# Cold air returns - floor or ceiling??



## KevinM (Mar 19, 2009)

I was doing a renovation for a customer in Ottawa who complained of cold bedrooms in the winter on the second floor of their 2 story home. 

I was upgrading moldings and insulation around windows wasn't the issue. Additional attic insulation would also help.

I recall a HVAC guy telling me some time ago that adding a second vent so there was one at the floor and one at the ceiling in the wall cavity would help if they were louvered in order to change them for the seasons.

My memory fails me as I get older but I'm grateful it is the first thing to go. :thumbup:

I recall the explanation being that in the winter, the return air should be drawn from the floor which is colder to make the room more comfortable. In the summer, the return air should be drawn from the ceiling where the air is hotter. The rational was for comfort.

The customer had his ducts cleaned after the renovation and the person doing the cleaning told him the opposite. From an efficiency perspective, this seems to make sense but I'm not an expert in this field. If comfort is your goal, which makes more sense?

Would appreciate your thoughts and my apologies if this question was asked previously as I suspected it would have been. I searched but was not able to find it.

Kevin


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## Tinstaafl (Jan 6, 2008)

I'd say the duct cleaning guy is proof of the Peter Principle.


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## Anthill (Mar 23, 2013)

I just learned something- the Peter Principle. 

Cold Air Returns? I hear this term often. I'll probably just have to get used to it as I'm not going to change the world. But are they hot air returns in cooling season?


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## Inner10 (Mar 12, 2009)

Anthill said:


> I just learned something- the Peter Principle.
> 
> Cold Air Returns? I hear this term often. I'll probably just have to get used to it as I'm not going to change the world. But are they hot air returns in cooling season?


We should just call them air returns.


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## beenthere (Mar 5, 2009)

If the supplies are on the floor, then the return being high or low makes little difference. 

If the supplies are in the ceiling, its better to have the returns low.


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## SLSTech (Sep 13, 2008)

Cold bedrooms over a garage or...
Type of ceiling - cathedral or attic?
Is the air flow required for these rooms actually making it there & if so at what temp?

unless you are using a gravity type system the location doesn't really matter to much, especially in todays newer homes. In most cases the returns & supplies are in the wall. The reason for the returns is to help not only ensure that there is enough air getting back to the system, but to eliminate pressure imbalances throughout the house. One example is the air-flow listed above - was it with the door open or closed? The results may surprise you when you shut or open said door. 

As for the question of which way assuming a real old house - the duct cleaner is wrong on more than one front though I have got to say I have never seen a reversible supply & return system


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## KevinM (Mar 19, 2009)

*Thanks*

Thanks for all the input guys. The supplies are on the floor. It's a 3 bedroom house and I'll guess about 30 years old. One bedroom has a cathedral ceiling.

It's a common issue to hear a complaint of varying temperature between floors in a two story home but this home seemed to have a considerable difference in temperature between floors and this seemed like an economical solution to try first which seems to have made a slight difference. 

I'm not sure about doors open or closed but will ask customer if he notices a difference. I'm curious on the question about cathedral ceiling. I understand it wouldn't be insulated as well as attic ceiling but are there other modifications that would/should be considered in the design of a HVAC system when there are cathedral ceilings?

thanks again,

Kevin


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## Tom M (Jan 3, 2007)

beenthere said:


> If the supplies are on the floor, then the return being high or low makes little difference.
> 
> If the supplies are in the ceiling, its better to have the returns low.


beenthere, given how the hvac unit is packaged. Have you ever seen a case where the supply and return branches merge and then a mechanical zone damper controls the flow high and low?


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## Tom M (Jan 3, 2007)

Kev open doors mean alot, also with rising heat I almost never get complaints of cold second floors.


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## beenthere (Mar 5, 2009)

Tom M said:


> beenthere, given how the hvac unit is packaged. Have you ever seen a case where the supply and return branches merge and then a mechanical zone damper controls the flow high and low?


No, I haven't.

A system like that would add the additional problem of dust blowing out the duct when it became the supply.

Return duct is suppose to have a lower air velocity then the supply. So of course, dust does tend to settle in the return ducts.


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## Tom M (Jan 3, 2007)

beenthere said:


> Return duct is suppose to have a lower air velocity then the supply. So of course, dust does tend to settle in the return ducts.



Is it supposed to be or just because of the way it works? Im thinking that the blower needs the same air going into it that it puts out. If you dont have fresh air ducts where is that air coming from? The room its in?

I can see where a there would be a difference in pressuring one side/supply and simply drawing air with friction on the return.


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## beenthere (Mar 5, 2009)

Return is "suppose" to be a lower velocity. Not a lower "volume".


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## lions_lair (Dec 18, 2014)

beenthere said:


> If the supplies are on the floor, then the return being high or low makes little difference.
> 
> If the supplies are in the ceiling, its better to have the returns low.


Exactly!


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## lions_lair (Dec 18, 2014)

beenthere said:


> Return is "suppose" to be a lower velocity. Not a lower "volume".


This^^^


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## cedarboarder (Mar 30, 2015)

Ive always put the cold air returns low. Hot air rises to the top so why put it up top?


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## beenthere (Mar 5, 2009)

cedarboarder said:


> Ive always put the cold air returns low. Hot air rises to the top so why put it up top?


So why do you want the hottest air to be at the ceiling. 

With the return high, you pull the hot air off the ceiling, and recirculate it through the house again.


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## cedarboarder (Mar 30, 2015)

beenthere said:


> So why do you want the hottest air to be at the ceiling.
> 
> With the return high, you pull the hot air off the ceiling, and recirculate it through the house again.


I never said I did. 
heat rises to the top, the cold air return is then pulling the coldest air in the room to the furnace, this negative air pressure brings the hot air down and gives the room a more consistent temp. 
A cold air return is for cold air other wise it would be called just a return.


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## TNTRenovate (Aug 19, 2010)

cedarboarder said:


> I never said I did.
> heat rises to the top, the cold air return is then pulling the coldest air in the room to the furnace, this negative air pressure brings the hot air down and gives the room a more consistent temp.
> A cold air return is for cold air other wise it would be called just a return.


Cold air returns are called cold air returns out of habit.

It draws the air regardless of the temp of the air. Placing the supply low on one side of the room and returns high draws the air across the room and across the occupants. Air circulation, is the key, from my understanding.


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## cedarboarder (Mar 30, 2015)

The only places ive ever seen cold air returns in the ceiling is undeveloped basements (easyier for the builder) and developed basements where the contractor didn't sell lowering the vent and now they have a cold basement. Why would you want to heat the hottest air in the room ?
So to answer the OP...
Having 2 air returns ( using one at time) the top cold air return is for summer. This will a/c the hot air in the room. Bottem for the winter.


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## superseal (Feb 4, 2009)

cedarboarder said:


> The only places ive ever seen cold air returns in the ceiling is undeveloped basements (easyier for the builder) and developed basements where the contractor didn't sell lowering the vent and now they have a cold basement. Why would you want to heat the hottest air in the room ?
> So to answer the OP...
> Having 2 air returns ( using one at time) the top cold air return is for summer. This will a/c the hot air in the room. Bottem for the winter.


I see a lot of new construction where the return is simply placed in the upstairs hallway ceiling and the bedrooms only get supplies :blink:

My home built in 42 has the supplies in every room and returns in all but the baths and kitchen. They're placed down low along the wall and are offset across the room. I believe those guys back then got it right...


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