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Old 09-29-2008, 11:22 PM   #1
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Plaster Ducts


House was built in 1945
Forced Air Furnace
2 Story House

We have lived in the house for 2 years. I noticed this weekend that the 2nd floor return air ducts are not lined with metal. They are open to the plaster in the walls. They are also open to the floor joists.

I'm wondering what kind of ducts can be installed without having to break the plaster.

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Old 09-30-2008, 07:11 AM   #2
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Plaster Ducts


It is still considered accepted practice in new construction to use wall cavities and pan floor joists. What concern do you have?

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Old 09-30-2008, 06:21 PM   #3
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It is still considered accepted practice in new construction to use wall cavities and pan floor joists. What concern do you have?
It's just that the ducts have a "Smell" to them on really hot summer days. Also it would seem harder to clean.

Granted I live in central Canada and those days are rare.
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Old 09-30-2008, 08:48 PM   #4
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Plaster Ducts


Most older homes used 2x4 with 16 inch centers so you could put in a 3.5x14 wall stack. Depending on the location of the duct you could cut out the base plate and shove the pipe up the opening one section at at time. I have done this and although it is not easy it is simpler that cutting open the wall and doing it that way.

If you choose to do it this way then make sure you use S lock and screw the next section and use mastic tape to seal the joints.
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Old 09-30-2008, 09:19 PM   #5
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Plaster Ducts


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3.5x14 wall stack.
Thanks for the reply!

Can someone provide a link of what 3.5x14 wall stack looks like?
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Old 09-30-2008, 11:01 PM   #6
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Plaster Ducts


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Thanks for the reply!

Can someone provide a link of what 3.5x14 wall stack looks like?
It's just ducting that you assemble that is 3.5 inches by 14 inches and come in 3, 5, 8 and 10 foot sections. The smaller sections are easier to put into existing walls as they can be angled in. The larger sizes are for one section in a tall wall.

I just put one in at my neighbors and went over to take a picture just for you.... It even has the lath and plaster which we are replacing with sheet rock AND insulation.
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Old 10-01-2008, 12:05 AM   #7
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Plaster Ducts


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Originally Posted by Marvin Gardens View Post
It's just ducting that you assemble that is 3.5 inches by 14 inches and come in 3, 5, 8 and 10 foot sections. The smaller sections are easier to put into existing walls as they can be angled in. The larger sizes are for one section in a tall wall.

I just put one in at my neighbors and went over to take a picture just for you.... It even has the lath and plaster which we are replacing with sheet rock AND insulation.
Awesome!

This leads me to another question.

So lets assume that running the vertical is no longer a problem.

How can I run the horizontal and get the 90deg elbow join with the vertical if I can't physically get access to the elbow since it's behind plaster under the 2nd floor joists? The 2nd floor is hardwood so I don't want to cut. The 1st floor ceiling has some nice plaster work.
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Old 10-01-2008, 12:38 AM   #8
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Plaster Ducts


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Awesome!

This leads me to another question.

So lets assume that running the vertical is no longer a problem.

How can I run the horizontal and get the 90deg elbow join with the vertical if I can't physically get access to the elbow since it's behind plaster under the 2nd floor joists? The 2nd floor is hardwood so I don't want to cut. The 1st floor ceiling has some nice plaster work.
I am not sure what your situation is but if you drop the wall stack below the level of the floor you might be able to access it from below. I have attached a picture of something like that.

You can use a starter collar and attach the round ducting to that.

Or you could even use more of the wall stack and run it horizontally which I have done. It is a lot of work to get than working but it is an option.

Since the wall void is already the "duct" just drop the wall stack down from the top and secure it at the top. Most of the smell is coming from the wall part of the vent. You really don't need to connect the wall stack to the rest of the ducting since the wall itself is the duct. You just put in a sleeve.
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