DIY Duct Repairs
Carey Residence

Fee: $180.00, paid through PayPal, less a $45.00 rebate when the "Duct
Analysis Special" was posted.


Client had received bids ranging from $2,600 up for replacing 15 damaged
flexible ducts on his three ton (that's 1,200 CFM) second floor system. He
considers himself an above average DIY-er, and contacted us to see if we could
"talk him through" the process. He believed he could save $1,500 or $2,000 by
doing the work himself, and that he would end up with a better job; we agreed on
both counts. Mr. Carey ended up spending $925 for materials, which included
$150 for
volume dampers (The required dampers had not been provided).


Field measurements over 25 years indicate properly installed flex can deliver
around 600 FPM (that's Feet Per Minute air velocity), and we use that number to
select duct sizes for ducts 8" and larger. This duct system employed two large flex
ducts for returns: One 12" (Normal design 470 CFM) and one 14" (Normal design
640 CFM), totalling 1,110 CFM normal design; that is borderline at best for a 1,200
CFM system, and the poor workmanship and long runs added considerable
resistance to flow. Increasing the size of one of the ducts was not practical
(Restrictions would have occurred due to space limitations), so an additional
return was clearly indicated.

Furthermore, there was no indication the installer understood the concepts of
"compression", "extension" or "excess length".
Above we see the two
return ducts. Below we
see the 12" return after
25 feet of flex; note that
the installer used a
different brand of flex to
continue the run. Total
distance from the unit to
the return grille
approximated 40 feet,
as compared with the
contractors use as a
limit when running flex.
Here's an image showing
the 14" return. Note the
excess length used:
There was absolutely no
need to route the flex as
high as was done;
running it lower reduced
the length required by
several feet.

In addition, a fire hazard
existed because the flex
was run too close to the
gas vent.
The images showed a
general disregard for the
need to seal air ducts:
Neither the collars nor the
slips and drives were
sealed, resulting in
wasted energy and

Mr. Carey was quite
thorough in correcting
these defects.
Before (above) and
After (below)
The first image at the left shows a typical "Before"
condition: The 12" return was "interwoven" with a
supply duct; do note the unnecessary bends
and excess lengths.

The second image at the left shows "After" Mr.
Carey's determined effort to correct the abysmal
workmanship. The 12" return is now on the left.

Not bad for someone who's "Not In The Trade",
don't you think?
Mr. Carey told us he was able to eliminate 12 feet of duct and two unnecessary
bends from the 12" return; he further stated there was a noticeable improvement
in airflow.
The improved 12" return is at the left of the image
on the left (with the foil jacket); note how the
jacket is wrinkled. It doesn't look too good, but in
fact Mr. Carey has done a very good thing: He's
used two metal adjustable elbows INSTEAD OF
bending the flex; in so doing, he's forever
eliminated any possibility of those bends
restricting flow (we've found the flex will sag as it
ages and the helix loses its resiliency).