return vent operation

[gmurr]

In each room there are two return vents directly above each other, one near the ceiling and one near the floor. I was told to close one and open the other depending on whether I was heating or cooling the space, but this year I can't remember which - open top to suck in hot air and cool it and cycle the cooler air off the bottom, or open bottom to suck in cooler air and get colder supply. Getting old I guess. Could someone explain the philosophy please. Thanks.

[mjk_na]

How many supply registers you have in each room? What are the locations?

[gmurr]

one on the floor of each room - generally in the opposite corner of the return vents (opposite wall). Living room has two on the opposite side of the room on the floor in the corners.

[dash]

Allow return from the top during cooling and from the low one during heating.It doesn't make a lot of diffrence,IMHO, but that's the "rule".

[coreytaz]

Here's why it's important to open the right ones during the right weather.


In summer your hottest and most humid air will settle up towards the top of the ceiling if you dont have fans to mix things back down. Also hot air raidates heat in the infrared spectrum. If you have a bunch of hot air at the top of the house it's actually warming everything beneath it slightly. I doubt anyone could notice it without the right equipment anyways. If you can feel it in summer it's possible your attic is radiating heat into the house and that's a insulation issue most likely.

In winter your coldest air sits towards the bottom. Sucking the hot back in really does no good other than providing slightly hotter air back at the top. When you're heating already warm air you lose efficiency. Kinda like having two water heaters in line of eachother. The first one does all the work and the other one would just be wasting gas. (That does not apply to tankless water heaters in high demand situations.)


IANAHVACM

[dash]

That's the theorey,but the return air causes almost no air movement in the room,so it can't pull all the hot air off the ceiling or cool air off the floor,from one side of the room to the other.

Now properly designed and placed supply grilles can create an air pattern that will mix the air and keep even temps., ,in the occupied zone.

[mjk_na]

Originally posted by gmurr
one on the floor of each room - generally in the opposite corner of the return vents (opposite wall). Living room has two on the opposite side of the room on the floor in the corners.

Then what I would do is, only use the top return, so that air will have to travel up before being sucked to return duct. This applies for both heating and cooling cycle. Hence you'll have better mixing.

Having both supply, and suction at the bottom will mean less efficient mixing, and less comfort.

But please check (tell your contractor to do it if you don't know) your duct calculations upon closing one return register in each room.