Saturday, September 20, 2014

Rectifying a Flawed Kitchen Vent

A Kitchen remodel that I am working on called for an upgrade to the venting system from 4" to 6" on account of the change in the fan. The newer unit moves a higher volume of air that the existing 4" would handle.

The existing vent ran through a bulkhead above the kitchen cabinets to the outside and then through the roof and out a roof vent. Or at least it should vent out a roof vent. This was not the case in this install. The 4" flexible duct was pointed at an attic vent and left like that.

 An attic vent is supposed to remove air from the attic through convection and should not be used to vent any devices under pressure

What I found when I removed the attic vent

What's wrong with this??? Firstly, there is no positive connection to the outdoors. The flexible duct is merely pointed at the vent. Should the vent get blocked or squished, the air flow (in this case containing moisture) will be vented into the cold space of the attic and condense into water and lead to mold issues. Exactly what I found when I removed the ceiling to repair the bow.

After removing the vertical drywall section of the bulkhead, I ran a rigid 6" duct all the way to the end where it connected to a 6" flexible duct and up into the small attic section. 

 All joints screwed together and sealed with foil tape

6" elbow to connect to the range hood. The old 4" hole is visible to the right. Modifications to the layout of the kitchen meant a new location for the duct

From the outside I pulled the flex duct through and connected it to the supplied collar. I had to enlarge the hole and reinstall the collar. The collar has to be slipped under the top shingles so that the water flows over the vent and will not enter attic. After this the actual roof cap is installed over the collar, but under the top shingles as with the collar. What you have now is a venting system with a positive flow to the outdoors. No condensation problems any more.

The flex duct, screwed and taped with aluminium foil tape. 

Roof Cap installed 

Another view of the roof cap


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