Attic Duct Upgrade

Here in Oklahoma it's kind of hard to tell that Summer is right around the corner, but it is. Since air conditioning is a large portion of my utility bills I am moving my energy saving focus in that direction before it gets hot. When I bought this house the HVAC unit was virtually non-functional, and to be honest I was a tad scared to turn it on, so I had it replaced. Having a spiffy new HVAC I didn't pay much attention to it as a place to save money until I went in the attic and saw this; The main return air duct was patched together with plastic and duct tape.

Further inspection led me to this; the reason for the plastic and duct tape was because the manufacturer's sheathing on the ducts was thin plastic that had deteriorated over the years. With the sheathing around the duct falling apart the underlying fiberglass insulation is exposed and since that sheathing actually held the insulation together the underlying duct itself was exposed to the attic.

Further down the duct several more splits could be seen. I can't begin to express how disappointed I am with my (ex)air conditioning company for not informing me how poor shape these ducts were in. There is no salvaging this mess, it's a gut and replace job on the duct work. Luckily that's not too hard with flexible ducts like these.

First, a word of precaution; when walking around in your attic DO NOT STEP BETWEEN THE RAFTERS. The only thing between the rafters is Sheetrock and this can't hold the weight of an average adult. Not only will this give your house a new attic access but can be a very good way to get hurt. Take precautions, adding some walkways over the rafters around your duct work is highly advisable. I added very minimal (and temporary) walkways, I suggest you take yours more seriously.

So why are these ducts so bad? Because they're ugly? No, they're in my attic where I never see them. Do they need to be replaced because they leak air? No, the internal duct is still intact and no air leaks into the attic. These ducts need to be replaced because they are not efficient, not because they leak air but because they leak heat. Without proper insulation around the duct the cold conditioned air from the house will pass through the duct and chill it. if the duct is in direct contact with attic air, that can easily be thirty or forty degrees warmer than inside the house, that heat will be drawn through the thin duct wall heating the air before reaching the HVAC which now has to work harder to cool the warmer air.

The first thing to do was to measure the INSIDE diameter of the original duct. This is best done from inside the return vent on my system.

After I have the INTERNAL diameter of the duct, I had the precarious duty of getting measurements for the length of the ducts, I have two. With both measurements I can now order my upgraded ducts. The new ducts have a 12 inch INTERNAL diameter, just like the old ones. The new ducts are R8, which is the highest R-rating I could find. There is no reason to penny-pinch a few dollars on a lower R-rated duct as that money will be spent on higher utility bills in a season or two with lower R-ratings anyway. The new ducts also have radiant barrier sheathing!! Remember that cheesy grey plastic that was falling apart on the old ducts? That wimpy plastic wrap is replaced with a stronger wrap but also a heat-reflective wrap. With radiant barrier sheathing the heat in the attic literally bounces off the duct.

Here are some helpful links to the flexible ducts on Amazon (mine was 12-inch diameter)

12-inch, R8, 25-foot length

14-inch, R8, 25-foot length

16-inch, R8, 25-foot length

My system is a down-draft system which means the air is pulled through the return air vents are on the ceiling and pushed down through vents in the floor. A lot of newer houses have up-draft systems that pull air from return air vents closer to the floor and push that air up to vents in the ceiling. If you have an up-draft system you will probably be looking at many more ducts (usually at least one per room) but they will be smaller and easier to handle.

6-inch, R8, 25-foot length

8-inch, R8, 25-foot length

10-inch, R8, 25-foot length

Also, when ordering your ducts, don't forget the aluminum tape. DO NOT USE DUCT TAPE. Although duct tape is incredible for so many other things it actually sucks for using on ducts. Regular duct tape will become brittle, crack and peel off over time if exposed to the harsh attic temperature changes.

Duck Brand 240225 HVAC UL 723 Metal Repair Aluminum Foil Tape, 1.88-Inch by 50 Yards, Single Roll, Silver

It took about a week for my new ducts to arrive in the mail, now time to install them. First things first; we don't want the air conditioner to turn on while we are working so lets adjust the thermostat appropriately.

Time to disconnect the flexible duct from the joints both at the air unit and the vents in the house. You may have to do some cutting on the old duct depending on how tight the fit is and how much tape was used before. After the old duct is detached simply haul it out and chuck it. Mine was actually falling apart so bad that the plastic sheathing fell apart and the fiberglass insulation fell off. I reused the fiberglass insulation on a low spot in my current insulation. Waste not want not right?

With the old duct out of the way you can see where the insulation has been mucked up, better fix that before putting the new duct in.

The new duct pieces come in 25ft sections that conveniently squished accordion-style into a 4ft box. Since the shorter box fit in my attic door it was easier to bring it up still in the box. Stretching the new duct out is a careful operation as you don't want to bend or crunch it in any way. Below you can see the flexible duct inside the insulation, this needs to be extended slightly so it can be stretched over the old duct joint and fastened with ALUMINUM tape.

 

This nice cross-section shows the different layers of flexible duct. The innermost section is a heavy plastic duct reinforced with a spiral of wire to keep it from collapsing. The second layer is a fiberglass wrap that provides the R-rated insulation. The thicker the fiberglass the higher the R-rating, R-8 was the highest I could find, again don't skimp on the R-rating. The final layer on the outside is a tough plastic and aluminum flexible shell. The shell not only seals out moisture from you insulation but also acts as a radiant barrier reflecting much of the attic heat before it even gets to the insulation.

It may be a bit hard to see but the insulation is pulled back so I could pull the duct over the joint and tape the duct to the joint with ALUMINUM tape. Once the duct is secured, the insulation and radiant barrier wrap are pulled down and taped securely in place.

After both ducts have been secured on both ends you can see a nice shiny upgrade will save serious energy (and money $$$) when the sun is out this summer!

This project cost me less than $300 since I did it myself and I expect I will probably see that returned the first year and see much more in returns over the next several summers.

-ciao