Instructions / Assembly

ManualsBrandsSpeedi-Products ManualsDucting & Venting14 in. x 10 in. Galvanized Sheet Metal Three Piece Reducers

Ductwork

After studying this chapter, you will be able to:

• Explain operation of the supply and return air duct

systems.

LJ Assemble, join, install, and repair all types of duct.

^1 Tnstail registers, diffusers, and grilles.

^| Insulate and properly support piping.

• Explain why and how to use mastic and fiberglass

membrane.

• Name and describe the use of many types of fittings.

Important Terms

A-coil

bonnet

branch lines

cfm

conventional system

diffusers

downflow furnace

drive cleats

ductboard

extended plenum

fiberglass membrane

forced air

horizontal furnace

insulated flexible duct

mastic

perimeter system

plenum

radial system

registers

return air

scrim

S-hooks

starting collar

supply air

takeoff

trunk line

U-channels

upflow furnace

vapor barrier

The information contained in this chapter provides

the knowledge needed to working with heating and air

conditioning ductwork. Some sizing information is

presented as simplified "rules of thumb," consistent with

practices in the field, rather than becoming involved

with complex formulas. While the illustrations in this

chapter show typical situations, keep in mind that

adaptation to conform with state and local codes may

be necessary.

28.1 Forced Air Systems

The majority of heating and cooling systems are

classified as "forced air" types. Central heating and

cooling involves the use of one furnace, centrally

located in the structure, that is equipped with a motor

driven fan to blow treated air through a ductwork system

to the living spaces. Basic components of a forced air

system arc a furnace unit, a remote air conditioner

(compressor/condenser unit), ductwork, Figure 28-1,

and registers (outlet devices that direct and usually

control the volume of the airflow). The ductwork

consists of separate "supply air" and "return air"

sections. The supply air section is used to distribute

treated air to living spaces, while the return air section

brings air from the living spaces back to the furnace

unit to be heated or cooled again.

28.1.1 Conventional System

Before the development of forced-air systems,

gravity furnaces were used. These furnaces had to be

located centrally, with short runs of ductwork from the

furnace to the air outlets. All supply air outlets were

located in or near inside walls of rooms. Return air

inlets were generally located in or near the baseboards of

outer walls. For a period of time after they were intro-

duced, forced-air systems were similarly designed, and

many existing houses have this type of system. Such

an arrangement, with inner wall-located outlets and

outer wall-located inlets, is called a conventional

system.

Summary of content (24 pages)

PAGE 1
Ductwork After studying this chapter, you will be able to: • Explain operation of the supply and return air duct systems. LJ Assemble, join, install, and repair all types of duct. ^1 Tnstail registers, diffusers, and grilles. ^| Insulate and properly support piping. • Explain why and how to use mastic and fiberglass membrane. • Name and describe the use of many types of fittings.
PAGE 2
Heating and Cooling Essentials sufficient and uniform air circulation for maximum comfort. 28.2 Furnace Classifications All forced air furnaces are classified according to the direction of the airflow for Ihe supply air. The upflow and downflow furnaces are most common, but horizontalflow models are necessary for some applications. Figure 28-1. Installing an air duct system may be a part of your job in either new construction or remodeling work. 28.1.
PAGE 3
Chapter 28 Ductwork Flue or vent Air filter or electronic air cleaner Figure 28-3. An upflow furnace has a top-mounted plenum to distribute supply air. Upflow units are typically located in a basement. home, Figure 28-4. The air conditioning evaporator coil is mounted on the bottom of the furnace, inside the plenum. Supply air travels from the plenum through ductwork to the living spaces. Return air enters the top of the furnace. The blower serves for both heating and air conditioning. 28.2.
PAGE 4
Heating and Cooling Essentials Extended plenum Figure 28-4. In a mobile home, or a building with a crawl space instead of a basement the downflow furnace is commonly installed. The plenum is below the unit. 'Air filter Flue Figure 28-5. A horizontal furnace is usually located in an attic or a crawl space.
PAGE 5
Chapter 28 Ductwork A-coil Supply air Slant coil ^ Supply air Supply air Liquid line Liquid tine Suction Condensate catch pan Condensate catch pan Condensate drain Equalizer Suction Return air Return air Condensate drain Upright coil Liquid line Supply air Condensate catch pan Suction Condensate drain Figure 28-6. The three types of air conditioning evaporators. In residential installations, the A-coii type is most commonly used.
PAGE 6
Heating and Cooling Essentials Branch piping Register boot Plenum Side takeoff Furnace Extended plenum Figure 28-8. Round branch piping extends outward from an extended pienum formed with rectangular duct. 28.4 Distribution System Components-^ 28.4.1 Plenum (Bonnet) The "supply air" distribution system includes the plenum, the main trunk line, and all the branches serving different living spaces. Each branch terminates in a register that directs and usually controls the volume of the airflow.
PAGE 7
Chapter 28 Ductwork evaporator is located inside the plenum, Figure 28-9B, and the supply air duct attaches to the plenum. The furnace manufacturer offers a plenum kit along with the necessary evaporator. For adding air conditioning to a previously installed furnace, some sheet metal work may be required. After all parts are assembled and screwed together, the seams must be anchored with .
PAGE 8
Heating and Cooling Essentials 28.4.4 Insulated Flexible Duct As shown in Figure 28-13, insulated flexible duct consists of several layers, each with a specific function. The core is usually two plies of polyester film used to encapsulate the galvanized steel wire helix. The purpose of the wire helix is to help flexible duct keep its shape. The insulation is a fiberglass blanket, varying in thickness, depending on the R-valuc.
PAGE 9
Chapter 28 Ductwork used for extended plenums is 30-gauge, galvanized sheet metal, 8" deep, 60" long, and comes in standard widths of 10", 14", 18", 24" and 28". One of these standard sizes should provide the needed capacity, but any length of duct can be cut to a shorter length. 6" pipes 28.5.2 Rule of Thumb for Determining Plenum Size To determine the width required for an extended plenum, counl the number of round pipes it will serve, Figure 28-16.
PAGE 10
Heating and Cooling Essentials Straight cut Pipe size (diameter Avg. cfm @ Static pressure 4" 30 cfm 5" 65 cfm 6" 110 cfm 7" 160 cfm 8" 230 cfm 10" 410 cfm 12" 680 cfm 14" 1000 cfm 28.5.4 Provide Adequate Airflow A furnace located in a small utility room or closet may not receive a sufficient amount of air for proper combustion. If the furnace room is closed off, provide an adequate air supply by installing two grilles in a door or wall facing a well-ventilated area, Figure 28-17.
PAGE 11
Chapter 28 Ductwork battery operated drill, chisel, gloves, lineman's pliers, diagonal cutters, and longnose pliers. NOTE: Aviation snips are used for cutting openings in sheet metal. Never use them to cut wire. 28.7 How to Lay out a Duct System —# The heating and cooling units should be matched to the square footage of the building's floor space.
PAGE 12
Heating and Cooling Essentials Takeoff Figure 28-22. Top of the takeoff should be located 6" below the top of the plenum. To install the takeoff, first mark off the proper size opening. Next, pieree the metal surface using a drill or sharp tool and cut the opening with snips. Then, insert the takeoff into the opening, and fold the tabs down inside. Finally, secure the takeoff with three sheet metal screws and seal it with mastic. 28.9 Working with Round Metal P i p e - * Figure 28-20.
PAGE 13
Chapter 28 Ductwork 28.9.1 Joining Pipe Lengths 28.9.2 Cutting Round Pipe Each pipe length has a plain end and a crimped end. Lengths are joined by sliding the plain end of one length over the crimped end of another length. Line up seams for best appearance and push lengths together for a tight joint. Fittings are made similarly. The crimped ends always point in the direction of airflow. Secure each joint with three drive screws evenly spaced around the joint and seal with mastic. See Figure 28-24.
PAGE 14
Heating and Cooling Essentials Adjustable Elbow 90° 45° Figure 28-27. After securing the collar with sheet metal screws, seal the collar with membrane and mastic. This prevents leaks due to vibration. Cutting slits in the membrane will help it lie flat. Figure 28-26. Adjustable elbows are convenient for making all types of turns. They are available in all round duct sizes. flat, use a utility knife, to make a series of slices about every two inches along its edge.
PAGE 15
Chapter 28 Ductwork Figure 28-30. Use a ball pein hammer on each seam for a tight fit. S-hook A B C Figure 28-29. How to assemble rectangular duct. A—Match the ends of the two half sections. B—Start the edge channels. C—Slide the two sections together. To form a length, place the two half sections on the floor with the "S-hook" ends up. Pick up one piece and engage its edge channels with the channels on the other piece, then slide the two together.
PAGE 16
Heating and Cooling Essentials Figure 28-33. Installing a top-mounted takeoff. A—Draw the outline for the opening. B—Punch a hole to use when starting the cutting snips. C—Cut around the outline. starting collar or takeoff is used. Make a template of the opening required and draw its outline accurately on the metal to be cut, Figure 28-33A. Punch a hole through the sheet metal within limits of the opening, using a hammer and chisel or similar tool, Figure 28-33B.
PAGE 17
Chapter 28 Ductwork Keep pipes at least one inch from joists and other combustible material. To prevent heat loss, metal duct is often wrapped with insulation, Figure 28-36. If insulating material is appl ied after the duct is already in place, the insulation will have to be slit or stripped to get around the supporting strap or wire. This opening must be rescalcd to maintain insulating effectiveness. Insulation Pipe Strapping Figure 28-37.
PAGE 18
Heating and Cooling Essentials 4" metal sleeve D Figure 28-39. Connecting lengths of insulated flexible duct. A—Cut completely around and through duct with knife or scissors. Cut wire helix with heavy-duty snips or side cutters. B—Peel back the jacket and insulation from core. Butt two cores together on a standard 4" metal sleeve . C—Tape core together with at least two wraps of duct tape. Secure with two approved clamps. D—Pull jacket and insulation back over cores.
PAGE 19
Chapter 28 Ductwork 2 1 /4" 3 1 /4" Wall stack Boot 8" pipe Boot 6" pipe Figure 28-42. Wall stack duct is designed to fit between the studs inside a wall. Different sizes include 2-1/4" or 3-1/4" deep by 10", 12" or 14" wide. Standard length of a stack section is 24". through registers or diffusers. Both have dampers or vanes for controlling the amount of air, but diffusers also have adjustable vanes for controlling the direction of discharged air.
PAGE 20
Heating and Cooling Essentials Figure 28-44. Preparing to cut a floor diffuser opening. A—Measure and trace the opening for the diffuser. B—Drill a centered hole through floor. C—Check clearances from below. Figure 28-45. installing a floor diffuser. A—Cut along the outline with a jigsaw, circular, or reciprocating saw. B—Secure the register box (boot) to floor with nails. C—Install the floor diffuser into boot opening and secure it with screws. 28.
PAGE 21
Chapter 28 Ductwork floor plate can be cut from below the floor. Using the stud space as a return-air duct requires sealing off the stud space just above the grille opening with a 2" x 4" wood block as shown in Figure 28-49. Installing floor type or baseboard type grilles is much the same as installing supply air registers in those surfaces, Figure 28-50. Floor type and baseboard grilles require larger holes than diffusers. Figure 28-47.
PAGE 22
Heating and Cooling Essentials Temporary support wire Floor opening to joist spaces Tape Insulation Figure 28-52. Use tape or sealant to close insulation on round pipe. Remove temporary support wires and replace them with strapping. Ducts in homes with high energy-efficiency ratings are usually sealed with mastic and fiberglass reinforcing membrane, Figure 28-53. Mastic is a nontoxic adhesive-material used for permanently sealing joints and seams for all types of air duct materials.
PAGE 23
Chapter 28 Ductwork mastic is water-based, nonflammable, fiber-reinforced, fast drying, and waterproof. Easy application, and clean-up with soap and water are attractive features of the material. Mastic can be applied by brush, trowel, caulking gun, or with a gloved hand. It typically dries to touch in 1 or 2 hours, but unusually wet conditions may require 4-5 hours drying time. Insulation can be installed over mastic that is still wet, but care is needed to prevent excessive movement and loss of seal.
PAGE 24
Heating and Cooling Essentials radial and extended plenum, are described in detail. "Rules of thumb" are provided for sizing a duct system for efficient airflow. Detailed information on laying out and fabricating duct systems is provided, and covers the major types of duct materials: rectangular metal duct, round metal duct, and insulated flexible duct. Directions are given for installation of wall stacks, supply air registers/diffusers, and return air grilles.