I am stuck on a bathroom exhaust vent installation


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Old 02-14-15, 06:50 PM
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I am stuck on a bathroom exhaust vent installation

Our 1950s home has two unventilated bathrooms, and my lovely wife has asked me to correct this. The last (original) homeowner was good enough to go to the trouble of installing roof caps directly over these bathrooms - but never actually followed through with installing exhaust fans. So it is up to me to finish the job.

However, I do not understand how to connect a 4-inch duct to the existing roof caps. There is no fitting to accept a duct of that size. Instead what I have are square holes in the roof, covered by roof caps of a larger diameter. (Please see the photos) How do I connect a 4-inch insulated duct to this?
 
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Old 02-14-15, 07:27 PM
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Don't use the existing caps if the pipe has to be that size. Buy something that will accomodate your installation. They may have been put there just to cover the hole.
 
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Old 02-14-15, 07:37 PM
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Welcome to the forums.

Is there a damper (door) on that roof cap ?
 
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Old 02-15-15, 05:16 AM
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You will need to install a 6 inch to 4 inch duct adapter. You will then be able to hook a standard 4" duct to your exhaust fan. Some of the higher end quieter models are 6 inch port at the unit and they ship a 4" adapter with it as that is the more common size for a remodel using existing duct work. New construction, you can run what ever size you want. Obviously, more air flow out of a 6".

Master Flow 6 in. to 4 in. Round Reducer or Increaser-R6X4 - The Home Depot
 
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Old 02-15-15, 09:00 AM
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You will also need to cut underside of roof opening larger in order to get a tight fit on new adapter.
To make life easier, I would purchase a duct crimping tool, about $30.
The tool comes in handy when using several different sizes of duct and adapters.

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Old 02-16-15, 02:46 PM
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how to connect?

Thank you for the helpful answers. Enlarging the opening in the roof sheathing to accomodate a 6" adapter sounds like a good way to go. But how do I connect the adapter to the roof cap to ensure it doesn't fall out? sheet metal screws at angle?
 
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Old 02-16-15, 02:59 PM
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Mmmm... I hate to throw my hat into this ring, but I'm not sure that's the right kind of hood. What you have looks like a Lomanco #750 roof vent (used for attic ventilation) The correct kind would have been a 4" Broan roof cap w/damper, like the Broan #634.

To attach to that hood, you'd need to first of all cut some plywood out of the way, install a short sleeve, use a skinny right angle drill to get inside the sleeve and screw it to the roof cap, then put your adapter onto the sleeve. Taping all joints with foil tape.
 
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Old 02-16-15, 02:59 PM
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You can screw a take off to the roof deck with short screw and then seal to form an air tight fit.

Master Flow 6 in. Air-Tite Take-Off-ATTO6 - The Home Depot

Use a good quality metal duct tape and rigid flexible metal duct to get from unit to the the vent in the roof. Don't use plastic flex duct.
 
 

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