Air Duct Sealing

Your Old Ducts are Costing You Money!!
If your home is built before 1980 and you have high bills or comfort issues this is where to start. Look below and you will understand that YES, half the cold air you are buying is ending up in the attic.


If your home has METAL DUCTS this is the place to start. When these homes were built (before 1980) energy efficiency was not even on the list of considerations. I see this everyday and without fail, major comfort issues are always related to ductwork or the mechanical system.


Mold and mildew inside insulation on metal duct seam.
Return air duct fallen and letting in hot attic air into the duct system.


If your home has old GREY flex ducts these probably need to be replaced.
This was the first stab at flexible ducts. They were a failure. They would eventually disintegrate from exposure to UV. Now most ducts use the “silver” or “shiny” flex ducts.


Grey Flex Duct Falling apart. Typically installed between 1975-1985.
R-8 Flex properly sealed with radiant barrier outer sleeve.


How is Duct Leakage Tested?
There is process to test the air leakage of ducts called a “duct blaster test”. On new highly efficient homes the target is about 2-4% leakage. On “average” homes with flex duct (the stuff that looks like slinky’s) it is 20% or more and on homes with old metal rigid duct they often cannot even get a reading, meaning the leakage is over 40-50%. In California they are requiring duct sealing certification with the replacment of a new AC system. Read the Requirements HERE Also, here are some good videos produced by the California Energy Commission describing the benefits of reducing air duct leakage.


Where Does The Duct Leakage Come From?
Duct leakage is due to several factors: (Remember, prior to 1980 energy was cheap, plentiful and nobody really cared about their electric bill). The main cause is that the connections were never sealed to start. Also, damage (crushed or separated pipes from 3rd parties doing work in the attic) or separation from vibration over the years. Plus, they usually have about a 2 R-value of insulation resulting in a significant amount of heat gain as the air travels down the duct to the room.


Broken duct inside insulation. Customer had virtually no air in these rooms an we just followed the duct back until we found the “cold spot” and opened the insulation to reveal broken duct. Notice the dirt from years of air blowing into the insulation.
Wet, moldy and stinky. This leak was typical of every seam on te duct system. The cold air from the air conditioner duct meets the warm-moist air in the attic and instant condensation. Just think how much nasty stuff could be growing in the insulation.


What Does All This Mean?
What this means is that if you have metal or grey flex ducts, then you are either blowing half the cold air into the attic or could be pulling hot attic air into your return ducts.
Before you consider other options, the duct should be address first. Often customers fix the ducts first, and worry about the insulation later. It is pretty typical for the air coming out of the vents to drop 10-15 degrees after the ducts are replaced due to the leak reduction and added insulation on the ducts. I’ve seen so many times, I can practically predict it every time. Remember Duct SEALING and Duct CLEANING are not the same thing. Don’t bother with duct cleaning, it won’t help with efficiency.


Reduce Your Electric Usage 50% or More!
When the ducts are fixed AND insulation is added the usage often drops 30-50% or more, all rooms are more comfortable, and dust is greatly reduced after eliminating the negative pressure from the duct leaks (which constantly draws air in through all cracks, doors windows, etc.). Remember the air being pulled in is hot and HUMID. Humidity adds extra heat load into the house. Because of the high humidity, it can be 72 degrees and still feel warm. If the humidity is low, then It can be warmer and be more comfortable.

Look For Yourself
I’ve included some pictures below to illustrate just what’s going on BEHIND the insulation once you pull it back. Most people think the insulation keeps the air in, this is NOT true. Notice the discoloration of the insulation. This is caused by the insulation acting like a filter over the years from the air leaking into or out of the ducts. I’ve heard it a hundred times that “I had the ducts checked and the guy said they were fine”. Then, when you pull the insulation back you see what is included in the these pictures. It’s like trying to stop a leak with a rag. It just won’t work. Some AC contractors would rather sell you a new piece of equipment rather than fix the real problem which is the ducts.


What Now?
Tell a friend or neighbor. Homes with metal ducts (usually built before 1980) are notorious for having high bills and being difficult to keep comfortable. People search desperately for something that will make a difference, but until the ducts are fixed nothing will really have a big impact. Once the realize HALF the cold air they are buying is not ending up in their home, then it all makes sense.


Advantages of tight air ducts

  • Energy / Money Savings
  • More even room temperatures and comfort throughout the home
  • Better air quality
  • Reduction in Dust inside the home.
  • Better smelling home without musty attic smell
Metal ducts wrapped with insulation. The insulation is usually either foil or white vinyl. The insulation will NOT stop the air leaks. Remember the air is under PRESSURE. It would be like wrapping a leaky water pipe with a rag. It just does not stop the air flow.
Seam leak (notice mold and moisture) seam was connected with 3 screws only. This is just ONE seam. A typical home will have 50-100 seams.
Seam Leak. Notice the two pieces of duct are connected by only three screws and no tape or mastic.
Broken pipe (homeowner had comfort issues in two rooms) damage was INSIDE insulation and was not visible. Once the insulation was opened up the pipe had been crushed by someone climbing over the large plenum and using the duct as a foot hold.
Closeup of broken pipe. Notice the dirt stain INSIDE the insulation. This is a supply line.
1965 home – Duct Connection. Notice the gaps around the duct at the plenum. Since this connection is closest to the blower fan and under the highest pressure the leakage was probably 20% before air ever got into the duct. Factoring all the seam leaks along the run the end airflow was probably less then 30% of original air volume at the start of the duct run. This room was instantly more comfortable after replacing the duct.
Old duct connections. Notice no Mastic or sealant around connections.
Duct Elbow Leak – Notice the dark line that lines up with the seam on the duct elbow. Years of air pushing through this seam has caused the dark line on each seam.
Dark stain on return plenum. See next 2 pictures. Behind this dark spot is big air leak on the return side. This means that hot attic air is being pulled INTO the air system. Therefore, when the A/C is needed most on a hot day, the attic is the hottest, and the air being pulled into the air mix is the hottest. When people say that their A/C system can usually keep up, but not on a really hot day it is often a return air leak. This big leak is probably pulling 10-20% attic air alone.
Partial removal of insulation to reveal separated duct from plenum. This a Huge leak pulling Hot Attic air INTO the A/C system.
Full removal of insulation to reveal leak. This ONE Leak was so bad that just doing a temporary seal on it enabled the home to cool off 5 degrees (from 80 to 75). Once the ducts were completely replaced the homeowner could cool the home down to 71 degrees on a 100 degree day without any additional insulation.

This pictures show how the insulation wrapping the ductwork has become discolored over the years from dirty attic air being pulled into the duct. Once it is pulled back a little you can see the “clean” spots that were folded on the inside.
Stain around plenum. Notice dark spot is only on the side with a return air duct. This is caused from air being pulled through the whole side of the plenum.
Dirt around can lights – Home under negative pressure due to excessive duct leakage. Attic air is being pulled through the can lights into the living space to “make up” for duct leakage. Notice the dark spot around the can light. The negative pressure and unconditioned air (dirty attic air) being drawn into the brings excessive dust which often leads to a very dusty home.
Home under negative pressure. Notice the “clean spot” below where the paper was pulled off. This home is pulling air through light switches and other openings. Imagine how much air must pass through a light switch over the years to cause the insulation to discolor due to dust?
New R-8 Flex ducts installed properly and sealed with mastic. These ducts are SEALED TIGHT and with the radiant barrier sleeve and R-8 insulation will greatly reduce the amount of heat gain into the ducts. Often the air coming out of the new ducts will drop over 10 degrees compared to the old ducts.
Properly sealed seams on plenum and air handler. ALL seams must be sealed for a “tight” duct system.