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Cold Air Returns.........
Old 12-18-2008, 11:20 PM   #1
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Cold Air Returns.........

With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong.........
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Old 12-18-2008, 11:23 PM   #2
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i'd guess you want to use the uppers in winter, and lowers in summer....easier to heat hot air that rose, and easier to cool cold air near the floor...thus the unit will be more efficient?


just a guess


no home i've ever been in has louvers on the cold-airs...they both stay open all the time...and i've cleaned thousands of ducts
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Old 12-19-2008, 12:34 AM   #3
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With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong.........
I've never seen this, either. You've got adjustable louvers on the return air grills? And you adjust them differently for the different seasons? This is a new one on me.
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Old 12-19-2008, 04:58 AM   #4
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Summer: High return, High supply. Pulls hot air from ceiling area, dumps cold air at high level.

Winter: Low return, low supply. Pulls cold air in from floor level, puts heated air at floor level, then it will rise.

This works if supply and return are well separated, say 8' or more.

Ductwork may have adjustable dampers. If so set them so more airflow goes to colder areas of house.

Hope this helps.
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Old 12-19-2008, 02:26 PM   #5
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I have louvers on the bottom grills, not the top, which are fixed. I have them in each bedroom anda couple downstairs...........
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Old 12-19-2008, 02:38 PM   #6
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I have louvers on the bottom grills, not the top, which are fixed. I have them in each bedroom anda couple downstairs...........
I'd say open bottom louvers, use plastic film and or magnetic strips/ covers to block the top returns.
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Old 12-19-2008, 06:15 PM   #7
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I'd say open bottom louvers, use plastic film and or magnetic strips/ covers to block the top returns.
Are we sure that deliberately blocking the fixed return grills with plastic will not starve the furnace for return air? A "Manual D" calculation would be needed in order to be sure. If the ductwork is matched to the register/grill sizes, then the effective return vent area should be larger than the supply register area--sometimes a lot larger depending on the restrictions posed by the filter.

If you inadvertently close off too many return vents, you'll reduce the efficiency of your furnace (just as a very dirty filter would). It could also damage your heat exchanger or fan motor.
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Old 12-19-2008, 06:47 PM   #8
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Are we sure that deliberately blocking the fixed return grills with plastic will not starve the furnace for return air? A "Manual D" calculation would be needed in order to be sure. If the ductwork is matched to the register/grill sizes, then the effective return vent area should be larger than the supply register area--sometimes a lot larger depending on the restrictions posed by the filter.

If you inadvertently close off too many return vents, you'll reduce the efficiency of your furnace (just as a very dirty filter would). It could also damage your heat exchanger or fan motor.
Agree, blocking some returns would reduce airflow. OP's problem is which ones to close. I doubt he wants to mess with Manual D.

A quick test is to measure heat rise across heat exchanger with all returns open, then lower ones blocked. If heat rise does not exceed 70 degrees F, all is well. If heat rise goes to 80 or more then can't close them off.

A rash assumption on my part is that the upper and lower registers are on the same duct, or in a stud space, then change in heat rise will be somewhat higher and not significant.

OTOH I have no real idea of OP's ducting.
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Old 12-20-2008, 12:59 AM   #9
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"With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong......... "

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I have louvers on the bottom grills, not the top, which are fixed. I have them in each bedroom anda couple downstairs...........
Usually only the supply grills are adjustable and the return grills are fixed. If the top grills are fixed.....what are you actually asking?
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Old 12-20-2008, 10:12 AM   #10
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"With regards to cold air returns in a house, what are the settings for winter and summer?I lost my scribbled notes about how to set the upper and lower grilles, and it's winter and cold, and I think they are set wrong......... "



Usually only the supply grills are adjustable and the return grills are fixed. If the top grills are fixed.....what are you actually asking?
What I am asking is WHEN do I close off the supply (lower) grilles?
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Old 12-20-2008, 11:43 AM   #11
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What I am asking is WHEN do I close off the supply (lower) grilles?


Unless you have some separate heat source, such as hot water baseboard, I can't comprehend shutting of supply registers.
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Old 12-20-2008, 11:52 AM   #12
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FD, just to be clear - you have UPPER *and* LOWER RETURN GRILLS, right? These are grills that return air TO the furnace.

Do *both* the upper and lower have adjustment flaps to them?

I think some people are getting confused about what grills you are talking about. I think I have seen upper & lower grills with flaps, but it's rare.

If that's the case, I'm pretty sure you want to draw the cold (lower) air back to the furnace. I think 'the fed' has it backwards - it might seem 'easier' to heat the hot air, but a furnace is more efficient with a higher temperature differential, so you want to feed it cold air so that cold air can absorb more of the warm furnace. Otherwise, that heat just goes up the chimney. We don't want ot make it 'easy' on the furnace, we want it to work hard!

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Old 12-20-2008, 12:45 PM   #13
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FD, just to be clear - you have UPPER *and* LOWER RETURN GRILLS, right? These are grills that return air TO the furnace.
-ERD50
I don't know if I am using the term "cold air return" correctly. In each bedroom I have a vent about 7 feet off the ground, and a vent with an adjuster directly underneath it. Inside the wall is a tube/duct that I have to assume carries air back and forth in that room.

The question is: Do I CLOSE the lower vent in summer, or winter, forcing the air in that room around? Does that make sense??:confused:
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Old 12-20-2008, 12:51 PM   #14
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I don't know if I am using the term "cold air return" correctly.
If you open all the grills/registers ad turn on the furnace, which ones does air blow out of? Those are the "supply air" registers.

The grills from which air does not blow out are called "return air" vents.

In many "regular" (low to medium-end) houses, the "return air" vents are not located in the individual rooms, they are just somewhere central (i.e. one or more in a central hallway, or just a single one at the furnace) and the builder just cuts the doors to the bedrooms abot an inch short of the floor to alow the air to leave the room and find the central return air vent. Some homes have more complex systems with return air vents in individual rooms.

The best way to know what you've got is to turn on the furnace/fan and see where the air blows out.
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Old 12-20-2008, 01:00 PM   #15
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In each bedroom I have a vent about 7 feet off the ground, and a vent with an adjuster directly underneath it. Inside the wall is a tube/duct that I have to assume carries air back and forth in that room.
Well, it won't carry air back *and* forth - it will do either one or the other. Either to the furnace (Return), or from the furnace (Supply)That might be adding to the confusion.

OK, so one 7' off the ground, and how far below is 'directly below', like inches below, or do you mean 'directly in line with', but two feet from the floor ? If one is directly in line with (vertically) the other, I'd assume that they are on the same duct. But, enough assuming....

As samclem is getting to - run the furnace and use a tissue paper to see which ducts are blowing out (supply), and which are sucking in (return).



Quote:
The question is: Do I CLOSE the lower vent in summer, or winter, forcing the air in that room around? Does that make sense??:confused:
Depends on all of the above.

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Old 12-20-2008, 01:14 PM   #16
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FD: Aren't you glad you asked this simple question?
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Old 12-20-2008, 01:16 PM   #17
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As a point of reference, all my return air ducts (suck) are in the walls at floor level, and all the supply vents (blow) are in the ceiling.
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Old 12-20-2008, 01:45 PM   #18
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FD: Aren't you glad you asked this simple question?
There's no such thing as a simple question.

And, it all depends on what you mean by "simple". You see, the answer always is: "it depends".


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Old 12-20-2008, 02:29 PM   #19
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There's no such thing as a simple question.

-ERD50
To the contrary, this thread started with one.

The problem is the answer. Depending on the assumed expertise of the questioner, the answer can be one word or a novel. We have a good start on a novel.

//end thread hijack//
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Old 12-20-2008, 03:37 PM   #20
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Well, cold air returns here tonight according to the weatherman. Who know which way the wind blows.

I like LS99's: "A rash assumption on my part is that the upper and lower registers are on the same duct, or in a stud space, then change in heat rise will be somewhat higher and not significant".

Haven't seen that here in temperate Oregon, but the thought of putting high and low supply grills in the same stud cavity, feeding the cavity, and closing lower grill in the summer cooling season and upper grill in the winter heating season sounds pretty smart - and cheap enough to do when building.
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