The subject of repairing or replacing your ductwork may come up if you're trying to increase your furnace's efficiency, if you're worried that there is any damage, or if you are trying to improve the air quality in your home. Even if your home is only a few years old, certain circumstances may require the attention of professionals. The primary factor in whether you should clean or replace your ductwork is the severity of the problem you are experiencing.
Poor Air Quality
If your ducts are revealed to be the source of poor air quality in your home, a professional may recommend cleaning and repairs if there are any gaps letting in large amounts of dust or debris. This may also be necessary if there is any mold growth in the ducts, which can spread spores into every room. In most cases, a standard cleaning should suffice, but there are a few exceptions. The first exception is the material of the ductwork. Some duct lining materials are not easily cleaned, and the cost to clean them would be comparable to replacing the affected areas. The second exception is if the debris or mold contamination is so severe that a cleaning would not properly get rid of it.
It's a given that some hot air will be lost through holes in your ductwork—it's just a matter of how much. Once it gets to a certain level—say, 20 percent heat loss—you may consider repairs to patch some of the holes and breaks in the ducts. If you have ductwork that is decades old, it may be tempting to simply replace it all, but this isn't necessarily the best option. For example, switching from old metal ductwork to flex ductwork doesn't guarantee an increase in efficiency.
Replacement is a safe choice if any damage to the ductwork is severe, or if repairs would necessitate working on most of the ductwork in your home anyway. Otherwise, repairs may be a better option, even with old ductwork. The key is in how these repairs are done. For example, rather than simply using tape to reseal the ducts, use a mastic product instead. This will do much more to increase your furnace's efficiency.
Poorly Maintained or Dirty Ducts
If your furnace is properly maintained, you can go years without needing to clean your ducts or perform any repairs. If you have let this maintenance slip, or if you have purchased a house where the system was not adequately maintained, the ductwork should at the very least be inspected. The effectiveness of cleaning on certain problems, like layers of gunk or debris from smoking, pets, or home renovations, can start to lessen depending on how long it has been allowed to build up, but let a contractor make this determination. In most cases a cleaning service will be adequate to fix the problem. Replacement should only be necessary if there is a contaminant the cleaning service cannot get rid of or if there is additional damage.
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