The Jigsaw Puzzle Of Installing Ducts

Installing a A/c duct work in the house is no less than solving a three-dimensional puzzle. It has many things such as, studying the design of the house, calculation of duct size, and then designing a layout for duct run. However an efficient duct cleaner will bank on the natural flow of air while designing a duct work for the house. This is true for new duct work, a retrofit model, or adding duct work in a room of the house.

Let’s take look at the basic rules of laying network of ducts-

• According to the basic science of airflow warm air rises up as it is lighter. The cool air falls down. Therefore when duct work of air-conditioner is designed, the return ducts are installed high up on the wall. These will capture warm room air and send it to the central unit at the basement for cooling. Again the ducts that return stale air of the room to the furnace will be installed at a low point on the first floor, to capture cooled air and return it for heating. Registers delivering warm air should be in the floor or low on the wall; Registers providing cool air should be installed high up on the wall.

• The ducts that run from the basements to the registers in the upper floor should be made straight as far as possible. Too many turns will reduce the speed of the air. A vey less air will be delivered to the register.

• All the registers should be fed directly from the central unit. If the registers of the third and second floor are stacked together on a single duct then the air would go to second floor and a marginal amount would come to third floor.

• The layout of the duct run should be made clearly on paper before executing it. Ensure you have studs and bays of the house, lined up and aligned, providing a clear path for the ducts to run through them.

• Use appropriate fittings at the turns so that velocity of the air does not come down. Some bends are necessary, but they can cause restrictions which reduce airflow. If there is need for a 90-degree bend, it is better to go for two 45-degree bends. However there should be space for it. This will make it easy for the air to flow without any back pressure.

• The duct running though unconditioned spaces such as attics, basements crawl spaces should be well insulated to prevent leakage of air to the surrounding.

• It is always wise to begin the installation of the duct from the air handler to outward. The trunk is installed with necessary transitions from one size to other. The duct boards made of fiberglass comes with a system of S-cleats and drives. The S-cleats are used to connect the tops and bottoms of the ducts together and lock them at places. The cap is fitted at the end of the duct unless it would branch into smaller ducts. The metal ducts are fitted together with slip fitting. The adjacent ducts are fitted with short drill-point sheet metal screws.

• To allow the main duct to branch into smaller ones holes are cut into the sides of the trunk. The cross-section could be round or rectangular. A rectangular section is cut if the branch ducts need to go to several registers. When flexible duct work is used as branch ducts, the hole is always round.

• The next task is to connect the branch duct to the main trunk. This is done with a metal joining collar. The collar has tabs to attach itself with trunk. The branching duct slips over this joiner and gets connected to the trunk.

• A flexible duct run is secured in place with large plastic cables. All duct joints are sealed with mastic and tapes.

• The registers box is attached to the duct at the room end. A register box is connected to the duct at one end and the register at the other. It is connected to the studs and drywall with a flange. The latter also keep it joined to the register.



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