DIY HVAC Ducting?

[FlyBoyd]

Hello all,

I have recently purchased a house built in 1993. The previous owners replaced the air handler in 2003 and the heat pump is still doing well and under a home warranty. My question is about my ducting. It is the older rigid ducting running throught the attic which I know is not very efficient. The surface is actually cool/warm to the touch when air is moving through it. I am looking into replacing the ducting with the newer flexible type. Could this be a DIY project? My attic is very accessable. I am a pretty advanced DIYer...tile, plumbing, electrical, etc but I have not delved into HVAC. Does replacing the ducting seem insane? If not could you point me in the right direction. I obviously don't trust the big box stores for advice and getting a HVAC contractor to tell you how to do part of his job is impossible.

TIY

 

[Jadnashua]

Put some insulation over the existing stuff after you ensure the seams are sealed with the proper permanent adhesive metal tape.

 

[Sponsor]

 

[Frenchie]

The flex duct, while insulated, is MUCH less efficient in terms of air movement. The ridges create a lot of air turbulence, slows things down...

Just insulate the rigid duct, that's the most efficient combination anyways.

 

[Dunbar Plumbing]

Here's a question for the HVAC guys....


Why is it that I'm seeing 4" being used for ductwork in a home????

There's no way there's any considerable CFM flow in that equation, and how it is legal/code?


I'm starting to see this in new homes and it looks like dryer ductwork instead of heat runs.

Does a higher velocity furnace allow this method?


I don't know HVAC and I like it that way.....just thought the smaller pipe spells trouble. Seems too easy compared to all the years of seeing larger diameter piping used for furnace heat/cooling runs.

 

[Mikey]

A friend (and flyer) who build a home and hangar on an airfield I used to own had a friend who owned an HVAC company do the ducting and AC installation. They made ducting on site from rigid fiberglas/foil board -- I'm sure there's a name for it. I asked them why they didn't use the flex ducting, and they sneered and said, "that stuff's for spec houses."

Your ducts are probably resting on the rafters; just get a bunch of loose insulation of your choice and pile it on the ducts.

 

[Alternety]

There are some high velocity systems that use small flex duct. Not sure of actual size but 4" sounds about right.

 

[Jadnashua]

On some of the high velocity ducts, the branches are even smaller than that, although they may look like 4" because of the insulation. You cut a round hole in the main trunk, then use a screw-in fitting to then attach the round duct that goes to the room (usually in the ceiling). A room might have several, and if done right, is quiet and works well. They've used them on This Old House projects, and you might find that show(s) if you search their site seeing them discussed and installed.

 

[lextech]

Go down to the HVAC supply house and get some duct sealer (a.k.a. pooky) and a couple of paint brushes. Then paint the duct sealer on every joint, including start collars, in the duct work, let it dry, and then insulate. Use duct wrap, or duct board to insulate the duct work, and seal the seams of the insulation material with foil tape. Be sure to pick up a squeegee at the supply house to scrim (rub) the tape after it has been applied. Scrimming the foil tape assures a lasting bond.