Return Air Ducts

[PastorPaul]

Our supply vents for heat and A/C are all on the floor, but our return air vents are on the wall. Most of them are mounted in pairs; one high on the wall and one low on the wall.

I have been told two different stories by two different heating contractors. One told me to use the upper vents during summer and the lower during winter. The reasoning was that since hot air rises and cold air clings to the floor, the upper vents will draw in the hot air in during summer and take it into the system to cool it. Then, of course, in winter using the lower vents means you draw the cold air off the floor and replace it with the hot air from the supply vents.

The other contractor gave me just the opposite story. He told me to use the lower vents in summer, and the upper vents in winter. His reasoning was that in winter I wouldn't be trying to heat cold air, which is what I assume you want to do in winter. Also, it seems silly to me (which doesn't mean a great deal) to use the lower in summer, since you are just taking the cool air from the floor area and recooling it, but not touching the warm air at the ceiling. The reverse also seems true. If you use the upper in winter, you are taking the heated air and re-heating it, while leaving the cold air to settle at floor level.

Can someone set me straight and end all of my confusion? OK! OK! Some of my confusion. :)

Pastor Paul
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"If they don't have woodworking in heaven, I ain't going!!!"

[TDHofstetter]

T'would make the most sense to me to:

In winter, gobble up cooler air nearer the floor, heat it, and pump it back into the room heated... near the floor, where it'll tend to rise into the room.

In summer, grab that hot air next to the ceiling, cool it, and pour it back into the room cooled... near the ceiling, where it'll tend to settle back toward the floor.

...but that's me. :)

-- Tim --


Be not afraid of growing slowly,
Be instead afraid of standing still.
- Chinese Proverb -

[PastorPaul]

>In summer, grab that hot air next to the ceiling, cool it,
>and pour it back into the room cooled... near the ceiling,
>where it'll tend to settle back toward the floor.
>
>...but that's me. :)
>
>-- Tim --

Tim,

I don't have a choice on where the cool air comes in. Those vents are all in the floor. Only the return air vents are on the wall in high and low positions.

Pastor Paul
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"If they don't have woodworking in heaven, I ain't going!!!"

[deathwish2]

Pastor--

What you're getting for advice from the contractors sounds just like the contradicting advice that I've got for my ceiling fan direction . . . Some say it should it draw up in the summer to bring the cooler air off the floor and keep the warmer air up high . . . . others say it should draw up in winter to 'lift' the cold air off the floor . . . right . . . .

In the case of a ceiling fan, it really doesn't matter which way it blows unless you have 10' (or higher ceilings and never take it off the low setting . . . it circulates the air . . . . when the air it moves draws up in the center it flows back down the walls and vice-versa . . . if it blows down the center it draws for above the blades and thusly the ceiling and walls.

In your case, I agree with your instincts that the returns should be open low in winter and high in summer . . . . or just leave them all open to cut down on 'vent whistle' from the closed dampers . . . and take comfort in knowing that about 50% of your air is coming from EXACTLY where it should come from ;)

--Mark

When it comes to
woodworking and buying
tools, I always think back to
my grandfathers advice on
golf . . . "it's not the arrows,
it's the indian.''

[Grandad]

>Our supply vents for heat and A/C are all on the floor, but
>our return air vents are on the wall. Most of them are
>mounted in pairs; one high on the wall and one low on the
>wall.

Typical in well designed systems.

>I have been told two different stories by two different
>heating contractors. One told me to use the upper vents
>during summer and the lower during winter. The reasoning
>was that since hot air rises and cold air clings to the
>floor, the upper vents will draw in the hot air in during
>summer and take it into the system to cool it. Then, of
>course, in winter using the lower vents means you draw the
>cold air off the floor and replace it with the hot air from
>the supply vents.

This is the correct way.

>The other contractor gave me just the opposite story. He
>told me to use the lower vents in summer, and the upper
>vents in winter. His reasoning was

His reasoning wasn't reasoning. It was stupidity.

What you said is correct. You want to draw the hot air from the top in the summer, and the cold air from the bottom in the winter.

HOWEVER... Drawing the air from the bottom while supplying warm air to the bottom does not result in as much convection as just using the top returns all the time. If you choose to just use one vent, the top is the best one to use all the time. You can also just leave both returns open all the time. Just don't reverse it and draw from the top in winter and the bottom in summer. This will result in less comfortable air.