Basement humidity and AC return register

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Old 08-01-08, 01:38 PM
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Basement humidity and AC return register

Hi,

We live in a 35 y.o colonial. I don't have water in the basement but the humidity levels are about 75%. The basement is not airconditioned.

Someone recommended "cutting a hole" in the AC return ducts in the basement to reduce the humidity.

Will this work? My A/C pressure is pretty low. It's hard enough to cool the second floor as it is and I'm concerned how cutting a hole in the return duct will impact that.

Also, if I do that won't the humid air get into the A/C pipes and have other consequences around the house??

Appreciate any feedback. As is obvious, I have no clue about HVAC :-).

Thanks!
 
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Old 08-01-08, 07:46 PM
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Obviously, if you cut a hole in the retrun line in the basement, it will reduce the return upstairs. I would call the manufacturer of the AC first or try a dehumidifier.
 
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Old 08-01-08, 08:11 PM
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With no cooling in the basement you will have to have a dehumidfier. Cutting a hole in the duct will not help. If there is no supply air going into the basement the return in your basement will not pull.
 
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Old 08-04-08, 12:07 PM
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Originally Posted by airman.1994 View Post
With no cooling in the basement you will have to have a dehumidfier. Cutting a hole in the duct will not help. If there is no supply air going into the basement the return in your basement will not pull.
Doesn't this depend on how open the basement is to the conditioned space? How does the fan know where the air is coming from? For example, my basement is down one straight flight of stairs, with an open ceiling and no doors. The airspace is truly "shared" between floors, although the basement has no supplies or returns.

In my case, creating a return in the basement should circulate some basement air into the system, as there is no sealing barrier between the basement and first floor. Adding a supply at the same time would be ideal, but I don't want to cool the basement in the summer...only want to heat it in the winter. I can do this by closing the supply vent during cooling months and opening it during heating months.

I realize many houses don't have this basement/first floor arrangement, though.
 
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Old 08-04-08, 12:12 PM
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Also, to the OP, you could "try" opening a hole in a main-floor return in the basement. If it didn't work, you could always patch the hole, or if you have placed a close-able vent in the hole, just close it.

My guess is you have two fairly separate air spaces (basement and main floor), in which case just adding the return won't do anything. If you think of your air system as a fluid system, it's easier to envision.
 
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Old 08-04-08, 02:40 PM
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What you are trying to do will not work. With out adding air you will be making the basement a negative pressure. The air is going to go to the main return unless you add some supplys.You will have to have air from a supply to be able to have return. With out adding air you will not be able to remove air.
 
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Old 08-05-08, 07:18 AM
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So, air can't move downstairs? It's all connected, like a fluid. Getting heat to move down is difficult, but we're just talking air circulation, not heat.

As stated, my basement is very open to the first floor (no doors, open ceiling above staircase, open banister starting about 1/2 way down, etc). If air is being pulled from the basement, it can surely be supplied by the open staircase. Right?
 
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Old 08-05-08, 10:31 AM
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Two different poster in same thread!!!!!!!!!!! If you start your own thread It is easier because I don't get confused. But to answer your question if your basement is open then you can do that. But you will still have the RH problem. (or was that the other poster)
 
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Old 08-05-08, 01:01 PM
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Sorry to confuse you, but my first post had relevance to the OP's post.

Anyway, getting back to the RH problem, if the fan is pulling in damp basement air and the A/C is drying that air, won't the overall RH of the basment come down some? Seems to me it would. Of course, adding a dehumidifier makes a lot of sense as well.
 
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Old 08-05-08, 03:41 PM
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Yes will lower in basement but will raise the rest of the home.
 
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Old 08-06-08, 10:26 AM
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I have a recently finished basement. Open stairwell and plenty of returns and supplys in the basement. I can run the furnace fan 24/7, I can run the AC, it doesn't matter, I still have hi humidity in the basemen. I added a dehumidifier this past weekend. Problem solved.
 
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Old 08-06-08, 11:10 AM
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running fan 24/7 in AC mode will raise RH 5 to 10 percent.
 
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