A Few Things To Know About Duct Leakage

Wastage of energy in the house makes deep holes in your pocket. There are quite a few scopes of energy wastage in every house. Leaky A/c ducts are one of them. According to researchers at Lawrence Berkeley National Lab on an average about 10% of air leaks from supply ducts and about 12% from the return air ducts.

Air can leak out from ducts for various reasons. The duct itself could have developed holes with insulation in very bad shape. As a result the air leaks out through these into the exterior environment. The joints of the ducts are one of the most vulnerable areas which allow seepage of air. However you should remember one important fact in this regard. If the ducts are leaking in the conditioned spaces of the building then it is not bad. This is because the leaking air is cooling or warming an airtight space. But if it leaking in the unconditioned spaces such as crawl spaces, basements, or attic then then you are really flushing your money into the toilets.

Besides the leakage itself, the location of the leakage also makes a difference. The leakages can be found in both return and supply ducts. Supposedly, if all the leakages are all on the return ducts that run through unconditioned space and pull in unconditioned air, it will create an imbalance in the house pressure. Let’s substantiate this with numerals. You ducts are putting in 900 cubic feet per minute (cfm) of air through supply duct which has no leakages. However the return duct has leak through which it pulls in 100 cfm of air from the unconditioned attic.

So 900 cfm of air is going through the air handler, the return duct has to pull 800 cfm from the house. This creates positive pressure in the house which is bad for the health of your HVAC. It reduces airflow through your HVAC. Moreover the house will never get that 900 CFM of air through the non-leaky supply ducts as the blower will not be able to push that much air against the pressure inside the house.

Now if the leakages are on the supply ducts then it will generate negative pressure in the house and more infiltration. This will also reduce the airflow.

Therefore leakages in the duct not only cause sheer wastage of energy but are also bad for the health of you HVAC. So monitor your ducts from time to time for leaks. If you suspect leaks in the duct, call a duct repair service to conduct tests to detect leakages and seal them with appropriate ways. The joints of the ducts are one of the potential areas of the duct that cause a substantial volume of air to leak out. Here are some tips to make duct-joints foolproof--

• The seams of the ducts should be fastened mechanically. Sheet-metal screws can be used for galvanized ducts and compression straps for flex duct.

• If the diameter of the galvanized duct is of 12 inches or lower than 3 screws should be used per joint. To secure ducts over 12 inches in diameter, five screws are needed per joint.

• In rectangular galvanized ducts one screw should be used at each side.

• Always use mastic instead of tape. The layer of the mastic should be as thick as nickel. Duct tapes cannot withstand temperature fluctuations that often happen in ducts. Therefore they will not last beyond a short period.

• The seams wider than 1/16 or 1/8 inches should be mended with fiberglass mesh as well as mastic.

• The collar connections between plenums and duct take-offs should be sealed well.

Sealing joints in flex duct:

• The joints of flex duct should be connected with a beaded metal sleeve or coupling. The duct boot should be inserted at least 3 inches at the end of the duct. It should be attached to the inner sleeve of the flex duct with clamp or screws. Thereafter duct tape and mastic should be used to reinforce it.




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