There are three basic components to a standard heating and air conditioning system:
Ductwork is the all-encompassing term for the system of runs that carry the conditioned air (either heated or cooled) from the air handler or furnace to specific rooms in your home. For most people, it’s out-of-sight, out-of-mind since it’s usually located in the attic or the crawlspace, neither of which are popular hang-out joints. But sometimes the reason you may feel more airflow in one room than another, have no airflow in one room, or even smell something foul isn’t always because there’s something wrong with your equipment. There could be something wrong with your ductwork.
Ductwork construction materials are defined by the NC Building Code. Most systems are metal, ductboard, and/or flexible duct (or flex).
Metal – It’s almost always galvanized steel. It is usually round pipe or square or rectangular-shaped made from a sheet of metal. It is used to build the supply and return boxes (plenums) that connect to the indoor unit, and the trunks, or main lines, that come off the plenums. If it’s located in an unconditioned area like a crawlspace, it should be wrapped with insulation. Sometimes it’s lined with insulation on the inside. If you knock on it gently, you should be able to tell.
The disadvantage is that it is a little more expensive. It takes special skills to build metal ductwork and can take a little longer to install properly which contribute to the higher cost. But because of its many benefits, we here at Canella Heating and Air Conditioning use metal almost exclusively for our plenums and trunks.
Ductboard – This product is made from tightly compressed glass fibers (fiberglass) that are bound together with a sealing agent. Like metal, it is used to build trunks and return boxes. It doesn’t require insulation over it because it is insulation.
The advantage to ductboard is that it’s less expensive than metal. The disadvantages are:
Flex – Flexible duct is round and consists of a plastic liner with a layer of insulation surrounding it. Its name suggests its most important feature: it’s flexible and can bend around things like floor joists and plumbing pipes. It is used to carry the air from the main trunk to a register in a specific room. It comes in different sizes depending on how much airflow is needed for a particular room and the length of the line, among other things. Because of how it’s constructed, it’s rougher on the inside than metal and does offer some resistance to air flow. The good news is that it’s cheaper than ductboard or metal and can easily be replaced when necessary.
Over time things happen to ductwork. Humidity, bumping into it with things you store in the basement or attic, animals, or poor installation practices are all things that can damage ductwork and cause leaks or a complete disconnection of the duct from the system. Now the air you’re paying to heat or cool isn’t making it to the room you think it’s going to and in fact is being wasted by dumping into your crawlspace or attic.
Another common sight is ductwork that has been crushed or pinched off. This reduces the airflow, tends to make the airflow noisier, and can cause static pressure issues that bring a whole host of their own problems. You’ll feel it in the form of temperature differences between rooms.
Technically its “microbial growth” until it’s actually tested by a lab and confirmed to be mold. Whatever you want to call it, you know what it looks like. Under the right conditions it can grow inside ductwork or even the equipment itself. When you turn on the heat or the air conditioning, the air passes right over the mold and carries it through the rest of the system into your house. This can contribute to health issues for those with allergies, asthma or other respiratory problems.
Insulation around ductwork does two things: it helps keep the air inside the duct either hot or cold until it reaches the room it’s supposed to go to, and it keeps ductwork from sweating. Sweating ductwork, which happens when it’s humid outside and the air inside the duct is cold or vice versa, doesn’t sound too serious but it can make a mess. If the ductwork is in the attic and enough condensation forms, it can start to leak through your ceiling. And in your crawlspace or basement, moisture is one of the 3 things mold needs to start growing (besides a food source and heat).
Size does matter. If your bedroom is 15 feet away from the air handler and you have a 4-inch duct that runs to that room, it will carry much less air than a 10-inch duct can carry. That will directly affect how much hot or cold air makes it to your bedroom. This is why it’s just as important for an HVAC contractor to correctly size the ducts as it is to correctly size the equipment. Too small and you won’t get enough hot or cold air. Too large and too much air will get to your room again making it either too hot or too cold and short-changing another room in your house.
This only begins to explain the science behind ductwork and what can go wrong. Looked pretty simple before you read this, didn’t it? Understanding what’s going on with your ductwork, whether it’s installed correctly, and whether it’s working like it should is a job only a qualified HVAC contractor can do.
We have the tools to show you what’s going on including cameras that can take pictures inside the ductwork. And if it’s bad, we have the expertise to fix it.