Need HVAC expertise

I'm currently trying to figure out how big of a space I will need for my return air vent. I bought a 14x14 return air grille, but now I have a floor opening of about 14x22 (done by the previous owner).

The return air was under a closet space, but now I have actually opened up the closet space to place a stacking washer/dryer in that area.

Can I run a smaller return air opening in the floor space by covering it up (possibly)?

Not sure if I am understanding this, but if any HVAC professionals can help, it would be much appreciated!

 

It depends on a few factors like unit sizing, unit efficiency/SEER, duct sizing, etc. You’ll need to look up the installation and operation manual for your air handler to see how much air you need, and go from there. If your existing return is 14x22, I would absolutely not want to go smaller at first glance because returns are almost always undersized in houses. As a quick SWAG 14x14 is about a 1-ton unit on the low size, maybe 1.5? Something in that ballpark anyway, but again it totally depends on your equipment. Higher efficiency units often are rated to move more air which means you need larger ducting and returns.

 

Is it normal to have 2 openings on the same wall where the return air opening was? There was one grille on the wall in the hallway and one grille inside the spare room. That's what the previous owner did.

If I were to try to cover up the space (since I'm also placing my washer/dryer there) is there a downfall to making the space smaller? I have a feeling there is... but again I'm not an expert... and just trying to make the wife happy by getting that washer/dryer space completed...

 

Completely normal to have multiple returns for several different reasons. Your example could be a return path for a room without undercut doors, or just for better airflow in general.

Making the return size smaller will cut down on how well your air conditioner moves and cools air, and cutting down on airflow is a good way to burn out your supply fan motor. It has to work harder and runs hotter due to the restriction, and with less air it run even hotter due to lack of airflow cooling it down. So you end up burning up your motor long before you would otherwise have to worry about it. This also happens when you don’t replace the filter and it gets clogged.

But again, depends on your equipment.

 

Always go bigger, not smaller. Multiple returns is common, but keep in mind your t stat needs to be near a return.
You will reduce your system capacity and lifespan if you choke off the return. And for the love of Pete, change your air filter monthly!

 

Definitely understandable with air restriction resulting in a motor overworking itself. If I were to build out a box for the return air register, would I need to seal it or use any specific material to create a duct?

 

26g sheet metal, seal with “pookie” or duct sealant.

 

Pretty sure they sell 26g sheet metal at local HD?

 

And if you’re OCD about it, screw all seams with self-tapping screws, tape the seam with metal HVAC tape (no idea what it’s called although I always have some on hand but it’s metal tape with embedded threads), then pookie across the tape and both sides of it like floating a drywall seam.

But the screws and pookie will be better than most systems out there. “Duct tape” really isn’t for taping ducts, please don’t use it.

 

So that tape you have is actually for duct insulation. It’s a pain in the ass to tare?
The stuff “for” ducts is usually just silver foil tape, but if you want to get fancy they have foil tape lined with a thin layer of butyl that seals and sticks like a mofo.
Also it’s always good to do two coats of pookie if it’s exposed to the sun or rain on a daily basis.
Also I’m more of a low temp reefer guy, but I long ago and now call myself a “hvac dude” but trouble shooting is where my heart/head is at; so I’m not a expert on any of this, but little tid bits I’ve learned from all the years of being nosey……….

 

You’re probably right, now that you say it I have both at the house and haven’t used the string stuff in ages. I only ever cut it, don’t think I’ve tried to tear a piece since the first try a long time ago. I’m far from a duct guy though and not an official “HVAC dude” either, technically.

Edit: Cool secondary use: The good metal foil tape is very resistant to moisture, and does a really decent job at sealing fiberglass cracks temporarily. Like a shower pan, for instance.

 

The more return air you can get the better off you will be. As stated most are undersized in houses. I wouldn’t worry about burning up the motor per se with not enough return air. Less air flow through the fan means less work done by the motor which translates to less hp/amp draw and therefore heat. The main issue with an undersized return is you are cutting your system capacity down and risk running too low of an evaporator temp and pressure. If you run some separate returns to individual rooms, that will help your system performance and make each room with a return more comfortable.