This method statement of HVAC Duct (Heating, Ventilation, and Air Conditioning) system installation details the various procedures for the installation of HVAC ducts and accessories, return and exhaust ducts, balancing dampers, fire dampers, and access doors. The purpose of the installation method statement is to define the implementation in conjunction with relevant ITP, health, safety & environment (HSE) requirements outlining the responsibility and quality verification of work.
Table of Contents
Scope of Work
Pre-installation
All workers shall attend safety induction training conducted by the contractor and be given specific training on the safe installation method used.
Ensure that the material to be used is inspected and approved.
Ensure that all accessories installation is as per SMACNA Standards (Sheet Metal and Air Conditioning Contractors’ National Association). Accepted engineering practice and data, such as that found in the four ASHRAE handbooks and the SMACNA HVAC duct system design manual, should be used to design systems. (However, SMACNA does encourage the development and use of new technology and it invites authorities to consider alternative construction methods.)
Ensure that approved materials required to carry out work will be available. All working areas where possible will require signage and barriers.
Prior to the commencement of work, areas, and access will be inspected to confirm that the site is ready and safe to commence the work.
All relevant documentation and material applicable to a particular section of work will be checked by the Site Engineer / Supervisor before the commencement of work. All documentation shall have a copy fixed on the project (Material inspection, etc.). For fire-rated air conditioning ducting: all ductwork shall come with documents describing the product’s fire rating. Each duct system must be built to meet the duct pressure classifications specified on the contract drawings.
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Ensure proper storing/handling of the ducts without damaging the surface. All ducts will require open ends to be sealed prior to delivery. Exterior duct sealant treatment should consist of applying products marketed specifically as forming a positive airtight and watertight seal, bonding well to the metal involved, remaining watertight with metal movement, and having a service temperature range of -30°f (-34°c) to 175°f (79°c).
Check all the ductwork is pre-fabricated with tag number labeled and received at the site in accordance with specifications and correct dimensions as per approved drawings,
The Site Engineer / Supervisor will give the necessary instructions to the tradesmen and provide necessary approved construction / approved shop drawings to avoid wrong connections during assembly or installation.
The Site Engineer / Supervisor will also check that the tools and equipment available are in compliance with contract requirements. Check all tests are being carried out where required Portable Appliance Testing (PAT) before being used to ensure they are fit.
General Requirements
This method statement of HVAC covers the installation of HVAC ducts and accessories at the site. The majority of the duct shall be pre-fabricated off-site either by the contractor or from an outsourcing company. Fabrication on site shall be minimal but a fabrication workshop shall be on site.
Pre-qualification documents for such facilities used for duct fabrication will be submitted to the Consultant for approval. All the relevant information (e.g. Location of the fabrication shop, production capacity, type of machinery, quality systems, the method used for communication, transportation of materials, etc. will be included in the pre-qualification document.
Approved and coordinated ducting shop drawings will be provided to the fabrication workshop for tagging, and the tagging list will be reviewed subsequently by the construction engineer.
Each section, such as ahu, outdoor air (oa), supply air (sa), return air (ra), and exhaust air (ea), should be clearly labeled with arrows indicating the proper flow directions.
Delivery of fabricated ducts to the site will be coordinated with the construction program to avoid storing ducts at site stores for long periods. The duct delivered shall have the openings covered by polyethylene at all times until site installation to prevent dust from accumulating on the inside surface.
A copy of this approved construction installation method statement of HVAC along with the relevant specification sheets from the contract document will be forwarded to the fabrication workshop to ensure the quality of ductwork fabrication meets the contract requirements.
A proper lifting machine is to be used and the operator is well trained & knowledgeable of procedural installation for all duct load to be loaded on the lifting machine.
Train the owner’s/client’s maintenance staff for operation and preventative maintenance as per project specifications.
Installation of Duct Horizontal Run
Scaffolding shall be assembled by competent personnel according to the height at which installation shall take place. All safety requirements shall be met as per the requirements in the Risk Assessment prepared by HSE Department.
Mark the route of the duct on the soffit of the slabs and non-fire-rated walls. Ensure that slabs and non-fire-rated walls and floors are free from damage and ingress of moisture.
Determine the position of support as per the approved construction drawing, coordinate layouts, and specifications and fix the supports using anchor bolts and ensure that all fixings (threaded rods, angles, clamps, etc.) are straight and secure. Any cut edges of angles, channels, or threaded rods will be painted with touch-up with zinc-rich paint. Adequate supports are to be provided before and after fittings, bends, offsets, etc.
Prepare and fix the duct supports as per the approved construction drawing and specifications. Using either self-drilling anchors or an appropriate size masonry drill, carry out the preparatory works in the slab to receive the anchors. Consider the anchor manufacturer’s recommendations for the diameter and depth of the hole.
Fix the anchors and ensure that they are adequately supported on either side. Hang the threaded rod and use lock nuts and washers to lock it with the slab. Remove the sharp corners at the open end of the GI threaded rod and angles. Fix the angle with a lock nut and a nut below. Load test shall be carried out prior to fixing.
Use only undamaged rust-free bolts nuts and washers in joining flanges together and tightening bolts.
Transport the duct pieces and fittings to the final location. Pre-assemble, (where ever possible) the duct pieces and fittings as per the approved shop drawing ensuring the horizontal and vertical alignment.
For large-size ducts, it shall be delivered to the site in sections and assembled on-site. A manual duct lifter, trolley, or movable pallet shall be utilized in the transporting and lifting of ducts whenever space/location permits. If not possible, duct pieces shall be transported manually. Lifting of duct materials to the rooftop shall be done using a tower crane. All necessary permits shall be issued before the execution of any works.
All known branches and tapping for collar/flexible etc. may be done during the assembly stage.
Lifting of the duct onto the supports ensuring that each length is aligned and leveled with the preceding length as per dimensions shown on approved shop drawings. Ensure that all supports are properly loaded and adequately padded with load-bearing material.
Approved duct sealant shall be applied to the joints. Any excess sealant shall be removed so that the joint is left in a clean and tidy condition. Use only undamaged bolts nuts and washers to join mating flanges together and tighten bolts.
Ensure that ductwork is clean and no construction debris exists within the ductwork before proceeding to the next length. Permit required for the sealant. COSHH assessment to be carried out.
All open ends of the cleaned duct works shall be temporarily closed with polythene sheets before leaving the job site to prevent the ingress of moisture and dirt.
Ensure that all accessories such as silencers, volume control dampers, balancing dampers, fire dampers, access doors, test points, sensors, and associated plant equipment are installed in accordance with approved shop drawings. Make certain that the installed units are free from damage.
Install sound attenuation equipment and suitable materials according to approved shop drawings and HVAC installation method statement.
Installation of duct complete with accessories shall be checked & inspected before applying thermal insulation sheets at ductwork joints.
Ducts that are interrupted at the curb should be flashed to divert water over the curb or overhang the top of the curb.
Locate ductwork runs, unless otherwise indicated in the detailed shop drawings through horizontal and vertical checking, and avoid diagonal runs wherever possible.
If the AC duct is greater than 1.2 m in length, then ensure to support a separate bracket under the connected duct, and from it, a hanger-wire can be suspended for ceiling installation.
All high-level cutting, etc should be kept to a minimum.
Ductworks penetrating through external walls and floors shall be sealed to the wall.
See Also: AC Duct Cleaning Method Statement Recommended for HVAC Ducts and Accessories
Installation of Vertical Risers
The procedures are similar to the horizontal ducts. The following points have to be taken care of in duct riser installation:
Install duct support on the shaft as per the latest approved shop drawings.
Duct pieces shaft be pre-assembled / insulated before taking to the final location depending on the available space. If not possible to distribute duct pieces on floors, transport duct pieces to the roof or topmost portion of the building using available lifting equipment (tower crane as per coordination utilized in the transporting and lifting of ducts whenever space/location permits. If not possible, duct pieces shall be transported manually. Lifting of duct materials to the rooftop shall be done using a tower crane. All necessary permits shall be issued before the commencement of any works.
All known branches and tapping for collar/flexible etc. may be cut during the assembly stage.
Lifting of the HVAC duct onto the supports ensuring that each length is aligned and leveled with the preceding length as per dimensions shown on approved shop drawings.
Ensure that all supports are properly loaded & adequately padded with load-bearing material.
Approved duct sealant shall be applied to the connected joints. Any excess sealant shall be removed so that the joint is left in a clean and tidy condition.
Ensure that ductwork is clean and no tools/ construction debris exists within the ductwork before proceeding to the next length. COSHH assessment to be carried out.
All open ends of the ductwork shall be temporarily closed with polythene sheets before leaving the job site to prevent ingress of moisture.
Ensure that all accessories such as silencers, volume control dampers, balancing dampers, fire dampers, access doors, test points, and sensors are installed in accordance with approved shop drawings.
Install sound attenuation equipment and suitable materials according to approved shop drawings.
Installation of ductwork complete with accessories shall be checked & inspected before applying thermal insulation at ductwork joints.
All high-level cutting, etc. should be kept to a minimum.
Installations of Grilles and Diffusers
Check the location of grilles and/or diffusers if properly coordinated with light fixtures as per the approved reflected ceiling plan.
If grilles or diffusers are for unducted return air, ensure that the wooden/steel frame is in place provided by others. Make sure that the frame is properly supported and not sagging. Check ceiling level when installing the grilles or diffusers.
Fix the grilles collar securely to the wooden/steel frame with screws and seal the gaps with sealant. Install the removable face to the assembly.
If grilles or diffusers are for a ducted system, make sure that the plenum box or duct drops are in the correct location as per the approved shop drawings and elevation as per ceiling requirements.
Fix the grilles collar securely to the plenum box or duct drop by metal crews and seal the gaps with sealant. Install the removable face to the assembly.
For a linear diffuser, fix it to the plenum box as per the manufacturer’s instruction and recommendation. As an additional precaution, metal screws can be used to fix the linear diffuser with the plenum box.
Proper care must be taken while installing grilles and/or diffusers to avoid surrounding painted surfaces are not damaged.
Take note that dampers inside grilles or diffusers should be used only for fine adjustment during air balancing. Major adjustments should be done with a volume control damper in the duct branch. This is to avoid high sound levels.
Ductwork Insulation and Jacketing
Insulation Requirements
Indoor ducts are to be insulated with 25mm thick fiberglass insulation. Outside air ducts will be insulated with 50 mm thick insulation material as per project specifications.
Kitchen hood exhaust ducts are to be insulated with 2hr fire rating fiberglass as per project specifications.
Exposed ducts will be insulated with 50 mm thick and 48 kg/ cubic meter nominal density fiberglass board as per project specification.
Insulation Procedure
Installation of ductwork (complete with accessories) shall be checked and inspected before applying insulation at joints.
Ensure that all edge joints are closely butted, and ends are flush and seated properly.
Clean the surface of the duct to remove dust and grease.
Spread duct adhesive at the rate of 4.5 sq.m/liter.
For large ducts fix stuck-up pins at regular intervals. Apply duct adhesive on the duct (at the rate of 4.5 sq .m/liter) and fix the insulation firmly in position. Insert stoppers over the pins to hold insulation firmly to the duct. Bend the pin to lock the stopper in position and seal. The insulation in the bottom portion of the ducts should be kept under pressure by some means till it gets dry and sticks firmly to the duct.
Install the ducts as per the approved shop drawings.
Cut pieces of insulation to suit the width of joints between ducts, spread duct adhesive on duct joints, and stick insulation firmly in place. Seal the joints with aluminum foil tape.
When insulating VCDs & splitter dampers, ensure that the handle is not covered by the insulation to permit the opening and closing of dampers. Ensure access doors are not covered fully and are easy to open/close.
Where insulated ductwork passes through fire-rated walls/partitions the gap between the sleeve and ductwork shall be filled with an approved fire barrier material.
Aluminum Jacketing
Obtain necessary clearances from the engineer for insulation work (both the workmanship and quality) before proceeding with the jacketing application.
Check the materials for damage/defects before starting the fabrication works.
Take the necessary measurements for jacketing.
Develop the appropriate cutting plan for the metal sheet giving allowances for cross-sectional and longitudinal overlaps.
Cut the sheet along with the marking.
Aluminum sheet required cross bend and perform grooving.
Fabricated sheets are fixed to the insulated surface with a minimum of 50mm lapping on all on all seams and secured with pop rivets and SS screws.
Fill the joints with vapor retardant mastic or sealant.
Materials
Approved material submittal for installation method statement of HVAC:
HVAC Duct
Duct Hanger and Supports
Accessories
Fire Dampers
Motorized Damper (Fire Smoke)
Volume Damper
Zone Control Damper
Variable Air Volume (VAV) materials
Air Terminal Devices
Thermal Insulation
Fiberglass Duct Insulation
Aluminum sheet for Jacketing
Adhesive
Aluminum tape
Tools and Equipment
Hand tools
Rivet Gun
Wooden Mallet
Insulation cutting knife
Spirit level
Level threads
Step Ladder
Scaffoldings
Sheet metal cutting tools and bender
Adjustable spanners
Riveter
Drill machines
Hammers
Grinding machine
Angle cutters
Adhesive applicator
Health, Safety, and Environment
All employees shall undergo safety induction from the safety department. The task supervisor shall ensure that all men under him have undergone the induction.
All employees assigned to this task shall wear safety shoes, helmets, goggles, and hand gloves as a minimum requirement.
Necessary hazard control arising from this activity shall be briefed by the immediate supervisor to all the operatives.
The task supervisor shall inspect the area for any potential risk before commencing the activity. The area safety officer shall ensure that the risk control in the risk assessment is addressed and implemented.
Check that tools and equipment available are in compliance with the contract requirements and project specifications.
Storage, handling, and use of chemicals shall be as per the MSDS specification. Only a minimum quantity of chemicals shall be kept in the site storage area with all control measures put in place. Insulation like fiberglass cool shall be in a minimum quantity container undercover. A safe and protective storage area will be provided on the site.
Operatives will collect the adhesives and paints from the chemical stores in an appropriate metal container with a hazard label. The chemical container shall be returned to the store after use or at the end of its shift.
Daily housekeeping and waste disposal shall be done at the end of each shift.
Erection of scaffolds and inspection of scaffolds shall be carried out by third-party trained operatives.
All power tools shall be 110 V rated. Use of higher power tools other than 110 V will be subject to dispensation.
Inspection for Method Statement of HVAC Duct & Accessories Installation
Inspection request shall be raised promptly for the Consultant in accordance with the approved Inspection and Test Plan (ITP) related to the installation Method Statement of HVAC.
The inspection shall be recorded in the approved checklist attached to the approved ITP.
Records:
QC Inspection checklist report as per approved ITP for installation Method Statement of HVAC.
Inspection request duly signed off by Consultant. Moreover, verify that all mechanical and electrical inspection has been completed as per the related ITP.
As-built drawings of the HVAC duct, fittings, and accessories from the final construction.
References:
Technical Specification
Project Specifications
SMACNA (Sheet Metal and Air Conditioning Contractors’ National Association) HVAC (Heating, Ventilation, and Air Conditioning)
Duct Construction Standards
AS 1554 SAA Structural Steel Welding Code
Approved Technical Submittals
Approved Shop Drawings
Manufacturer’s Instructions
See other related MEP Installation Method Statements
Method Statement for Electrical Conduits and Boxes Installation
Method Statement UPS (Uninterrupted Power Supply) Installation