flex duct

[Anonymous]

I have insulated flex duck in my attic craw space ( for heat & ac ). the craw space isn't insulated, should I put insulation over top the flex duck? If not what would be the best thing to do?

[bamaman]

Fex duct should be outlawed ! At least in attics. Works ok in basements for upflow units if installed correctly, but insulated rigid pipe should be used in ALL attics. Not much you can do with it but if it is lying flat, it would help if additional insulation is put over it. Also, make sure the attic has plenty of ventilation. Ridge vents work well if there are plenty of vent space in the overhang.

[Wgoodrich]

bamaman, why should insulated flex duct be outlawed? Seems to be a popular product for remodles needing the insulated ducting where a trunk line is not able to be installed around everything. While I do agree heat vents should distribute from the bottom of a room's wall not the ceiling or upper wall, I am confused as to your concern on insulated flexible heat ducts.

Why would you want to insulate an insulated flexible heat duct being already insulated?

Curious

Wg

[bamaman]

You are right Wg. May have been a bit harsh to use the word "outlawed". But I have seen new houses built using flex. It almost always has sags in it, which reduces airflow. The insulation used in flex duct doesnt have the same insulating value that the insulation in rigid duct has. If it is installed in an attic, the unit spends more time to cool the duct after startup. Which is why it is important to keep the attic well ventilated. Lowering the temperature of the attic space will also lower the temperature of the duct.
Many people use flex and it does work. Just not as efficiently as rigid ductwork. Didn't mean to alarm anyone, just happens to be a pet peave of mine.

[Wgoodrich]

I agree not desirable or professionally accepted to be used as a designed system in a new home. I sure comes in handy in some existing remodels where you need the flexibility in existing attics and chases.

Just thought you had something I didn't know about.

Thanks

Wg

[Mark_R]

Chez, do you perceive a problem with your current setup? While flex in the attic seems a bit unusual (for new construction *supply*) with a corresponding crawlspace underneath the subfloor, your home improvement dollar might be better spent ensuring a well ventilated attic in the summer and the use of soffet blocking panels in the winter (just don't forget to remove them in the summer!).

The above also applies if you have an 'add-on' central AC installation on an older home. Even a powered attic fan vent, for summertime use, might be in order depending on the construction of your home.

Insulating a crawl space is normally a 'bad' thing to do, in the traditional sense (bats between the floor joists)... the earth underneath your home will keep it warmer in winter and cooler in summer, but this is also an area that you will want to have vented in the summer and non-vented in the winter.

[Anonymous]

The house is 21/2 storys with craw spaces in the front and back,the back craw space has a brower unit for the 2nd and third floor. in the summer the craw space temp. is 100+.The attic has a ridge vent but no sofit vents, the sofit is only three inches wide and it's a barn style roof so when the pitch of the roof changes at the nee wall there's only about 1 '' or so gap for air to pass throw. I was thinking of putting vents in the craw space on the outside walls, maybe with fans.
I was also thinking of laying 6 inch insulation over the flew duct like a blanket (the flex duct is 4.5 r). I think it might help in the winter months, this year it was in the single digits.
I don't know if it matters but I have 2 heat pumps with oil back up 1 heat pump for the first floor with the vents in the floor and one for the 2&3 rd. floor with the vets in the ceiling

[sluciani]

Flex duct in my area is typically used to go the final few feet and make the connection to the diffusers. It's fine if you keep it to about 6 feet or less and avoid kinks and sharp bends. Sometimes you might need to use a hard elbow at the connection points to keep the kinks out. Always use insulated flex. It also provides some sound isolation from the rest of the system.

[Anonymous]

Hi,
I'm looking at installing Central A/C in a 2 story 1975 era home w/baseboard heat and no attic. I plan on a basement install of a traditional CA/C and air handler for allergies etc.

I have seen posting about Felx duct, anyone know where I can find it and installation gotchas ?
Thanks,
Frank

[Wgoodrich]

Insulated Flex duct is commonly used in remodling where flexibility is a must due to having to get around everything else. The Code allows its use. I know of no problems concerning flex duct installation as long as it is the insulated type.

If you can use a metal rigid trunk duct line across your basement ceiling then if need be use the flex duct to come off that main trunk line to each room.

Use a closet to get your rigid duct up to the second floor to its attic then again a trunk line across the attic and flex if need be to get down the walls into the second floor. Better yet is to build a bulk head along the first floor ceiling then use the flex duct along your ceiling joist fished to the outside walls.

The insulated flex ducting is same as the insulated rigid ducting considering added need of insulation. No further insulation is required.

It was mentioned that crawl spaces should not be insulated in this post. This is incorrect. The perimeter of a crawl space being the foundation around the crawl should be insulated with 2" styrofoam insulation and plastic sheeting is required on the crawl space floor. You should have a closable venting through the foundation wall for crawl space venting.

In the winter the vents should be closed and summer the vents should be open. If you have the type vents that will not close and open then cut pieces of that styrofoam to fit tight inside the vent frame then install and remove these peices as teh winter and summers change.

HOpe this helps some

Wg