HVAC Duct Overview

By | June 13, 2015


HVAC Duct installation
Installing air-conditioning equipment requires three crafts duct, electrical, mechanical, which includes refrigeration. Some contractors will separate crews to carry out the different tasks. While others may perform the duties of two crafts with their own company and subcontract the third to a more specialized contractor.
 
Some small contractors do all three jobs with a few highly skilled people.
 
The three job disciplines are often licensed at local and state levels and they may be licensed by different departments.
 
Square Rectangular Duct
Square metal duct is fabricated by a sheet metal shop by qualified sheet-metal layout and fabrication personnel. The duct then moves the job site and assembled to make a system. Because the all metal duct system is rigid, all dimensions have to be precise, or the job will not go together.
 
The duct must sometimes rise over objects or go beneath them and still measure out correctly so the takeoff will reach the correct location.
 
The branch duct must be the correct dimension for it to reach terminal point.
Square duct or rectangular duct is assembled with S fasteners and drive clips which make it duct connection nearly airtight and further ceiling is needed the connection can be taped. the tape special product called mastic may be applied to the duct joints with a stiff paintbrush.
It dries hard but is slightly pliable. It becomes an airtight connection for the air pressure within the duct. While the duct is being assembled it has to be fastened to the structure for support. This can be accomplished in several ways. It may lay flat in the attic insulation or be home by hanging straps.
 
Reduction can be done so that it will be steady when the fan starts and will not transmit noise to the structure.
 
The rush of air which has weight, pushes down on the duct and will move the duct if not fastened.
Vibration eliminators in the fan section will reduce the transmission of fan vibrations down on the duct.
 
Metal duct can be purchased in popular sizes from home supply houses for small medium systems this makes metal duct systems available to small contractor may not have a sheet-metal shop. The arm in a standard duct sizes can be assembled when the assortment standard fittings to a building that appeared to be custom-made for the job.
 
Round Metal Duct Systems
Round metal duct systems are easy to install and are available from some supply houses in standard sizes for small medium systems these systems use reduced fittings from the main trunk line and may be assembled in the field.
This type of system must be fastened together at all connections. Self tapping sheet-metal screws are popular fasteners. The screws are held by magnetic screw holders while an electric drill turns and starts to screw.
 
Each connection should have a minimum of three screws spaced evenly to keep the duck steady a good installer can fastened his connections as facet of the screws to replace in the screw holder. A reversible Cordless drill and I’ll deal tool to use.
 
Round metal duct work takes more clearance space than square rectangular ductwork.
 
It must be supported and mounted at the correct intervals to keep it straight. Expose round metal duct does not look as good as square duct and rectangular duct so is often used in places that are out of sight.
 
Insulation for Metal Ductwork
Insulation for metal duct can be applied to the inside or the outside of the duct. When installation is applied to the inside is usually done in a fabrication shop. The insulation can be fastened with tabs glue both. The tabs are fastened to the inside of the duct and have a shaft that looks like a now protruding from the duct.
 
The liner in the washer are pushed over the shaft. The tabs have a base to which the shaft is fastened to the inside of duct by gluing or spot welding. Modeling is the most permanent method that is difficult to do and expensive.
 
The liner is normally fiberglass and is coated on the air side to keep the airflow from striping the liner many pounds of air passes through the productive season. An average air conditioner system and how 48 ft.³ per minute of air.
 
Duct Board Systems
Fiberglass duct board is popular among many contractors because requires little special training to construct a system. Special knives can be used to fabricate the duct in the field. When knives are not available simple cuts and joints can be made with utility or contractors not. But this duct insulation is already attached to the outside skin. The skin is made of oil the fiber running through it to give it strength. When assembling the duct is important to cut some of the insulation away so that the outer skin can overlap surface that is joining. The two skins are strengthened to staple them together and tapping to make them airtight.
 
Fiberglas duct board can be made into almost any configuration that metal duct can be made into. It is lightweight and easy to transport because the duct can be cut layouts flat and assembled at the job site.
 
Metal duct fittings on the how other hand can take up a lot of space in a truck.
 
Original shipping boxes can these transfer the duct board and keep it dry.
 
Brown fiberglass duct is an easy to install as the duct board because it can be cut with a knife. The fiberglass duct can be supported like metal duct to keep it straight the way to ductwork itself positive side long stance.
 
Fiberglass duct deadens the sound because this inside the duct has been coated that helps the deaden of any fan noise that may be transmitted to the ductwork. The duct itself is not rigid does not carry sound.
 
Flexible duct
flexible duct has a flexible liner and may have fiberglass outer jacket for installation as needed. For example where a heat exchanger takes place between the air the duct and the space with the duct is routed. The outer jacket is held by moisture resistant cover made of fiber or vinyl. Duct may be used for the supply or the return and should be run to the direct path to keep the closing of the duct. Sharp bends can greatly reduce the airflow and should be avoided.
 
With used in the supply system flexible duct may be used to connect the main trunk to the boot of the room diffuser. The boot is the fitting that goes through before. In this case it has a round connection on the end for the flexible duct Rectangle or connection on the other end with the floor register fastened to it. The duct flexibility makes it valuable as a connector for metal duct systems. The metal duct can be installed close the boot in the flexible duct can be used to make the final construction. One runs a flexible duct are not recommended unless the frictional losses taken into account.
 
Flexible duct must be properly supported. A band 1 inch or more is the best method to keep the duct from collapsing and reduce the inside dimensions. So flexible duct has built-in eyelet holes for hanging the duct. Tight turn should be avoided to keep the duct collapsing on the inside and reduce the inside dimensions. Flexible duct should be stretched to a comfortably to keep the liner for closing a great friction.

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