Do the intake vents for an air handler/furnace need to be directly under the unit?

[zannej]

I have a whole other thread about my Trane unit but in case this question gets lost, I'm wondering if the intake vents (the ones that have filters that need to be changed) need to be directly under the air handler.
My air handler is on a raised platform in a sort of closet in the hallway (next to the water heater). There is a cavity underneath the air handler and the water heater where air can circulate. I wanted to seal off the area under the water heater but the pipes and wires for hvac were in the way.

My unit required a minimum 24x24 intake vent & when we upgraded in 2010 the installer was going to raise the platform to add one until he realized that on the perpendicular wall there is another 21x21 vent. It is in a bedroom alcove. The door swings in toward it. It's my brother's bedroom & its absolutely filthy. Full of trash to the point that the plastic bags & bottles often obstruct airflow. Something is wrong with the door so it won't stay shut or latch properly and a wooden ladder (from an old loft bed) has to be propped against it to keep it shut. This further restricts airflow to the vent. The room is full of dust but the filter only has to be changed once every 2 to 3 months whereas the hallway vent has to have a filter change 2x per month.

A friend suggested moving the vent from the bedroom into the hallway to be next to the other vent.
Crappy sketch of the bedroom and hallway layout (I didn't bother to draw the other wall across from the hvac & water heater. It has a decent width that I will have to measure later). The blue circle in front of the hvac is the condensate line.

Crappy not to scale sketch of the setup from another angle

Proposed idea:

So, would this work? Or would the vent not being directly under the unit be a problem? Would it still have sufficient airflow?
I could re-use the grille and frame from the bedroom.
Thoughts? Suggestions?

 

[Sparky617]

It depends on the layout. My basement heatpump sits on top of a plenum and the air vent is cut directly into the plenum with a filter grate in the all, much like your situation. My first floor unit, located in the basement, also sits on a return plenum, but it is ducted up to the first floor. The 20x20 filter grate is in my dining room wall. My second floor unit has two 14x20 filter grates on opposite ends of the hallway and they are ducted into the HVAC system.

Given your set up, I'd probably go with the middle picture. Having a return in bedroom one, will allow decent airflow with the door closed. Having one in the hallway will provide a return air path for the other rooms. Two 20x20s seems to be a bit of an overkill though. Both my first floor and basement are 1000 square feet and have one 20x20. The second floor is 1500 square feet and has a bit more with the two 14x20s.

 

[zannej]

To clarify, this is a single story home. There is one plenum on top of the unit in the attic. The first and 2nd setup are the same. That is the way it currently is and it is not very efficient because the 2nd vent is in my brother's room and there is so much trash that keeps sticking to the vent that there is not much airflow. It also causes his room to be hotter than the rest of the house at times. It is also very difficult for me to access the vent because of all the junk he has in the way.

 

[Sparky617]

To clarify, this is a single story home. There is one plenum on top of the unit in the attic. The first and 2nd setup are the same. That is the way it currently is and it is not very efficient because the 2nd vent is in my brother's room and there is so much trash that keeps sticking to the vent that there is not much airflow. It also causes his room to be hotter than the rest of the house at times. It is also very difficult for me to access the vent because of all the junk he has in the way

His room would be a lot more comfortable with the return vent in there. Maybe if he understood that he'd keep the trash away from the air grate. If he keeps trash there, and the door closed, the room will pressurize when the HVAC comes on and it won't have good air flow. In order for the air to flow in, it has to have a way out. Alternatively, you could cut back to back air vents above the door one on the room side and one on the hall side to allow the air to flow through.

 

[zannej]

Sparky, that is an interesting idea. I realized we don't actually have any return air vents anywhere in the house other than the two directly under the hvac unit. I remember having vents in other houses. When we lived in Virginia I remember a vent in the floor that carried sound to the basement and vice versa. We'd call out to each other through it. I don't remember if we had them in our house in California. We didn't have them in Singapore but we had min split system there. Guam we had central AC but didn't have return vents that I can recall. I remember nothing about our homes in Texas & Georgia. Don't think the house we rented when we first moved down here even had AC. I mostly remember that the floor sloped so badly we could practically fall down the hallway toward the closet.

I digressed. LOL. I took one of my not-to-scale house layout sketches and added blue circles for the round ceiling vents that blow air. These are all the ones I know about for sure. I don't believe there are any in the laundry area. . Locations are not exact. There's currently too much crap in the way to get to the laundry room are to see if there is a vent in there but I don't remember one. The purple marks next to the AC are the ones that suck air in to the compartment under it. The rest blow.

 

[zannej]

I took this picture of the hallway vent while I was in the process of cleaning up trash that I swept out of the alcove in my brother's room. Filled a 55 gallon bag with that crap. I have a large dustpan from tractorsupply that helps get big scoops of stuff.