Adding Supply + Return to damp finished basement from Attic a good idea?

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Old 07-16-14, 09:33 PM
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Adding Supply + Return to damp finished basement from Attic a good idea?

Hello everyone!

A little background of my system:
I have a 5 ton Amana 16 SEER (Cool Only) Central Air System. Air handler and A-coil are located in attic in a typical Trunk and branch style to a colonial home's 1st and 2nd floors. The square footage of coverage is about 2900 sq ft total. There is one return on the second floor with a filter size of 30x24x5 Merv 8. The AC in my opinion has alot of spunk and has the "bring it on" attitude and does a 20 degree differential quite easily and effortlessly and maintains a constant temp of 69F (unanimous family preference) in low cool mode.

What I want to do:
Now, I have a finished basement which I wanted to cool which is roughly 500 sq feet. It does get very damp during the summer (North East) so a 60 pint dehumidifier is running on a timer + condensate pump so I don't have to dump water 2 times daily. I have a 12x8 sheet metal laundry chute from 2nd floor to basement which I can easily convert to a supply line for the basement. Considering that I have a damp basement, will it be wise to run a return duct to the basement from the attic Air Handler? Will it over-saturate the A coil due to the humid conditions of the basement? Is it even necessary to add a return in the basement? Can it be feasible with just tapping into that laundry chute and making it a dedicated cold air supply to the basement (without a return) while still running dehumidifier? The dehumidifier does make the basement warm and dry so I think the cold air to the basement would be a good idea. What do you guys think? Any suggestions are welcome.

Thanks.
 
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Old 07-17-14, 04:43 AM
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You need some way to return the air being dumped into to basement. Is the door always open to downstairs? If not, adding a return will be necessary.
Also be careful where you branch off of for supply air, you may upset the balance of the upper two floors. Some dampers may need slight adjustments.
 
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Old 07-17-14, 07:44 AM
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If the dehumidifier is right then it shouldn't be damp
 
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Old 07-17-14, 09:11 AM
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Re:

Airman.1994:
When the 60 pint dehumidifier is running, the basement is not damp anymore however it gets pretty warm and dry. It gets so warm from the LG dehumidifier that when there are occupants there, they just shut the thing off.

tomf63:
For the return, I was thinking of running a stack vent straight through the walls of the closets on the 1st and 2nd floors since they are right ontop of each other. This stack vent install is easier said than done, this job is not for a DIY'er...I don't think I can do this myself. However I could manage to add a supply to the laundry chute. I am going to be tapping into the middle of the trunk OR just adding a 6-8 inch round T or Wye to a current branch. I am going to use rigid round sheet metal all the way down to the 2nd floor laundry chute with a round to square adapter. No, the basement door is not always open. The air does not circulate well in the basement even with it open. I could however use a high cfm pedestal fan to circulate air back up the basement door, which would move the basement air upstairs towards the return.

I think if I add a supply + return to the basement, I would not need to run a dehumidifier since the AC is doing the dehumidification. This would save on the electric bill as well. I understand the concept of circulation of air so the only way to correctly dehumidify the basement would be to have both a supply and return.
 

Last edited by Pastalover; 07-17-14 at 09:30 AM.
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Old 07-18-14, 04:41 AM
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Your still going to need the dehumidifier. They are always a good option in green grass states.
 
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Old 07-18-14, 05:49 AM
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I run the dehumidifier 24/7 in the summer. The AC I use when it's hot outside. As airman said, the need for the dehumidifier will not go away because the AC is running. The vents and returns might help, though, as they can increase the movement of that dried air.
 
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Old 07-18-14, 12:41 PM
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Re

Okay I will keep the dehumidifier running. It's working very well with the little giant condensate pump 24/7.

So I am going to tap into the attic's main trunk with 8" round sheet metal to that 12x8 sheet metal laundry chute on the 2nd floor. I found an adapter to attach the two. I will see how good it cools the basement with the dehumidifier running. If I see that it gets the basement cool+dry then I will just keep it this way without adding a return. The return is going to require alot of work and labor.

Thanks all for all your input.

Cheers.
 
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Old 07-18-14, 02:51 PM
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Would it work if you put in a return from the basement to the first floor?
 
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Old 07-18-14, 03:32 PM
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Re:

Pirate,

Yea it will work. I do have a common chase wall going from attic to basement which is about 24"x27" of wall cavity....This is where the 12x8 sheet metal laundry chute is located along with a 6" draft exhaust chimney flu connected to the gas water heater and boiler in the basement.

I could go a bit further and just add a natural draft return vent to the second floor cavity going down to the basement; without any direct connections to Air Handler. The boiler does not turn on during the summer however the natural draft water heater does so I don't think there should be much of an issue with water heater mis-fire due to a return draft/drag. The Water heater and boiler have pilot lights.

OR I could use the 12x8 laundry chute as a return vent and just use the wall cavity as a supply. I don't think this might be a good idea to have a natural draft return in a space where there is a CO chimney flu. I might consider an adjacent wall to the basement stairwell,create a door vent, or just leave the basement door open and have a little help with a commercial-grade high cfm pedestal fan to re-circulate the air from basement to first floor.
 
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Old 07-18-14, 08:49 PM
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Pirate

I don't have a return on the first floor. I just have one return on the ceiling of 2nd floor stairwell with a 30x24x5 filter.

I think it might be a bad idea to send any type of ventilation naturally through that 24"x27" wall cavity without it being enclosed in Ductwork. I got a chimney flu in there that exhausts CO and heat all year round.

It is hard to create a new chase without limiting closet space or breaking the bank for demolition.

I'll keep an update of what I finally end up doing.

I think just running a supply line in the laundry chute and keeping the dehumidifier on would make the basement both cool and dry.
 
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Old 07-19-14, 05:38 AM
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The more I read this the more I'm thinking the laundry chute for cool air and you're done.
 
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Old 07-21-14, 10:44 AM
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Re:

tomf63,

Yeah that's what I'm going to do. I think I'm just thinking too much into this.

The end result will be:

The dehumidier will keep the air dry.

The cold air supply from laundry chute will keep the basement air cool and cancel out the dehumidfier's warm air output.

My understanding of what an air conditioner does is that it dries the air and makes it cold as well. In the basement, I am just going to have 2 separate sources to do just that.
 
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