AC Return question(s)

[Cherokeekid88]

Replacing my filter this morning and was trying to clean up the return a little bit and noticed that a lot of the filter is being blocked. Currently am setup to accept a 14x20x1 air filter but most of it is blocked by the bottom of the drywall and a board across the top. Ideally, I’d like to open this up a bit more, get more air flow and potentially lessen the noise that comes from the return. Based on the pics, does it seem this top board could be modified to open this space up a bit? I realize that’s also supporting another board, just trying to modify my current setup to possibly install a return that I can just flip down to replace the filter rather than unscrew the vent every time. Any input would be greatly appreciated

 

[Mac5005]

First would be to install box and duct for return and not use space as plenum that has organic materials inside the plenum.

 

[Cherokeekid88]

First would be to install box and duct for return and not use space as plenum that has organic materials inside the plenum.

That might as well been written in Chinese.

 

[Futbalfantic]

First would be to install a new box and new duct for return and not use this space as the plenum (return) that has organic materials (wood) inside the plenum (return).

that’s how I read that.

 

[moldman05]

Is that the only filter ? What size is your unit ? Does that 2x4 hold up anything?

 

[rockcity]

What Scott was saying is the return should be ducted. I actually think SMACNA requires duct for supply and return.

if duct isn’t an option, then yes I would find a way to modify that board. Your effective return size is generally the area below the board. You are killing your unit and likely drawing in unfiltered air from elsewhere due to elevated negative pressures.

 

[Mac5005]

You don’t want to draw your return air off concrete/dirt around sewer pipes and across wood/sheetrock/fiberglass insulation.

So, if that is your only location for return, widen the opening, frame it out correctly to use two filters side by side, size it correctly for your unit demand.

Box it in with galvanized sheet metal, seal it with tape and mastic, attach one or more( whatever fits) ducting to that box and connect to air handler. Seal those connections with duct and mastic.

Hard to say whether you can reduce the size of that wood in the picture without knowing what it’s for, it’s location, what it supports, it’s length etc.


It terrible to use whatever open space (plenum) as the return “duct work” bc of you don’t know what in it, or where all it’s getting air actually from and what debris that air is picking up post filter and pre air handler.

Most of that large debris will be caught by the A/c coil, where most likely when it gets cold and wet, will grow mold, and reduce the air flow.

 

[Fabrik8]

Yeah, not allowed to do joist panning for a return duct anymore, mostly because it's almost impossible to properly air seal, and pulls air from places you don't want it from (like a crawlspace, dusty areas, insulation cavities, etc.). Use whatever is easy to work with and seal properly, whether that's duct board or sheet metal, as anything you use is going to be a huge improvement over what you have.

Adding the return filter grill is the easy part. If the return filter is noisy, that's usually a function of an undersized filter with too much air velocity, or too much air velocity through a poor grill design. That's not a very large filter, and some of the velocity problems may be from the shrouding from that board. The type of filter you're using is not very restrictive (and doesn't filter a huge amount), which really points to a problem with low filter area.

 

[Cherokeekid88]

Ok, I sort of understand what you guys are saying. Here are some more pics of inside the return area underneath the indoor unit. There is a reusable filter inside the unit and then the 14x20 but that is the only return in the house.

I had our entire HVAC system replaced 2 years ago and the folks installing never said anything about the return, so I figured it was fine but after looking at it in depth, I can even see this isn’t right. We have a 2.5 ton system for a 1500 (ish) sqft house

that first pic also shows the support board that is secured to the board needing to be modified

 

[Fabrik8]

Is the black panel the reusable filter, and if so what is that round sheet metal duct coming in next to it?

I'm assuming the reusable filter didn't exist before the new unit was installed, else there wouldn't be the 14x20 filter on the wall.

 

[rockcity]

Looks like you could easily build some duct to slip in there and hook up to your unit. Well, not “easy” but doable.

honestly, I’d call the HVAC contractor back and tell them to do it right. If you paid for a new system, they have an obligation to do it correctly. Requirements 2 years ago are no different than now and should have been done right back then.

 

[Mac5005]

Those pics make me cringe.

Is that white pvc pipe the condensate drain? If so that’s not even close to correct.

Is your house on a concrete slab?

If it were mine,


I’d open that wall up around the return filter, seal the slab where the stuff goes down,

Install Insulation board and then galvanized sheet metal and seal with mastic, working my way out.

Install new filter grille assembly.

Also consider spray foaming the perimeter to turn it into a actual sealed plenum. The cost is higher, but far easier labor wise.

Best solution is get HVAC people back over and have them bring it up to meet code minimum.

And x2 on what is that metal starting collar and what is it attached to and where does it go?

 

[Cherokeekid88]

Is the black panel the reusable filter, and if so what is that round sheet metal duct coming in next to it?

I'm assuming the reusable filter didn't exist before the new unit was installed, else there wouldn't be the 14x20 filter on the wall.

Yes the black panel is the reusable filter but as far as what that is next to it, I have no idea.

 

[Cherokeekid88]

Looks like you could easily build some duct to slip in there and hook up to your unit. Well, not “easy” but doable.

honestly, I’d call the HVAC contractor back and tell them to do it right. If you paid for a new system, they have an obligation to do it correctly. Requirements 2 years ago are no different than now and should have been done right back then.

I remember asking the guys that came out about that whole setup and how I was wanting to possibly open it up for a larger grille and filter and I think he looked at me and said “ nah, I’d leave it like it is”
It makes me mad honestly, I don’t know chit about HVAC and I knew less 2 years ago and wish people would just do things right. The company I used is a small outfit out of Burlington and had down work for my wife’s family for years and the recommended them to us which is why we used them.

 

[rockcity]

That return was normal back in 1955.

Today and 2 years ago, it’s not correct or to code.



I’m surprised your home inspector didn’t pick up on this. Wait! No, no I’m not. Most home inspectors are a waste of $.


If you ever sell your house, if the buyers have an inspector that’s halfway competent, this will likely come up on a report and you’ll have to decide to fix it or give $ back because it’s certainly a worthy item on an inspection.

 

[Ron]

Also in addition to everything said above, and this is very minor by comparison, you should never have two filters in line.

You are supposed to have EITHER a filter at the main unit OR a wall return filter.

Not both.

 

[Cherokeekid88]

Also in addition to everything said above, and this is very minor by comparison, you should never have two filters in line.

You are supposed to have EITHER a filter at the main unit OR a wall return filter.

Not both.

See, never knew that either. Old 30 year unit we had, had a replaceable filter AND a filter at the wall. Figured it was the same way with the new unit.

 

[Cherokeekid88]

That return was normal back in 1955.

Today and 2 years ago, it’s not correct or to code.



I’m surprised your home inspector didn’t pick up on this. Wait! No, no I’m not. Most home inspectors are a waste of $.


If you ever sell your house, if the buyers have an inspector that’s halfway competent, this will likely come up on a report and you’ll have to decide to fix it or give $ back because it’s certainly a worthy item on an inspection.

House was built in 88...

glad to know this stuff though. I’ve never taken a look at the inside of someone else’s return , so I’ve never had anything to compare it to.

 

[RatLabGuy]

Our house and the surrounding ones were buiilt in the late 60s, all of the horizontal return "ducts" are just enclosed joist spaces. That was pretty normal back then. But we als ohave individual room retruns and not just 1 big one, the filter in in-line by the blower.
Luckily here at least we have full basements so what it's sucking in through teh cracks isn't so bad, I always wen taroudn and culked everything with an HVAC sealant where I could udnerneath. It made a huge difference.
Dosn't hlep at all with the problem of the joist space not being air tight.

FYI, there is a service you can get where a technician seals off all the vents and they fill the ait with a special airisolized sealant that fills cracks. That way you end up wi tah much better seal inside of the joist spaces.
My neighbor is fixing to get this done, I'm anxious to see what the level of improvment is.

 

[Fabrik8]

House was built in 88...

glad to know this stuff though. I’ve never taken a look at the inside of someone else’s return , so I’ve never had anything to compare it to.

It's actually very common, our 1989 house has a panned joist return (it's getting deleted when the HVAC is replaced). I'm just surprised your return is that small; we have 1800sqft and have two 20x20 returns for a gaspack that's roughly the same tonnage.

 

[RatLabGuy]

It's actually very common, our 1989 house has a panned joist return (it's getting deleted when the HVAC is replaced). I'm just surprised your return is that small; we have 1800sqft and have two 20x20 returns for a gaspack that's roughly the same tonnage.

Well when all the return lines are leaky from being joist spaces, that's all you need!

 

[Cherokeekid88]

It's actually very common, our 1989 house has a panned joist return (it's getting deleted when the HVAC is replaced). I'm just surprised your return is that small; we have 1800sqft and have two 20x20 returns for a gaspack that's roughly the same tonnage.

I always thought our return was small as well...and loud.

 

[Ron]

I always thought our return was small as well...and loud.

Just as a rule of thumb, and its not 100% accurate, but typically loud means undersized

 

[shawn]

Just as a rule of thumb, and its not 100% accurate, but typically loud means undersized

Especially if it has a shitty filter on it and is still loud.

 

[RatLabGuy]

.. but typically loud means undersized

Universally true.
See also: Hondas, small dogs and guys who drive squatted die-zel trucks