How to seal your ducts

Your duct leakage can account for up to 20% of your leakage in your home. This is considerable amount in itself but is even more of a concern when you consider that in most homes the majority of the ducts are located outside of the conditioned space in the attic or crawlspace. The leakage into these spaces is costly and can create unwanted pressure differences in the home.

Locating the Leaks

The first step in eliminating the leaks in your duct work is to find them. This can be done in several ways but some are easier than others.

1. Visual inspection: All steps in finding the leaks will involve this process. You need to visually inspect the ducts to find any visible separations, penetrations or dislocations in the ducts. Some may be obvious while others may be hidden. Look for areas where duck tape may be failing (yes is it duck and no it should not be used to seal duct joints.), at locations where two ducts meet, around the boots in the floor or ceiling and at the trunk line.

2. Duct blaster: You can have a professional perform a duct blaster test on your duct work. This will let you know how much leakage is in the duct work but by itself it does not tell you where the leaks are. You can however have the professional use theatrical smoke to fog your duct work. This will allow you to see where the leaks are as the smoke will exit at the leaks.

3. Panning: Again a professional is needed for this. A professional will use a blower door and a pan to test your ducts to see which ones are leakier. This method can help isolate problem ducts but it does not have the ability to locate the leak itself.

Fixing the leaks

Once you have located the leaks you need to fix them. First you need a few supplies. These are:

1. Mastic- a material used to seal the ducts
2. Cheep paint brush-used to apply the mastic
3. Fiberglass tape-used with the mastic to seal the joints
4. Large zip ties- used to secure the inner and outer layers of the duct work
5. Duct-you may need to replace torn sections.

Duct Joints:

If you have leaks at the joints of the duct work you will need to seal these joints with mastic. This will be where the majority of your leaks are so this is the most common fix. First remove any old tape form the joint and then remove the outer layer of the duct. This is if you have a flex duct. If the inner plastic layer of your ducts is not secure you can use a zip tie to secure the inner duct. Next apply a large helping of mastic to the inner layer of the duct. You can then slip the outer layer back over the duct. Some individuals like to also secure the outer layer as well using the zip ties. You will then mastic the outer layer as well using the same technique you used on the inner layer. Make sure you pull the insulation (outer layer) over any boots or collars.

Disconnected Ducts:

If you have any fallen or disconnected duct work you will reconnect the duct work in the same manner as described in the above step.

Metal ducts:

This covers both the metal supply ducts and trunk lines. You will follow similar steps as in the duct joints section however you will use metal sheet screws to secure the duct if needed. Also you may have some gaps larger than ¼” and will need to use the fiberglass tape along with the mastic.

Torn ducts:

Unfortunately flexible duct work will tear. If this happens you may not be able to repair the duct and will need to replace the whole run or just a section. If you are repairing just a section make sure you use metal joints at both ends of the patch and use the same techniques as in the duct joint section.

Alternative methods:

There are alternative products and methods to sealing your duct work. These include mastic tape and foil tape. Mastic and mastic tape is best used on duct work but foil tape can be used to seal items that need to be routinely opened like your air handler.

There is also an alternative method of sealing that a professional can do. This involves spraying an adhesive/sealant through the duct work. The sealant finds its way into the leaks and seals anything up to a ¼”. This can be a cost effective way to seal the duct work if you have several small holes.

Don’t “crank” your dial on your thermostat.

Moving the temperature setting higher up on your thermostat does not make you home heat up any quicker. If you have a heat pump move your thermostat 2 degrees at a time to help conserve energy. If the thermostat setting is raised greatly the heat pump will use your heating strips to heat the home costing you a lot of money.

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