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Duct & Air Sealing

leaky ducts are a huge energy waster!

At we would LOVE to sell you some radiant barrier foil. However, our FIRST priority is to help you save money and make your home more comfortable! If you have an older home check the ducts for leakage before you ever think about buying radiant barrier or more attic insulation. If your air ducts are leaky, several things can be happening. Leaks on the SUPPLY side push hot or cold air INTO the attic instead of your home. This is money wasted and causes outside air to be pulled into the home due to negative pressure. Leaks on the RETURN side cause hot, humid dirty attic air to be drawn directly into your air conditioner. This is like running a hair dryer in your refrigerator and will cause the home to be hot, humid and inefficient.


The key to preventing ANY moisture problems is to seal, seal, seal holes in the ceiling under the foil. If you can prevent the water vapor from condensing then there is usually never an issue to deal with. Oftentimes customers lean on the conservative side and cut holes in the radiant barrier above potential moisture spots to allow extra drying potential (ability for water vapor to pass through).


Older ducts, especially metal ducts, are notorious for leaking. Studies show that there is generally a direct correlation between the age of the duct system and the percentage of duct leakage. Additionally, wrapping a duct with insulation does virtually nothing to reduce duct leakage; it’s like wrapping a leaky pipe with a rag – even if it slows down the flow, it still will not completely stop a water leak.


The duct collar should be sealed with duct mastic to prevent air leakage and make an air tight seal.

Old ductwork separated from the plenum box can be seen in this photo.

The dark line on the insulation is caused from years of air being pushed out of the metal seam.

Energy Saving Tips:

Check for leaky ducts. This is probably the most overlooked area on most homes. If the air in your ducts were water, your attic would probably fill up within a few minutes. In California, they require duct testing/sealing to be performed with the installation of a new A/C unit – read about it here. Many homes (even newer homes) have duct leakage of over 15%; in older homes with metal duct work, the leakage is usually OVER 50%! Don’t waste your time on radiant barrier or insulation until your ducts are tight. Here are some industry study results on duct leakage and other air conditioning problems.


Find possible sites for air infiltration/holes in your home. Once again, think of your home like a refrigerator. It does not matter how much insulation you put on it, until you close the door it’s going to run all the time. Can lights, attic doors, windows, doors, etc., anyplace air can get in needs to be inspected. Seal them up!


Inspect areas of thermal bypass. Thermal bypass is is a term for places where heat is entering your home; these are essentially bald spots in the homes insulation or thermal envelope. You can reference the Thermal Bypass Checklist at the EPA/EnergyStar website. If you have a 2 story home please read section 4: Walls Adjoining Unconditioned Spaces.


Check attic ventilation. Radiant barrier will reduce the heat getting in, but you still need good airflow to help carry the heat out. Attic ventilation is very simple: holes in the top of your attic (i.e. wind turbines, static vents or attic fans – which consequently we do not recommend) and holes in the bottom of your attic (usually in the form of soffit vents) that are clear and open. You must have both! Air cannot move out unless it can move in from the bottom. Electric attic fans usually just suck the cold air out of your home, which is why we typically recommend passive systems for attic ventilation.


Windows that catch sunlight. We hate to tell you this, but windows, and especially west-facing windows, are a brutal source of heat gain. As a rule, a home’s heating/cooling bill is always directly proportional to the percentage of window surface area. The best windows have an R-Value of about 3 to 4. Even low-e double pane windows are a gap in the thermal envelope that allow heat to enter or escape. What can you do? If a window catches direct sunlight, then we recommend you invest in some solar screens or really good professional-grade window film (nano-ceramic window film) as it will make a huge difference.

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