pipe sizes for 5 ton capacity? Maybe I have read too much?

A duct size calculator agrees. You'll be lucky to pull 500CFM from the 10" return with it's length, and velocity for both approach 900fpm. The smaller return would ideally be 16" and have a larger grill. That would get you're split of return air more even.

I'd guess it will be fairly noisy on the 18" return, and the 10" won't pull much air.

Another option might be to add be adding another 10" return towards the center of the house.


Off hand, 5 tons seems a little big. Houston is fairly humid, so it's sensible capacity is a little lower, but you don't want it oversized either. Did they do load calculations?

My installer was very good about making sure I was happy. A brand new system that's noisy, isn't a correct installation. I wouldn't hold back any money, you want to show good faith and give them a chance to fix it themselves. Worst case, adding another return isn't all that expensive if they decide to cut you loose.

[Shophound]

Pipe sizes for 5 ton capacity? Maybe I have read too much?

Maybe not. I ask because typically homeowners begin questioning their HVAC systems when they do not perform well, or experience operational problems. Your OP has info regarding return ducting and grill sizing, where you live, and that your system is a recent install, but not anything from you saying it's not performing well. It may not be, but we can't tell from here.

Nevertheless I agree with others that, if for no other reason than it just does not seem right to you, have your installer perform a static pressure check on the system. This really should be done as part of any install, to see if the system is within range. Unfortunately, some installers either do not know how to do this, or won't for fear it will reveal flaws in their duct layout and installation. This may not be the case with yours; he may ask you why you think there is a problem with the return air, he may not.

[scac1971]

Is the grille making noise? What kind of filter do you have? Is the filter in the grille? Is part of the house colder? Did you sleep well.

1. Pay the man. If he has been your contractor for a while you will be ok.

2. Ask him to check the static at the return plenum and supply plenum. You may be worried about nothing.