Return Air Vents on Upper Level

[ljh]

I am hoping that some of you can share your insight with me.

I live in a two story house with forced air heating/cooling. On the upper level I have return air vents in the master bedroom and in the hallway. There are upper and lower vents in each location. I have heard and read differing views on the proper operation of these vents. It seems that the traditional, most common, but not necessarily right method is to open the upper vents in the summer(to allow hot air an escape route), and the lower vents in the winter. However, I have read from one "professional" that the correct thing to do is to have both the upper and lower vents open, that while it may seem logical to have the lower closed in summer, and the upper closed in winter, you are actually restricting air flow and affecting the performance of your equipment, because you don't have enough air flowing over the coils.

If you could share your opinions with me, it will help me to make an educated decision of my own.

Thanking you in advance...
L-J

[Irascible]

So both of the vents you speak of supply conditioned air? If so, having both open will increase total airflow. But there's no way for us to know for certain if both should be open for proper airflow. I could design a system that required both just as easily as I could design one that required just one at a time.

I'd bet that if both do supply conditioned air then whoever designed it intended for the lower ones to be closed in summer. As you say, that would be logical. But here's the catch. Few duct systems provide adequate airflow. So even if it was intended to be closed the system still probably doesn't have proper airflow through it. If it doesn't have proper airflow then leaving both open will help a little. That's probably what the professional you spoke to was thinking.

[ljh]

So sorry for not providing you with enough info!

The vents in question are strickly for return air. All my supply vents are on the floor.

It has always been my understanding that the upper/lower summer/winter rule would apply, but when I read a post on another forum from a professional stating unequivocally that BOTH vents should ALWAYS be open, it made me stop and think. This professional did not expand on his/her statement, or mention certain criteria that would make this the rule. That's why I decided to put this question out there. I wanted to see what other professionals had to say on the matter.

Thanks again...
L-J

[Irascible]

I'd leave them open. Sucking only hot air enhances the unit's ability to remove heat to some extent. The hotter the air the easier it is to remove heat from it. But on the flip side having more air flow through the system does the same thing. And the big problem with most duct systems is not their inability to suck only hot air. Their problem is typically that they don't get enough air.

The only caveat to that is if your velocity is so poor that the cold air just puddles at the floor then closing the floor returns may make sense. A well designed system will throw the air from the diffusers at a good speed. But if it just dribbles out then it may get really cold at the floor level. If that were the case then sucking from the upper vents only might be prudent.

[Edited by Irascible on 06-08-2005 at 02:53 PM]

[dash]

upper/lower-summer/winter is what a lot of people think or were taught as correct.

Return grilles ,unlike suppy grilles cause very little air movement or "air pattern" in the room.So the location has very little effcet on performance.

I'd say keeping them both open is the safest,unless you know the static(resistance to air flow) with lower versus upper open.If you know the static is okay then you can swap them by the season ,if you choose to.


I guess you could make a case ,that with both open,you are causing "better " air mixing then with just one open,so maybe that's was his thought.

[jramunni]

Tring to increase the return draw from the warmer upstairs is a great idea...but in most cases you truley can't change it enough to make much of an effect. The reality is that the thermostat is in the lower level and the cold air naturaly falls from the 2nd floor, not allowing you to have much of a cooling affect. If you want to cool the upstairs you need a thermostat located on the 2nd floor and you need to close off the air supply to the first floor ducts. This will give the run time and air delivery required to cool the 2nd floor. That will require "Zoning"!

jr

[Xavier]

ljh, Open the top for the summer and close the bottom. Then on Labor Day open the bottom and close the top.

In most applications it is the opening in the floor or ceiling joist that is controlling the flow, not the registers.

You can do your own experiment and measure the temperature in the room with all the combinations.

The last time I looked all hot air balloons went UP!

[dash]

Did the Op say the upstairs was too warm?I not sure that's a problem in this case.

[jbtecnico1]

Similar subject but different. Condo: basement with HVAC, main floor, upper level with open loft, two bedrooms, master bath. Numerous supplies at floor level, one large return (32x16) on main floor, one 16x16 return in the wall on the second floor, in the loft.

I added returns in the bedrooms: 6" dia. insulated flex in the attic, two in master, one in second bedroom. All join the loft return through the header via a 4x10 boot into a 6" round. Two t's from the 6" round accommodate my three new bedroom returns.

I get strong draw through the main return and evident draw through the loft return (using tp as a flag). Bedroom return draw is non-existent using a tp flag.

Can I cover the large return on the main floor to improve draw from the upper level for better cooling? ...without harming the blower or choking the air flow?

Or should I consider covering the return in the loft to force return through the new bedroom returns?

[dash]

The returns you ran sound very restrictive.Having the static tested while covering the other return ,will tell the tale,and I doubt it will be good..


The bedrooms need a properly ducted return,or a pass thru /jumper return to allow air to escape the room and find it's way to a main return.


The pass thru is say a 14X6 opening in the wall between the BR and hallway,with a grille on either side.

The jumper is say a 12x12 grill in the BR ceiling and one in the hall,with a 10" or 12" round flex between the two.

When using either method ,they need to be larger then you may first think,as the pressure in the duct system is not there to move the air.

[jiminator]

I once heard an analogy that set me straight on the whole return grille, high-low, winter-summer, placement issue. Take a shop vac, put the hose on the outlet, point it at a desk across the room that's covered with papers, and turn it on......The papers get blown everywhere, right? Now connect the hose to the INLET side, stand in the same place, turn on the vacuum, and see how many papers you can suck into the vac from across the room. None, right? The point here is, as was previously mentioned by Dash on this thread, that return location has very little, if any, effect on air patterns(and therefore comfort). I'd say leave both the high and low inlets open so as to facilitate the greatest possible amount of air into those particular ducts.
I love this site. It makes me think.
Jim

[beenthere]

If your supplies are in the floor and the air is hitting the ceiling, then the return high or low won't matter.

If the air isn't getting close to the ceiling, then high return is better.

But, if when you have both open, they are both pulling in air, then leave both open.

[jbtecnico1]

my ignorance...when you say measure the static, what do you mean?

Thanks for all of the other insight regarding jumps/pass-thru. I may add one or both of these items to improve my air return situation. I'll also post after I play with covering the existing returns.

Jim

[dash]

Static measurement would be by a Pro,to determne the duct systems overall resistance to air flow,and the ability to move air thru the ducts you added.

Testing would likely show that if you block the 2nd floor return ,to force the added returns to pull some air,the static woyld increase to the point that the fan can not move the required air flow,for the equipment to work properly and safely.

Simple test:Feel the air flow at supplies in Bedrooms,now block the 2nd floor return,feel the decrase in flow in the bedrooms,due to increased static.Same is tru to see if returns are needed,feel the supply with the door open,then closed the diference ,if any ,is the flow you should get ,if you add returns.


To get the returns you aded to work properly,they would need to be larger,and the duct going to the 2nd floor return,may need to be larger (may not have the space or access) as well,plus better fittings(no tees).


Your best bet is the passthru or jumper,returns unless you get a Pro to design the returns to be ducted .

[jbtecnico1]

I appreciate your input dash.

I plan to add a 12" jumper from each bedroom into a 12" ceiling grate directly above the 2nd floor return grate in the wall. I plan to use a T to join the two jumpers into one grate. With the 12" dia., a T should not be restrictive, you think?

I am willing to add a 12" grate for each jumper, I'm just trying to minimize the visual disruption in the ceiling.

I'm not going to rework the 6" returns I installed as the money is already spent and the work is done. Besides, I'm restricted to the 4x12 boot through the header to the join the 2nd floor return from the attic. This is the bottleneck I cannot overcome.

As a last resort, I may add pass thru's above each bedroom door but I'd rather not have that potential substantial compromise in (sound) privacy.

[dash]

12x12 in each room,10" from bedroom,12" from Master,ducted into a 12X24 in ceiling of hall.Based on you have double the supply in the master.

If you jion the two into one similar sized duct it will reduce air flow ,Y fitting is always better then a T fitting for air flow,if need one.