# Air Conditioner Question



## Guncho (Aug 31, 2010)

We had a new central air conditioner and furnace replaced the other day and the installer told me to do something I've never heard before.  He said you should always leave all the vents open as it's a system or something like that.  Normally in the summer I would close all the vents in the basement as it's cool down there anyway.

What do you guys think?

In mind, it's as simple as if you weren't supposed to close the vents ever, why are they adjustable?

Thanks,
Chris


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## handyguys (Aug 31, 2010)

They are adjustable for setting the initial balance of the system. After that they shouldnt be touched. Sometimes this is done with inline dampers. The goal is to have the same return and outflow. If you don't then the system will not work as designed.


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## Guncho (Aug 31, 2010)

handyguys said:


> They are adjustable for setting the initial balance of the system. After that they shouldnt be touched. Sometimes this is done with inline dampers. The goal is to have the same return and outflow. If you don't then the system will not work as designed.



I'm talking about the vents where the cold air comes out of.  Wouldn't you want to adjust these as the seasons change?


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## handyguys (Aug 31, 2010)

no - those end vents push cold (or warm) air into the room. That air needs somewhere to go, hence the corresponding return vents. If you close the end vents and the returns are sucking air from the room (creating a vacuum sort of) and making the system work harder to provide cool (or warm) air to the other rooms.

If you want to save on cooling or heating costs you would do much better by adjusting the thermostat a couple degrees warmer in the summer or cooler in the winter.


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## Guncho (Aug 31, 2010)

Each room doesn't have a return vent.  There's like 1 or 2 on the main floor and an intake on the furnace itself.


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## handyguys (Aug 31, 2010)

That makes no difference. return should equal supply. If you decrease supply you can starve the system. The professional gave you the correct advice. Its up to you if you want to listen to it.


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## Guncho (Aug 31, 2010)

I'm sorry if I just don't get this but why would closing an outtake vent decrease supply.  Wouldn't it just be like that room doesn't exist to the system and more cold air would go to the vents that were open?

If you're not supposed to open and close these outtake vents, why is there controls on them to open and close them?


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## inspectorD (Aug 31, 2010)

Ok Guncho, HVAC 101.

You need the same total input, as you do output.

3 bags O stuff in , 3 bags O stuff out. Your home should be a closed "balanced" system or it will work to hard tryin to push 1 bag out if it becomes unballanced. The adjustable vents are there to help fine tune the balance, you do not really touch those after they are set or it gets kind of "backed up" so to speak. Like if you where to cinch up your belt after eating a large pizza yourself.
And basements need airconditioning in the summer most of all, it keeps the humidity lower and helps the A/C unit to work better. Your actually making it work really hard when you close those vents in the summer to the basement.
That's why the pro's get the $$.They go to lots of school to figure these things out.
Hope the analogies helped.


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## Guncho (Aug 31, 2010)

Ok I'm hearing you know.  My only concern now is the installer didn't "balance" the system.  He opened one vent to show my wife what he was talking about but didn't touch the others.  I guess I will just open all the vents.

Another question.  I read somewhere that I should have the fan set to on and not auto in the summer.  Is that true?


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## MSU Fan (Sep 2, 2010)

What about the cold air supply in the bathroom?  My bathroom does not have a return. ???


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## delstu (Sep 19, 2010)

HVAC 102: Not all HVAC companies follow the designers specifications. They cut corners to cut costs.

Having 2 returns on the first floor and an intake on the furnace itself is not a closed system!

Seldom does a design naturally balance out. There are too many variables in air flow dynamics depending on the type of medium used. That's why vents are adjustable. HVAC systems provide both heating and cooling and often require different vent adjustments depending on the season.

Since you have an open filtered intake on the side of the furnace, intake will always have more capacity than output.


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## silentdub (Oct 1, 2010)

Guncho said:


> We had a new central air conditioner and furnace replaced the other day and the installer told me to do something I've never heard before.  He said you should always leave all the vents open as it's a system or something like that.  Normally in the summer I would close all the vents in the basement as it's cool down there anyway.
> 
> What do you guys think?
> 
> ...



 Adjust as necessary.


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## profenx (Oct 10, 2010)

wow i'm confused. I have central air and heating on same unit. I have vents in every room (even the bathrooms although they are smaller vents) I thought if i closed the bathroom vents and some room vents i will get more air out of other vents like the family room which is bigger and takes longer to cool.  I have a large filter in the hallway. is this the intake? or is it the return? what the freak is a return? Anyhow i should leave every vent open? adjust the room vents so that they feel the same temperature and that should improve my system? Cuz it takes forever for the 20x20 family room to cool but my bedrooms cool much faster.

Sorry if this is common sense. Thanks for the advice. I've never heard of keeping the vents open to. all new.


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## paul52446m (Oct 12, 2010)

I have been doing heating for 40 years and this is how i engineer a house.
 First take a heat loss on every room of the home. This tells me what size furnace i need. Furnaces come with different blowers and speeds. So to get the right blower i need, we use a rule that we find out the cubic of air in each room, and all the air in the home should be able to go through the heating and cooling unit 5 times per hr. so we can properly treat the air. So now we convert heat needed in each room into CFM of needed in each room. From that we lay out our duct system.
 We can balance the system, but people have different wants and needs.
 You need to move enough air through the furnace so you don't over heat it. You also need to move enough air across the cooling coil so it wont freeze up, But normally turning off 2 or 3 hot air reg. will not effect you system that much. It will just up the static pressure and move a little air out the other open. If you go into a bedroom and shut the door and close the hot air open, when you furnace comes it will pull a fast vacuum on the room and then you will not get any more air flow out of the room.
 So in a base in the summer most people will close some of the opening.
 In a upper story you have to close the opening down some in the winter, and open them back up in the summer time to cool it.    Later Paul


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## delstu (Oct 20, 2010)

profenx said:


> wow i'm confused. I have central air and heating on same unit. I have vents in every room (even the bathrooms although they are smaller vents) I thought if i closed the bathroom vents and some room vents i will get more air out of other vents like the family room which is bigger and takes longer to cool.  I have a large filter in the hallway. is this the intake? or is it the return? what the freak is a return? Anyhow i should leave every vent open? adjust the room vents so that they feel the same temperature and that should improve my system? Cuz it takes forever for the 20x20 family room to cool but my bedrooms cool much faster.
> 
> Sorry if this is common sense. Thanks for the advice. I've never heard of keeping the vents open to. all new.


I became disabled before getting in 40 years as Paul did. Paul obviously did not design your system or it would have at least 1 additional supply line with vent to your family room to properly balance the system.

Not everyone in the business follows the same technique Paul does. I'm sure he has followed behind another company to correct problems many times. I know I did, quite often to correct work done by some of the largest companies in my area.


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## Scott_W (May 13, 2011)

Hey Guncho, how much did it cost you? Im also planning to buy and install a centralized aircon. Thanks.


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