Creating Cleaning Access Openings in Ductwork
By: Wayne Tracy
There will be times on jobs where you will have to cut sheet metal ducting to get access for cleaning. You should check with state, county, and local authorities to see if any special licensing or permits are required in your area before you do this. It does vary widely from state to state.
There are several tools available for cutting openings in sheet metal. You can use simple hand held tin snips, a drill powered sheer, drill powered circle cutters, electric sheers or pneumatic cutters. All will create the openings you need; obviously the power tools are quicker and neater than hand held tools.
The reasons you may have to cut holes in sheet metal are as follows.
- To gain access to the evaporator coil in the air handler.
- To clean supply and return plenum boxes.
- To gain access to long trunk lines.
- To clean large over-sized ducting you cannot get under negative pressure.
- To clean around obstacles in duct runs such as turning vanes, dampers, VAV boxes, etc.
- Create man-size openings to crawl into large ducting for cleaning.
The size of hole you cut should be in direct proportion to the work you need to do. Some guidelines would be as follows:
- A 1″ hole is sufficient to insert an air whip and duct ball on long runs of ducting.
- A 4″ to 5″ hole is usually sufficient to insert a cobra cable and brush on long runs of ducting.
- A 10″ hole is sufficient to reach in with a vacuum hose and attachment to hand vacuum a plenum box, trunk line, or clean an evaporator coil.
- A 10″ hole is sufficient when connecting the pogo pole and/or adapter plate to a plenum box or trunk line.
The size of hole needed for a body to enter ducting will depend on the size of the person entering. For the average person a 16″ hole is usually sufficient. Note: Before sending someone inside ducting make sure it is adequately supported to carry the weight of the person and that all OSHA Confined Space and other safety standards are followed if applicable to the job you are doing.
Since you will be altering someone’s property you should let the homeowner, building owner/manager know that you will be cutting into their ductwork and explain the procedure for doing this, why you need to make the access cuts, and how you will seal it afterwards.
After cutting access holes and cleaning the accessed areas you will need to seal these cuts so they are airtight. The patch should always be 1″ larger then the hole you cut and sealed with screws, foil tape and in some case an approved duct sealant. ½” self tapping, hex head screws should be applied every 4″ around the plate then the plate edges should be covered with approved foil tape on all four sides. In some cases, especially on commercial jobs and pressurized lines you may be required to use duct sealant as well.
As a rule if you carry a supply of 6″ & 12″ sheet metal patches of 26 gauge galvanized metal in your truck you should be prepared for most jobs. When doing larger commercial jobs you’ll also want to have some 18″ patches on hand.
Never make cuts in flexible/insulated ductwork. If you need to get access into flex lines you have to cut it and then use sheet metal couplings to rejoin the cut section.
When cutting into insulated ducting, be sure you repair or patch the insulation you cut back to a sealed and leak proof condition.
Listed below are a few basic guidelines to sealing ductwork:
- Duct Tape is not an approved material for sealing ductwork – you must use a UL approved foil tape.
- Metal patches must overlap the opening by 1″ on all sides
- Screws should be used every 4″ on center.
- Metal patches must be sealed with caulking, mastic, duct sealant, gaskets, and/or approved foil tape.
- Approved removable duct access doors may also be used instead of metal patches.
This article is meant to be a guideline only. For exact requirements please check with your state and local officials for requirements in your area. You can also refer to NADCA (National Air Duct Cleaners Association) Standard 05 for more information on Service Opening Requirements.