Furnace ductwork can come in many sizes, and choosing the correct size can affect many different factors of a heating system. Here are three reasons to decrease the size of the ducting coming from a furnace:
1 - Price
Many industrial ducting systems try to reduce their ducting systems to the smallest size possible that will still efficiently heat their buildings. The reason for this is simple: smaller ducting costs less because it uses fewer raw materials than larger ducting does. Therefore, reducing ducting from the main trunk line to smaller ducting may help keep the cost of the heating system down. Beware though, reducing the size of the ducting too much will result in the air-speed velocity within the ducts to become too fast. This may cause problems with the pressure within the system.
2 - Increase Air Velocity
By reducing the size of a duct, the air traveling within it will begin to speed up exactly like water does when a person puts a finger over the nozzle of a hose. The result is that more air will flow through the system in a shorter period of time, and the air that comes out of the vents will travel further across the room it is cooling. However, as mentioned above, too much air speed can be a bad thing. It can cause noisy rattling in the ductwork as well as large pressure drops in the main line that the furnace fan may not be able to cope with. It is important when reducing the ducting to not reduce it too much.
3 -Space Restrictions and Wyes
Sometimes with all the inner workings of a building in the way like walls, plumbing, supports, etc., one must reduce the size of a ductwork just to make it fit through a specific area. In addition, in order to make a ducting travel in a specific direction, a person will have to use a wye connection. A wye is a fitting that has a branch coming away from it at a forty-five degree angle, like the letter, “Y.” These fittings, while useful for branching a line in a certain direction, usually always will reduce the size of the ducting, since the branch on the fitting itself is almost always smaller.