Duct Design And Adding On Questions

72chevy4x4

I'm doing a little work on my own house which I enclosed an open porch and am running supply ducts to the area.

My house has one central plenum running near the center of the house and almost every supply vent is run using a 7" duct to the exterior using expandable insulated duct tubing (what do you pro's call this?).

My question is, how do you design a system like this-the same way w/ a lot of flexible insulated tubing or smaller takeoff plenum's made of ductboard keeping the flex tubing reasonably short?

Is it 'acceptable' to use the joist bay as a supply duct (by affixing duct board on bottom of joists)?

One more question if you don't mind...I saw a 4" pleated air handler filter today and it looked interesting. Does it do a much better job at filtering or merely increase the service time between filter changes because of the increased surface area?

thanks for your time guys

gregj

I'm not an HVAC guy but the one I usually use generally would run a larger metal duct to the new area and short runs off that. He rarely uses flex duct.

Can't use joist bays as supply.

I use a 4" pleated filter. Don't have to change it as often but I don't think it is more efficient than other thinner filters. I guess it depends on what thinner filter you are comparing it to.

Tom M

If its a short trunk its called a simple plenum if the trunks long its called an extended plenum.

Not my proffession but by code joist or cavity's cant be supply feeds. If you line the whole cavity with duct board it should be allowed.

hvaclover

Short, to the point, and correct. My compliments.

Dr Heat

expandable insulated duct tubing (what do you pro's call this?).


One more question if you don't mind...I saw a 4" pleated air handler filter today and it looked interesting. Does it do a much better job at filtering or merely increase the service time between filter changes because of the increased surface area?

thanks for your time guys [/quote]

First question "Flex" We only use flex on commercial jobs with a drop ceiling codes very I think the Na Building Code says 14' I limit it to 5' though there are times when we use more flex has 80% the capacity as rigid and you are not permitted to make any tight turns.

Second I'm sure there are different 4" filters available We sell Air Bear filters The advantage is the increased surface are allows a finer filtration and a longer run time. If you believe what the cut sheets say they are much more efficient