Insulate Behind Air Duct

bironacad · Mar 5, 2011

South Carolina? Are you worried about heating or cooling? Money or performance? Where is the duct carrying the air to? I was in HVAC business but need to know what you are trying to accomplish. Here duct work in an unconditioned space must be insulated to a level similar to the wall it is against, if the wall is R 12 the ductwork gets R12. The duct in your picture is insulated a tad. If you are worried about costs for heating and cooling 1/3 of your heat loss/heat gain happens through the top portion of a basements uninsulated wall. Blocks having hollows allow for cold air to sink all the way to the bottom of the wall. I live in a climate where we by law had to insulate to two feet below grade, (dirt below two feet is pretty good) now our building code states that we insulate the entire wall to min R8 right to the footing. If you are having troubles with air flow you might want to get someone with air distribution system experience to give it a look. Air duct is limited to the smallest restriction, once you have reduce a size going back up will drop air velocity and inhibit performance. Your climate is moderate?

Hope this helps

dieselscout80 · Mar 6, 2011

bironacad said:
South Carolina? Are you worried about heating or cooling? Money or performance? Where is the duct carrying the air to? I was in HVAC business but need to know what you are trying to accomplish. Here duct work in an unconditioned space must be insulated to a level similar to the wall it is against, if the wall is R 12 the ductwork gets R12. The duct in your picture is insulated a tad. If you are worried about costs for heating and cooling 1/3 of your heat loss/heat gain happens through the top portion of a basements uninsulated wall. Blocks having hollows allow for cold air to sink all the way to the bottom of the wall. I live in a climate where we by law had to insulate to two feet below grade, (dirt below two feet is pretty good) now our building code states that we insulate the entire wall to min R8 right to the footing. If you are having troubles with air flow you might want to get someone with air distribution system experience to give it a look. Air duct is limited to the smallest restriction, once you have reduce a size going back up will drop air velocity and inhibit performance. Your climate is moderate?

Hope this helps

I'm finishing the basement that was partically finished before.

The duct is a supply for the upstairs rooms and may get a duct added to it for the basement bathroom.

When I get done the wall will have insulation from the top/ceiling down about 4 feet.

We are not having any air flow issues.

SC climate well I'm from Montana so I'd say it's miserably hot

for nine months and the about right for three months.

bironacad · Mar 6, 2011

dieselscout80 said:
I'm finishing the basement that was partically finished before.

The duct is a supply for the upstairs rooms and may get a duct added to it for the basement bathroom.

When I get done the wall will have insulation from the top/ceiling down about 4 feet.

We are not having any air flow issues.

SC climate well I'm from Montana so I'd say it's miserably hot for nine months and the about right for three months.

I imagine Montana worries more about heating? Anyway what you will be concerned with is condensation on cold ductwork in a warm moist space. The ducting we use here for residential is sheet metal and we would wrap it with foil backed fiberglass, your ductwork appears to be a flex duct with insulation already on it. Because your ambient temperature from room temp to outside temp would not be relatively large I would imagine that minimal insulation would be OK. Again though an inspection from a local installer would give you local procedures and practice and would be you best bet for an accurate strategy or approach. A couple of bucks now could save you headaches later. Get the right information, like they say when in Rome do what the Romans do. Maybe talk to your neighbours as to what is what for your area. Hope this helps. :thumbsup: