Tuning system - eliminated one vent


  #1  
Old 06-13-24, 06:48 PM
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Tuning system - eliminated one vent

I'll try to keep this brief. I eliminated one duct/vent going to the master in removing a wall on the floor below. I was going to re-route it..but it would be quite a big project. This is a 2 story home with a basement.

I have about a 4 degree difference between the 1st floor and 2nd floor. The basement is always colder in the summer.

There are 18 damper adjustments in the basement. It looks like one for each vent. Sounds unusual for me as isn't there usually trunk lines? The house was built in 1950.

My question is...can I eliminate this 4 degree difference between the main level and the 2nd level with the dampers? What is the easiest way to figure out what damper is for what? The ceiling is mostly finished in the basement. I was thinking of tapping a screwdriver or something and having someone listen at each vent but maybe there is a better way? If I close each one it may not close all the way and there still might be some flow...but I am guessing.

 
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Old 06-14-24, 10:17 AM
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"...can I eliminate this 4 degree difference between the main level and the 2nd level with the dampers?"
Maybe... Is there an open path between the two floors like a stairwell or balcony? If so you are fighting a never ending battle. Sold air sinks and warm air rises. So, as long as there is a open path between the two floors the air will begin to stratify as soon as the AC turns off. One way around this is to run the air handler continuously. That way you are constantly stirring the air, preventing the cold from sinking and hot from rising.

Consider how much work you want to invest in getting the AC set just perfect. Come winter you will have the opposite problem and will need to direct more airflow to the lower areas and less upstairs. If you choose this, change the dampers twice a year approach, I would mark each damper with it's summer and winter position once you get the system balanced the way you like.
 
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Old 06-14-24, 10:29 AM
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Thanks.

In the winter it was fine because warm air rises like you said. The temperature seemed pretty even all winter between the 1st and 2nd floors.

I'm not looking for perfect. But if I could get to a 1 or 2 degree difference I'd be happy.

I'm considering other options. One would be a mini split or a mini split window unit. The benefit of that is at night I really only care about the master bedroom and don't care if it is warm in the main living areas. Installing a real mini split would be a fair amount of work due to the electrical, attaching the compressor on the outside of the 2nd floor bedroom, etc. The window units that are U shaped and are controllable with a remote might do the job. There is a small hallway with closets on both sides with a window so you wouldn't really see it much. I imagine a window unit is less efficient from an energy used point of view.
 
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Old 06-14-24, 07:03 PM
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Possible? Yes. I would simply turn on the fan and note the changes you see in output at each vent when you open and close dampers. Then write that all down so you don't have to do the experiment again. FWIW, I close two vents downstairs in the summer and three upstairs in the winter to keep my home balanced.
 
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Old 06-14-24, 07:10 PM
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Thanks for the reply. I am an HVAC novice. Does closing vents in a room actually help redistribute the heat/cold? What I mean is does it backup all the way to the furnace and go to other vents? I guess what I am asking is if I close the vents closest the the thermostat will I get what I am trying to achieve?

I had someone help me today to try and figure out what each damper (there are 21) does with mixed results. Some might not be workable (though the piece I see turns). I found 3/5 in the basement but not the other 2. The basement doesn't need A/c because 1) it is below grade and 2) we don't use it other than for storage.
 
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Old 06-17-24, 06:29 PM
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What is the point where the system becomes inefficient? For example, there are 5 vents in the basement, 7 on the 1st floor and 4 on the 2nd floor. If I close all 12 vents in the basement and 1st floor it seems like too much cold air will be forced into ducts that probably cannot handle it. Since cold air falls, I am trying to come up with a strategy but I don't know where closing vents./dampers becomes counter productive.
 

Last edited by michaeljc70; 06-17-24 at 06:41 PM.
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Old 06-18-24, 07:28 AM
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"What is the point where the system becomes inefficient?"
How do you define "efficient"?

You have a problem inherent with a multi story building using one simple (no automatic zones/dampers) HVAC system. No one setup is best for each season. But, the more you close vents & registers the more you restrict the airflow which generally hurts system efficiency though it may improve comfort in some parts of the home.

Was your ducting sized to accommodate many vents closed? We don't know but probably not. Closing one or two vents shouldn't affect the system enough to cause trouble. If you close 12 vents like you mentioned the reduced airflow could cause freeze-up issues.

The simplest issue might be to keep the air moving so it's harder for the hot to collect upstairs and the cold in the basement. Turn the system's fan "on" and leave it for a few days or week to see how you like it. The air handler fan will run continuously while the AC compressor will turn on/off as needed.

And keep in mind that everything you are mentioning is dealing with the output of the AC, the vents and registers. What about the other half... the cold air return(s). It's location will also affect airflow in the building.
 
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Old 06-18-24, 09:55 AM
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Thanks. I was thinking about the cold air returns. They have dampers also. I don't know if closing some of those would be useful for the summer.

My smart thermostat has sensors and I can make it run until the bedroom reaches any temp I want. Obviously though if it is 72 in the bedroom and 68 on the main level that isn't great.

The ducts are various sizes. If I can close a few of the bigger vents on the main level and run the a/c to get the bedroom where I want it it might not be so bad. The vents/dampers in the basement are all closed.

I've tried running the fan more. I suspect that may help when it isn't real hot but if it is real hot the a/c is going to be running a lot anyway.
 

Last edited by michaeljc70; 06-18-24 at 11:30 AM.
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Old 06-18-24, 02:34 PM
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Not for nothing but I never close air returns, only vents.
 
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Old 06-20-24, 01:23 PM
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My basement is finished but there are no cold air returns. They covered up what I think was one on the cold air stack. Would it be beneficial to open this up and put a vent cover on it?

There are no bedrooms in the basement. There is a large family room, bathroom and mechanical room.

 
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Old 06-20-24, 07:14 PM
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Either you have both vents and returns in a space or you have neither is the way I look at it. I close some vents downstairs in the summer but not all so I have returns in that space as well.
 
 

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