Adding a Duct/Vent

[omagic12]

2/2, 1100 sq. ft condo located in mid-west coast of Florida.

I am adding a duct run to cool/heat an enclosed 10'x12' patio. New 2.5 ton, 15 seer Rheem split system installed 4 months ago. Before the ac unit was installed I told the installer/owner that I plan to add a vent to the patio and to make sure the new system was sized accordingly.

I enclosed (boxed) this boot: http://www.lowes.com/pd_31696-85334-GVL ... facetInfo= with 2x4"s between the ceiling joist and anchored with screws inside boot to 2x4's. I plan to mastic the seams and collar (flex attachment) and wrap any of the boot's exposed metal with insulation. Should I caulk the space between the boot and wood enclosure on the attic side or should I stuff it with insulation?

My gut feeling is to just stuff it with insulation, because if it were to condensate caulking could make it worse and possibly grow mold.

[plummen]

Do you have a picture of the install? AC doesn't work too well without a cold air return.

[kurt]

That's what I thought initially, but a 10'x12' room on the 1st fl. shouldn't be too hard to cool. I'd put the discharge as far into the room (preferably on the furthest outside wall) as possible. An open door may provide enough return.

I'm not sure what the problem is with caulk or insulation; it's hard to visualize the situation.

Can you put up a picture?

[Marc]

I get the impression that the attic of the house doesn't extend over the patio and that you've concealed the duct serving the patio within a joist bay over that patio. I wouldn't do that. Once the duct crosses the boundary between house and patio, keep it exposed within the patio's conditioned space until it ends. There's no need to insulate this exposed section of duct.

Marc

[omagic12]

I should have been more specific. The patio/lanai is semi-enclosed, as a set of sliding glass doors were removed and has been partially walled off to separate the patio from the living room. There's also french doors that lead from the patio to the master bedroom that also provides return (gaps) even when closed. The attic extends over the patio and has about 19R worth of insulation. I plan to put a saddle starter boot a bit before the main duct elbow and 6R flex pipe to the register boot.

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[omagic12]

Duct is installed and pushing as much air as the existing ducts. I think I sweated off 5 pounds that will need to be replaced with beer. Thanks for all the replies.

[mjr6550]

If the room has a lot of glass and a roof above, one vent may not be large enough to supply the airflow that you need.

[inspector57]

If you have hot/cold spots on the outside wall, replace the straight throw grill with a ceiling grill that throws to the outside wall rather than straight down. Even better considering the low ceiling height is a ceiling grill with curved vanes to throw across the ceiling rather than onto the occupants. The idea is to throw the air across the ceiling towards the outside wall to fully envelope the room rather than blowing down your neck creating a drafty uncomfortable room. The gap around the boot and the wall should be air sealed, not just stuffed with insulation. Air flow around the boot is what causes excessive condensation. Air seal AND insulate the boot.

[omagic12]

If you have hot/cold spots on the outside wall, replace the straight throw grill with a ceiling grill that throws to the outside wall rather than straight down. Even better considering the low ceiling height is a ceiling grill with curved vanes to throw across the ceiling rather than onto the occupants. The idea is to throw the air across the ceiling towards the outside wall to fully envelope the room rather than blowing down your neck creating a drafty uncomfortable room. The gap around the boot and the wall should be air sealed, not just stuffed with insulation. Air flow around the boot is what causes excessive condensation. Air seal AND insulate the boot.

This is the vent I purchase: http://www.lowes.com/pd_64335-45311-ABS ... uct_price| . I could add this http://www.lowes.com/pd_36708-34146-APS ... uct_price| if needed. Should I seal it with caulking or spray foam? wait til dried and then cover with insulation.

[omagic12]

If the room has a lot of glass and a roof above, one vent may not be large enough to supply the airflow that you need.

Yes, there's three 3' W x 5' L windows and a glass/aluminum patio door (all are tinted) with fabric roll blinds on each. The new duct helps. but due to the windows and door it's not as cool as I hoped.

I adjusted the vents as suggested by inspector57 and in combination with this beauty: http://www.amazon.com/gp/product/B004I2 ... UTF8&psc=1 it's cool.

[inspector57]

Caulk or foam can be used at the register to ceiling connection but most grills and boots come with a foam gasket that compresses to seal when installed properly. Cover the boot all the way to the ceiling with insulation and vapor barrier ( the foil-like outer jacket) to prevent condensation.

A grill with curved vanes will move more air to the outside wall. It may not be enough and an additional vent may be needed. But, grill better suited to the room may make enough of a difference to give acceptable performance. You may have to get the right grill from an HVAC supply house rather than a big box store.

Google "Curved vane vent" to see the myriad available vents.

[Erby]

Bad insulation in the wall and none on the metal duct connector can cause issues, huh.

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[omagic12]

Caulk or foam can be used at the register to ceiling connection but most grills and boots come with a foam gasket that compresses to seal when installed properly. Cover the boot all the way to the ceiling with insulation and vapor barrier ( the foil-like outer jacket) to prevent condensation. A grill with curved vanes will move more air to the outside wall. .

Thank you I-57. The grill I purchased doesn't have curved vents, and doesn't seat against the ceiling as tight as it should. I will return it and get one with curved vent's and hopefully a thicker foam perimeter. How does this sound: I'll seal the boot inside the wood frame with this caulk: http://www.homedepot.com/p/DAP-Dynaflex ... /100035980 , coat the boot with latex duct sealer and cover with a water heater insulation blanket ?

[omagic12]

Bad insulation in the wall and none on the metal duct connector can cause issues, huh.

Every picture tells a story.. don't it? I want to avoid that.