HVAC intake vents question

[zannej]

I have posted this in the houserepair forum's hvac section, but I'm wondering if anyone here knows much about hvac systems.
We have a Trane whole house system with an inside air handler/furnace and outside condenser unit. The air handler required minimum 24"x24" intake vent but the monkeys that built this house put in two 21"x21" intake vents in the hallway and in a bedroom alcove. The water heater and HVAC air handler are up on a platform in a little raised closet.
Crappy not to scale sketch

Current situation with vents in different rooms

A single 21x21 intake vent would not be sufficient, but I'm wondering if it would work if I took the vent from the bedroom alcove and moved it next to the other vent in the hallway. Is there any reason to NOT do this?
Does the vent have to be directly underneath the air handler? That is my one concern-- that moving the alcove vent would mean the original hallway vent would get most of the suction as it is directly under the unit but the other one would not be if I moved it over next to the hallway vent.
Proposed idea (suggested by my friend):

I could re-use the metal frame and grille and close up the wall in the bedroom. I also wouldn't have to enter my brother's trash-filled room and nearly hurt myself trying to access the vent in there. My brother never cleans and his room is full of plastic bags and empty plastic bottles & food containers. It's about knee deep in some spots. The bags, bottles, and candy wrappers stick to the vent and block it off quite a bit. Plus there is a dresser sticking out pretty far so there is not much free flowing air in that area.
Pros of moving the vent to hallway would be it would no longer be obstructed and would be much easier to access for filter changes. No more fumbling around in the dark trying to find the little knob that unscrews and then trying to line up the filter properly in the dark (the lights in there don't work and he has blackout curtains).
Cons of moving it would be that it would not be directly under the unit anymore and I'm not sure if it would work as efficiently (although, with it being covered half the time it probably isn't working efficiently now-- I only have to change it once every 2 months bc it's usually blocked off with plastic bags). The hallway one has to be changed 2x per month.

Any thoughts or suggestions?

 

[zoomzoom]

What you're calling "intake vents", are commonly referred to as "cold air returns". They're there to circulate the air throughout your home. If they're all in one place as you're proposing, the other rooms won't get proper circulation.
I'd suggest you do an internet search for "HVAC cold air returns". There's lots of sites that explain what exactly they do, how they're placed and how to maintain. Here's one of the first sites on the search.
https://www.searsheatingcooling.com/cold-air-return/

 

[havasu]

As Zoom Zoom stated, your hallway would be nice and cold, but the other room would have stagnant, stale air. At my house, I went the other direction and added 3 more cold air returns, which increased my level of comfort throughout my house. The only downfall is that I have 4 filters to change every 3 months, but it provides me great coverage.

 

[zannej]

These don't look like pictures of returns that I've seen. Also, one of the problems we are having is that the vent in my brother's room sucks all of the cold air out of it and makes it too hot. He had some sort of clock that detects temperature and it got to 115°F while it was 70°F in the hallway. Doesn't help that my brother keeps mostly keeps the one in his room blocked with trash.

There are ducts in the ceiling that push air into the room. The installers said there is usually only supposed to be one of these vents in the house total and that is to allow air into the circulation chamber/space underneath the unit. They referred to it as an intake vent when they put it in. It recirculates the air that it has already pushed into the room.

However, if you think it would make things worse to move the vent I will heed that advice.
This is a sketch of the house (with the proposed changes to the laundry room and guest bathroom) showing the locations of the vents that I can recall. They are marked with blue circles with the intake vents that suck back in already circulated air marked with blue as well.

There could be more vents but I'm not recalling at this moment and need to go check. If I can get the pets off of me I will look and make revisions.
Bathroom2 has a vent that pushes air into the room but it is smaller than the others.

 

[havasu]

It is probably the waist high crap in your brother's room. Make sure he doesn't have a filter, and remember, if he keeps his door shut, he won't get air flow except what creaps in from under the door.

 

[zannej]

Revised more accurate picture (the red is the fireplace-- there is a closet with a desk on the opposite side of it). I changed the suction vents to purple.

I did not draw in the pile of trash and trash bags that covers the east door to my brother's bedroom. I also didn't draw the ladder that leans against the door in front of the vent.

I was just remembering the door "floor register" and know they sometimes have them in walls. I don't know how they all connect or work but we don't have any. My brother has at least 3 desk fans blowing in his room. His door doesn't stay shut all of the way-- it's slightly ajar because it won't stay closed properly.

My door is broken so it can't close. Mom's bedroom door closes at least.

I'm very tempted to grab a broom and start clearing up the trash in my brother's room bc he keeps kicking it out into the hallway and I have to keep cleaning it up. It bugs me. LOL. I am also worried he might injure the toe he just had surgery on.

 

[zannej]

This is the platform in the hallway (use it for storage for a few things as well). The trash on the floor is some of what I swept out of the alcove in my brother's room. I filled a 55 gallon trash bag with what I got out of there.

That red large dustpan from TSC is the mvp.

 

[viking]

Good air return is the reason a lot of mobile homes have large air gaps under room doors, not a bad idea except when we were staying at my half sisters place and she had pet ferrets that love to do funny tricks on humans, like the time one of them crawled under the bathroom door and nibbled on my wife's rear as she was sitting on the toilet, after they do things they jump away and chitter like they are laughing. We had to stuff towels under the doors to keep them out.

 

[zannej]

I love animals but never been overly fond of ferrets. My sister's dumbo friend had one as a pet and it stunk. My friend's ex had two of them and they kept biting his daughter.

Never heard of a ferret managing to bite someone on the butt while they were on the toilet before. LOL. A few stories came to mind from that.
1. In Singapore a construction worker went into the women's bathroom as the men's was out of commission. A 10ft python was inside the toilet and came up and grabbed him by the 3-piece set after he crapped on its head. It took a full crew of people to pull the snake out of the toilet and drain (while still attached to the guy) and get it to release him.
2. My paternal grandfather (who was born in 1903) had an outhouse at his childhood home. No indoor plumbing. There was a hole in the back of the outhouse below the seat. While one of his sister's was using it, he found a two-pronged stick, walked up behind, poked her in the backside with the stick while making a hissing sound, and then laughed his butt off while she ran out of there screaming with her skirt almost above her head.
3. One of my father's co-workers was on the crapper when he felt something bump him from below. Looked down and it was a venomous snake. He jumped up, grabbed his gun and shot his toilet, the sink, and the bathtub-- but still missed the snake.

When I go to replace my bedroom door (already have a door to put in) I'm going to try to see what things look like in the framing. Don't know if it is hollow or if it has the tongue and groove boards. The wall between my mother's bedroom and bathroom is hollow. The wall between my bathroom and the hall closet has tongue and groove boards. I don't know what the situation is with my brother's room though. I might get an idea if I remove the door trim though.

If it is hollow, I may consider adding in some sort of vents above the doors.

Btw, how exactly do floor registers or wall registers work? I know I can google it but I'm hoping someone here has some knowledge. I have way too many "how to" and explanation videos open right now. LOL.

 

[zoomzoom]

Btw, how exactly do floor registers or wall registers work? I know I can google it but I'm hoping someone here has some knowledge. I have way too many "how to" and explanation videos open right now. LOL.

In general and normally:
Your furnace/air handler blows the hot or cold air out through what's called a plenum. The plenum is the main trunk line. It's normally a large rectangular duct.

From the plenum, ducts (normally circular and around 6-8 inches in diameter) come out of it and routes air to each area (room). For rooms that have an exterior (outside) wall, these ducts are normally towards the outside/exterior of the room. This is because that's where the weather, be it hot or cold is trying to penetrate the walls. Putting the duct and its register on the outside tries to balance the temperature in the room. If the room doesn't have an exterior wall, the location of the duct and register isn't as important.

OK, so your air handler is blowing air into a room. That creates a high air pressure situation in that room. The pressure needs to be normalized (returned to the same pressure as the rest of the house). That's the purpose of the cold air returns. Other means of balancing the pressure are as mentioned previously by things like gaps under doors.

If you don't have a basement to run the plenum and ducts, they're run through the attic then down into each room.

 

[zoomzoom]

BTW, looking at your furnace/air handler, the bottom portion is covered. Where are the furnace filters? If not directly under the furnace, they're most likely behind the cold air returns. There's normally a screw or clip on the top face of the grate to remove the grate itself. The filters are directly behind it.

 

[zannej]

Thanks, Zoomzoom. There are gaps under the doors for the rooms. My brother's door doesn't stay closed properly so air passes through the partial opening. My door can't shut because it is broken and there's a big chunk taken out of it so air goes out through it. Mom's room has a gap under the door.
All of the rooms have at least one exterior wall. My room and Mom's room have two exterior walls.
Those big grilles that I referred to as the intake are where the filters are. The one in my brother's room gets so little airflow that I only have to change it once every two months or so, but the one in the hallway is working overtime and has to be changed 2x a month. Might not be so much if not for pet hair. We had a dog who used to sit directly in front of it and shed. She had a very thick undercoat and I was forever having to brush her fur out of the grille and change the filter even more often.

I'll try to get another picture of the grille and the filter inside. The bottom of the air handler opens up into a compartment where air circulates underneath it. If the filters get full or the condensate line needs to be cleared sometimes ice forms and it drips. Haven't had that happen in awhile though.

 

[Frodo]

One 20x20x1 is the minimum for your return air intake
AS LONG AS the doors have 1” CLEAR annular space between top of finished floor and bottom of door for air movement
If doors are not undercut then a return grill mUsT be installed in that room

 

[viking]

I remember my foster dad's forced air oil fired heating system, when I was growing up, I seem to remember one of the return air supplies was tin nailed to the bottom of floor joists, in those days they didn't have insulation between the joists or wall studs, I also remember seeing the supply ducts wrapped with asbestos, which he may or may not have gotten from the ship yard he worked in. As Frodo has mentioned, if doors don't have sufficient space for return air, ducting will have to be run to far rooms, if the doors have adequate spacing then a hallway return air duct will work good.

 

[zannej]

Thanks, @Frodo !
I forgot to mention that there is a chunk of glass missing from one of my windows. Tenants apparently broke it and replaced it with glass that was too small. Only glass/window places in town went out of business so I keep meaning to patch it up with foil tape until we can get the budget to replace the windows. At least it faces the porch so I don't get rain and stuff coming in.

I really need to have some way of having sensors in different rooms because if it is set to cool to 70, the hallway shows as 70 but other rooms in the house are colder. If it is set to heat to 70 it will be 70 in the hallway but hotter in other rooms. My brother's room gets the hottest. It is also the oldest room in the house.

I wonder how hard it would be to slap grilles on some of the doors. My door will be replaced with solid core but the others interior doors (not counting the ones with glass) are hollow. Once we get the laundry room & guest bathroom renovated, the door on that side will be the primary one for my brother to use. Currently he uses the one near the AC because he uses my mother's bathroom and the other door is blocked off from inside his room.

Viking, when you say ducting, do you mean return ducting? And where would it go? To the circulation compartment under the AC?

 

[viking]

Yes people have installed grills on interior door for unhindered air return, if you do this you will have to install spacing wood just inside the hollow door cut out to make the cutout solid enough to screw the grills on, grills on both sides to make things look good. I fixed my post to say ducting for return air.

 

[UrbanHunter]

Looking at your drawings and pictures I have a couple of questions.
1) Is the water heater mounted on a deck or platform level with the bottom of the HVAC unit?
2) If bedroom #1's door is open most of the time is the vent is partially blocked?

If the space under the water heater and HVAC is just a big wooden box, why not place the new vent in the kitchen next to the pantry?

When I was a kid we had a house with added on HVAC, the unit was outside but the return plenum was a wooden box that used up the bottom of 2 closets to get to a hall in the center of the house, each of the closets had a small return vent and the hall had a big vent to pull air through the whole house.

 

[havasu]

I'd love to take a peek behind those vent screens in the plenum box. I'm guessing there are holes and cracks, so Z is sucking air from outside.

 

[havasu]

Zanne, BTW, this has nothing to do with you, and more with your home. To keep your A/C running in tip top condition, you need to check these things. My old box was also full of cracks and holes, making my unit struggle to keep up.

 

[zannej]

Looking at your drawings and pictures I have a couple of questions.
1) Is the water heater mounted on a deck or platform level with the bottom of the HVAC unit?
2) If bedroom #1's door is open most of the time is the vent is partially blocked?

If the space under the water heater and HVAC is just a big wooden box, why not place the new vent in the kitchen next to the pantry?

When I was a kid we had a house with added on HVAC, the unit was outside but the return plenum was a wooden box that used up the bottom of 2 closets to get to a hall in the center of the house, each of the closets had a small return vent and the hall had a big vent to pull air through the whole house.

1) No. There is a rectangular or square metal box that is open underneath extending in to the area below. Edit: Ok, it sits up above a few inches with a box that was built. Old air handler was long enough that it sat level. See video at the end. Yikes, I need to clean that lint out.
2) Bedroom 1's door is only open slightly. Enough that cats can't slip in and the ladder has to lean against it to hold it closed. The suction from the vent tends to make it want to swing in.
There is a bookcase next to the pantry & we don't have anywhere else to move it.

Yes people have installed grills on interior door for unhindered air return, if you do this you will have to install spacing wood just inside the hollow door cut out to make the cutout solid enough to screw the grills on, grills on both sides to make things look good. I fixed my post to say ducting for return air.

I forgot to quote this one so things are out of order. I think I may be able to use some of the wood edge strips from my broken door to make some framing if we decide to add grills.

I'd love to take a peek behind those vent screens in the plenum box. I'm guessing there are holes and cracks, so Z is sucking air from outside.

I got a cruddy photo of the outside. I am having to post again bc the APC the modem is plugged into shut off.

Snapped a photo when I shoved the camera inside after tipping the grille back and pulling filter out of the way:

I don't know how to set flash for still pictures yet and I was struggling to get the picture taken properly so I took a short video. You can hear my brother cough at one point if you have sound on. Man, I really need to squeeze in there with a lamp while that thing is off and clean it thoroughly. I cleaned it a few years ago-- swept, vacuumed, sealed up cracks & holes, etc. There was a hole so large that a copperhead snake got up in there, got stuck to some duct tape & died. So dead snake smell was circulating through the house.

Havasu, you're right about needing to check it. This house is a mess. Hoping my friend will be able to come out and help soon. I need to find the right sort of vacuum to clean the thing up. I want to add an electrical outlet below the light switch in the hallway so I can plug in a vacuum. The shopvac has a super short cord and all of the extension cords I can find are currently in use. Gonna have to mount the outlet a bit higher out of reach of cat and dog spray but will likely go with GFCI due to proximity to water heater AND a-hole pets. Edit: I went back and read the comment about me sucking air from outside and had a good laugh! I get your meaning. Just imagined myself doing a reverse of superman blowing in air and seeing all sorts of stuff flying through the air into my mouth.

 

[Aklogcabin]

Zoom nailed it. Having moving air in the rooms prevents those odors.
Also depending on how your furniture is fired. If not electric heat you will need make up air for the fire to burn properly. So you actually have 2 seperate systems on those air returns or supplies.
For what its worth. I went through 2 years of RHVAC back when I was younger n am certified

 

[Frodo]

You said your unit calls for a RA opening that is 24x24
You currently have 2- 21x22 openings

My suggestion
Seal off the RA in the bedroom. Undercut the door by minimum 1”
Reframe the RA opening to24x24
If 24 will not fit
Check hardware store for in stock filter sizes
You need 576 sq in
Find your filter then frame hole for filter and new grill to fit
This way, when you need a filter it is a size the store Carrie’s without a special order

 

[zannej]

24x24 will not fit. I was thinking of just moving the vent from the bedroom into the hallway and putting it next to the existing vent to have more air flow from that hallway. There is a very large opening from the kitchen to the hallway.
Part of the problem with the bedroom door is that my brother piles up trash in his room that sits against the door and would end up blocking any air. If I was going to add some sort of venting to that room (aside from the one that blows air into it) I think I would add it above the door so it wouldn't be obstructed.

My brain is not working all that well right now so I hope I'm making sense.

 

[Frodo]

If he piles up trash against the door how does he open the door?

 

[Aklogcabin]

Can you just use the hallway vent by connecting it to the bedroom vent at the bottom of the plenum. You would still be supplying to air the original design called for. Do the construction work out of sight within the duck

 

[Frodo]

That is a good idea

 

[zannej]

He has to kick a lot of stuff around, make a lot of noise and then kicks trash into the hallway.

I have no idea to do the thing with the plenum.