Apprentice Q&A Pages

337 dedicated commercial HVAC and sheet metal Q&A pages.

#1 · What's the difference between red, green, and yellow aviation snips?Hand Tools & Safety · YELLOW · Check First #2 · When should I use a folding tool (bar folder) versus hand seamers?Hand Tools & Safety · YELLOW · Check First #3 · What is the proper way to set a wedge anchor (drop-in) in concrete without blowing out the hole?Hand Tools & Safety · YELLOW · Check First #4 · How do I know what size masonry bit to use for a 3/8" rod anchor?Hand Tools & Safety · YELLOW · Check First #5 · What's the safest way to cut spiral duct with a grinder or sawzall?Hand Tools & Safety · YELLOW · Check First #6 · How do I prevent metal shavings from getting in my eyes when drilling overhead?Hand Tools & Safety · YELLOW · Check First #7 · When is it required to wear cut-resistant gloves when handling raw metal edges?Hand Tools & Safety · YELLOW · Check First #8 · How do I correctly use a duct stretcher without bending the drive?Hand Tools & Safety · YELLOW · Check First #9 · What's the right torque or feel for tightening bolts on a TDC/TDF connection?Hand Tools & Safety · RED · Stop / Verify #10 · How do I keep my tape measure from snapping and kinking on 20-foot spans?Hand Tools & Safety · YELLOW · Check First #11 · How do I tell the difference between a Pittsburgh seam and a snap-lock seam?Duct Assembly · YELLOW · Check First #12 · What's the trick to seating a stubborn Pittsburgh seam on a large rectangular fitting?Duct Assembly · YELLOW · Check First #13 · How do you properly bend and install a slip and drive (S&D) connection?Duct Assembly · RED · Stop / Verify #14 · Which way does the "drive" face on a vertical drop?Duct Assembly · YELLOW · Check First #15 · How do I install TDC/TDF corners without smashing them or bending the flange?Duct Assembly · YELLOW · Check First #16 · Do I put the butyl gasket tape on the inside or outside of the bolt holes on a TDC flange?Duct Assembly · YELLOW · Check First #17 · How far apart should the cleats be on a TDC/TDF transverse joint?Duct Assembly · YELLOW · Check First #18 · What's the easiest way to line up massive ductwork pieces on a duct jack (Genie lift)?Duct Assembly · GREEN · Learn / Reference #19 · How do I fix a piece of rectangular duct if it's knocked together out of square?Duct Assembly · YELLOW · Check First #20 · What's the proper way to cross-brake a piece of flat metal in the field?Duct Assembly · YELLOW · Check First #21 · How do I calculate how much all-thread rod to cut for a trapeze hanger?Hangers & Supports · YELLOW · Check First #22 · What's the standard spacing for hangers on commercial rectangular duct?Hangers & Supports · YELLOW · Check First #23 · How do I use a laser level to establish a perfectly straight hanger line?Hangers & Supports · YELLOW · Check First #24 · When building a unistrut trapeze, should the strut open face point up or down?Hangers & Supports · YELLOW · Check First #25 · How do I square up my hanger points off a structural I-beam?Hangers & Supports · YELLOW · Check First #26 · What's the rule of thumb for how far the all-thread should stick out below the unistrut nut?Hangers & Supports · YELLOW · Check First #27 · How do I support a massive 90-degree elbow so it doesn't sag on the heel?Hangers & Supports · YELLOW · Check First #28 · When do I need to use isolation pads on my duct hangers?Hangers & Supports · RED · Stop / Verify #29 · How do I hang spiral duct using cable hangers (Gripple) instead of strap?Hangers & Supports · YELLOW · Check First #30 · What's the proper gauge of hanger strap for medium-pressure ductwork?Hangers & Supports · YELLOW · Check First #31 · What's the difference between water-based mastic and solvent-based duct sealant?Sealing & Insulation · YELLOW · Check First #32 · Do I need to seal the longitudinal seams, or just the transverse joints?Sealing & Insulation · YELLOW · Check First #33 · How do I apply fiberglass mesh tape with mastic without it wrinkling?Sealing & Insulation · YELLOW · Check First #34 · What is the proper overlap for duct wrap (blanket insulation) on commercial jobs?Sealing & Insulation · YELLOW · Check First #35 · How do I correctly staple and tape the vapor barrier on duct wrap?Sealing & Insulation · YELLOW · Check First #36 · What's the trick to cutting duct liner so the edges don't fray?Sealing & Insulation · YELLOW · Check First #37 · How many weld pins do I need per square foot when installing internal acoustic liner?Sealing & Insulation · RED · Stop / Verify #38 · What do I do if I accidentally poke a hole in the insulation vapor barrier?Sealing & Insulation · YELLOW · Check First #39 · How do I apply water-based mastic when it's freezing cold on the jobsite?Sealing & Insulation · YELLOW · Check First #40 · What's the clean-up procedure for getting mastic off my tools (and hands)?Sealing & Insulation · YELLOW · Check First #41 · What should I be staging for the journeyman while they are measuring the next piece?Site Awareness · RED · Stop / Verify #42 · How do I organize the hardware bucket so we aren't losing bolts and nuts on a scissor lift?Site Awareness · YELLOW · Check First #43 · What's the right way to load a scissor lift so we don't exceed the weight capacity?Site Awareness · GREEN · Learn / Reference #44 · How do I communicate over the noise of the jobsite when backing up a lift?Site Awareness · YELLOW · Check First #45 · What information does the foreman need when I go do a material count?Site Awareness · RED · Stop / Verify #46 · How do I properly strap down sheet metal on a material cart so it doesn't slide off?Site Awareness · GREEN · Learn / Reference #47 · What is a "block out" in concrete, and why do we need to check them before pouring?Site Awareness · YELLOW · Check First #48 · How do I keep my cordless batteries from dying in cold weather?Site Awareness · GREEN · Learn / Reference #49 · What's the standard procedure for end-of-day jobsite cleanup for sheet metal crews?Site Awareness · YELLOW · Check First #50 · How do I ask the foreman a question without interrupting a layout calculation?Site Awareness · YELLOW · Check First #51 · How do I determine the "right" and "left" hand side of a VAV box?VAVs & Fan Coils · YELLOW · Check First #52 · What is the minimum clearance needed for the VAV control panel access?VAVs & Fan Coils · RED · Stop / Verify #53 · How do I transition from rectangular duct to the round inlet of a VAV?VAVs & Fan Coils · YELLOW · Check First #54 · Should a VAV box be hung independently of the ductwork?VAVs & Fan Coils · YELLOW · Check First #55 · How many duct diameters of straight pipe do I need before the inlet of a VAV box?VAVs & Fan Coils · YELLOW · Check First #56 · What's the best way to support a heavy fan coil unit above a drop ceiling?VAVs & Fan Coils · RED · Stop / Verify #57 · Where do the auxiliary drain pans go under a fan coil unit?VAVs & Fan Coils · YELLOW · Check First #58 · How do I install a flexible connection (canvas connector) at the equipment discharge?VAVs & Fan Coils · RED · Stop / Verify #59 · Do I need to internally line the first 10 feet of duct leaving the VAV box?VAVs & Fan Coils · YELLOW · Check First #60 · How do I properly secure the reheat coil to the VAV discharge?VAVs & Fan Coils · YELLOW · Check First #61 · What is the SMACNA maximum allowable length for a flex duct run?Flex Duct & Grilles · RED · Stop / Verify #62 · How do I properly strap flex duct to avoid "sag" and restricted airflow?Flex Duct & Grilles · YELLOW · Check First #63 · What's the correct way to seal a flex duct connection (zip tie vs. metal band vs. tape/mastic)?Flex Duct & Grilles · RED · Stop / Verify #64 · How do I cut a spin-in collar into a piece of round spiral duct?Flex Duct & Grilles · YELLOW · Check First #65 · What's the difference between a lay-in diffuser and a surface-mount grille?Flex Duct & Grilles · YELLOW · Check First #66 · How do I install a register boot in a hard-lid (drywall) ceiling so it sits flush?Flex Duct & Grilles · YELLOW · Check First #67 · How do I balance a scissor lift while cutting in a heavy linear slot diffuser?Flex Duct & Grilles · YELLOW · Check First #68 · What's the trick to running flex duct over a congested plumbing rack without pinching it?Flex Duct & Grilles · YELLOW · Check First #69 · How do I install a volume damper in a spin-in collar before attaching the flex?Flex Duct & Grilles · RED · Stop / Verify #70 · How do I keep my flex duct cuts clean without tearing the inner core?Flex Duct & Grilles · YELLOW · Check First #71 · What is the difference between a dynamic and a static fire damper?Dampers · RED · Stop / Verify #72 · How do I install a retaining angle on a fire damper in a masonry wall?Dampers · RED · Stop / Verify #73 · Does the fire damper sleeve get attached to the wall or just the retaining angles?Dampers · RED · Stop / Verify #74 · How much expansion clearance do I need to leave around a fire damper sleeve?Dampers · RED · Stop / Verify #75 · Where is the exact placement for an access door next to a fire damper?Dampers · RED · Stop / Verify #76 · Can I use regular duct sealant on the breakaway joints of a fire damper?Dampers · RED · Stop / Verify #77 · How do I install a smoke damper actuator so the electrician can reach it?Dampers · RED · Stop / Verify #78 · What's the correct way to set a manual balancing damper quadrant so it doesn't rattle?Dampers · RED · Stop / Verify #79 · Do motorized control dampers need to be installed perfectly level to work?Dampers · YELLOW · Check First #80 · How do I frame an opening for a backdraft damper in a brick shaft?Dampers · RED · Stop / Verify #81 · How do I find the duct elevations (Bottom of Duct / BOD) on the mechanical plans?Blueprint Reading · YELLOW · Check First #82 · What does a "hash mark" with a number inside a duct run mean on a blueprint?Blueprint Reading · YELLOW · Check First #83 · How do I locate the architectural grid lines to measure out my hanger locations?Blueprint Reading · YELLOW · Check First #84 · What is the symbol for a drop (duct going down) versus a rise (duct going up)?Blueprint Reading · YELLOW · Check First #85 · How do I cross-reference the mechanical plan with the reflected ceiling plan (RCP)?Blueprint Reading · YELLOW · Check First #86 · What does it mean when the print says "field verify" for a dimension?Blueprint Reading · YELLOW · Check First #87 · How do I read the equipment schedule to know which VAV goes in which room?Blueprint Reading · YELLOW · Check First #88 · What does "NIC" mean when it's stamped next to a piece of equipment?Blueprint Reading · YELLOW · Check First #89 · How do I scale a drawing if the architect forgot to put dimensions on the mechanical room?Blueprint Reading · RED · Stop / Verify #90 · How do I identify a fire-rated wall on the architectural drawings?Blueprint Reading · RED · Stop / Verify #91 · How do I build an end-cap out of flat metal in the field?Field Mods · YELLOW · Check First #92 · What's the formula for finding the throat radius of a standard 90-degree elbow?Field Mods · GREEN · Learn / Reference #93 · How do I field-cut a tap into the side of a massive low-pressure trunk line?Field Mods · YELLOW · Check First #94 · How do I fix a round pipe that's been crushed during shipping so it fits together?Field Mods · GREEN · Learn / Reference #95 · What's the best way to modify a square-to-round transition if the VAV is off-center?Field Mods · YELLOW · Check First #96 · How do I safely drill out spot welds to modify a factory fitting?Field Mods · RED · Stop / Verify #97 · How do I correctly rivet a patch plate over an accidental hole in high-pressure duct?Field Mods · YELLOW · Check First #98 · What is the proper spacing for tek screws on a 24-inch round slip joint?Field Mods · YELLOW · Check First #99 · How do I seal a duct penetration going through a non-rated CMU wall?Field Mods · YELLOW · Check First #100 · What is "oil-canning," and how do I cross-brake duct to prevent it?Field Mods · YELLOW · Check First #101 · How do I square up and level a roof curb on a pitched roof?Roof Work & Curbs · YELLOW · Check First #102 · What's the difference between a canted curb and a flat curb?Roof Work & Curbs · YELLOW · Check First #103 · How do I install a pitch pocket for refrigerant lines penetrating the roof deck?Roof Work & Curbs · YELLOW · Check First #104 · What is the proper way to set a curb adapter when replacing an old RTU?Roof Work & Curbs · RED · Stop / Verify #105 · How do I run exposed roof ductwork so it meets wind-load requirements?Roof Work & Curbs · YELLOW · Check First #106 · What's the procedure for installing a gooseneck (hood) for an outside air intake?Roof Work & Curbs · RED · Stop / Verify #107 · How do I seal the duct drop inside a roof curb so water can't get into the building?Roof Work & Curbs · YELLOW · Check First #108 · Where do I place the vibration isolators on a custom curb?Roof Work & Curbs · YELLOW · Check First #109 · How do I coordinate with the roofer before cutting the roof deck for a new curb?Roof Work & Curbs · YELLOW · Check First #110 · What is a "doghouse" on a roof, and how do I flash duct penetrating the side of it?Roof Work & Curbs · YELLOW · Check First #111 · What is the required clearance to combustibles for a Type 1 grease duct (black iron)?Specialty Duct · RED · Stop / Verify #112 · How do I layout a welded grease duct slope so grease drains toward the hood?Specialty Duct · RED · Stop / Verify #113 · What is the proper welding procedure (MIG vs. TIG) for 16-gauge stainless steel duct?Specialty Duct · RED · Stop / Verify #114 · How do I test a welded grease duct system for leaks (light test vs. water test)?Specialty Duct · RED · Stop / Verify #115 · What's the trick to installing fire-wrap (Zero Clearance insulation) on grease duct?Specialty Duct · RED · Stop / Verify #116 · How do I handle and install exposed double-wall spiral duct without scratching it?Specialty Duct · RED · Stop / Verify #117 · What are the specific hangers required for PVC-coated duct in a chemical exhaust system?Specialty Duct · RED · Stop / Verify #118 · How do I install a cleanout access door in a welded grease duct?Specialty Duct · RED · Stop / Verify #119 · Why does aluminum ductwork require closer hanger spacing than galvanized?Specialty Duct · RED · Stop / Verify #120 · How do I transition from rectangular black iron to a high-velocity exhaust fan?Specialty Duct · RED · Stop / Verify #121 · How do I read the seismic engineering details for cable bracing on heavy duct?Sealing & Insulation · RED · Stop / Verify #122 · What's the proper way to swage a Gripple or cable lock for a seismic sway brace?Sealing & Insulation · RED · Stop / Verify #123 · At what duct size or weight does the code require lateral and longitudinal seismic bracing?Sealing & Insulation · RED · Stop / Verify #124 · How do I install rigid bracing (strut) without creating a sound vibration transfer?Sealing & Insulation · RED · Stop / Verify #125 · What is the safest way to drop ductwork down a 4-story mechanical shaft?Sealing & Insulation · RED · Stop / Verify #126 · How do we support vertical riser ductwork at each floor penetration?Sealing & Insulation · RED · Stop / Verify #127 · What is a "Z-bracket" and how do I use it to secure shaft duct to the concrete deck?Sealing & Insulation · RED · Stop / Verify #128 · How do I ensure fire-stopping is done correctly around duct penetrating a floor slab?Sealing & Insulation · RED · Stop / Verify #129 · How do I safely rig ductwork while standing on a leading edge (harnessed in)?Sealing & Insulation · RED · Stop / Verify #130 · What do I do if the structural beams shown on the print don't exist in the field?Sealing & Insulation · RED · Stop / Verify #131 · How do I measure an offset when the duct has to drop 14 inches and move over 22 inches?Field Math & Measuring · YELLOW · Check First #132 · What is the Pythagorean theorem (AField Math & Measuring · YELLOW · Check First #133 · How do I take field measurements for an OG (Ogee) offset?Field Math & Measuring · RED · Stop / Verify #134 · What is "take-back" or "allowance" when measuring for a slip/drive vs. TDC fitting?Field Math & Measuring · YELLOW · Check First #135 · How do I accurately measure the diagonal of a room to make sure my main trunk is parallel?Field Math & Measuring · YELLOW · Check First #136 · How do I lay out a round lateral (wye) branch using a template?Field Math & Measuring · YELLOW · Check First #137 · What's the formula to find the circumference of a spiral pipe when cutting a saddle tap?Field Math & Measuring · YELLOW · Check First #138 · How do I measure a canvas connector so the equipment has room to vibrate without pulling?Field Math & Measuring · RED · Stop / Verify #139 · How do I draft a field sketch so the fab shop makes exactly what I need?Field Math & Measuring · RED · Stop / Verify #140 · How do I handle duct that arrives from the shop fabricated backwards?Field Math & Measuring · YELLOW · Check First #141 · Who has the right-of-way in a ceiling plenum: Ductwork, Gravity Plumbing, or Sprinklers?Trade Coordination · YELLOW · Check First #142 · How do I negotiate a clash with the electrician's cable tray?Trade Coordination · YELLOW · Check First #143 · What is the process for submitting an RFI (Request for Information) when a clash stops work?Trade Coordination · YELLOW · Check First #144 · How do I install ductwork around a structural column without ruining the airflow?Trade Coordination · YELLOW · Check First #145 · What do I do if the architectural ceiling is dropped lower than the plans state?Trade Coordination · YELLOW · Check First #146 · How do I route ductwork so I don't block access to VAV control panels?Trade Coordination · YELLOW · Check First #147 · How do I mark out my floor penetrations before the concrete floor is poured?Trade Coordination · YELLOW · Check First #148 · How do I protect my installed ductwork from getting damaged by other trades on lifts?Trade Coordination · YELLOW · Check First #149 · What happens if I accidentally cut a post-tension cable in a concrete slab?Trade Coordination · RED · Stop / Verify #150 · How do we coordinate setting equipment on a roof with the crane operator?Trade Coordination · RED · Stop / Verify #151 · What are the standard hand signals for communicating with a crane operator?Rigging & Equipment · RED · Stop / Verify #152 · How do I calculate the center of gravity for an asymmetrical Make-Up Air Unit (MAU)?Rigging & Equipment · RED · Stop / Verify #153 · What's the difference between a choker hitch and a basket hitch when slinging an RTU?Rigging & Equipment · RED · Stop / Verify #154 · How do I determine the load capacity of my synthetic rigging straps based on the angle?Rigging & Equipment · RED · Stop / Verify #155 · What is the procedure for safely offloading semi-trucks on a busy city street?Rigging & Equipment · RED · Stop / Verify #156 · How do I set a split-system air handler in a tight mechanical room using machine skates?Rigging & Equipment · RED · Stop / Verify #157 · What is a spreader bar, and when must I use one to lift an RTU?Rigging & Equipment · RED · Stop / Verify #158 · How do I verify the RTU curb gasket is seated perfectly before the crane unhooks?Rigging & Equipment · RED · Stop / Verify #159 · What's the protocol for crane lifts if the wind speed exceeds 20 mph?Rigging & Equipment · RED · Stop / Verify #160 · How do I safely rig and hoist ductwork up the outside of a building using a material hoist?Rigging & Equipment · RED · Stop / Verify #161 · Where in the SMACNA manual do I find the gauge requirements for +4" WG static pressure duct?Code & Compliance · RED · Stop / Verify #162 · What is the maximum allowable leakage rate for Class A duct sealing?Code & Compliance · RED · Stop / Verify #163 · How do I identify a 2-hour vs. a 1-hour fire wall on an architectural life-safety plan?Code & Compliance · RED · Stop / Verify #164 · What is the mechanical code rule regarding the minimum outside air intake distance from a plumbing vent?Code & Compliance · RED · Stop / Verify #165 · How do I calculate the free area of a louver to ensure I meet the engineer's specs?Code & Compliance · RED · Stop / Verify #166 · What does the NFPA 90A code say about using combustible materials in a return air plenum?Code & Compliance · RED · Stop / Verify #167 · How do I prepare the ductwork for a city inspector's rough-in inspection?Code & Compliance · RED · Stop / Verify #168 · What documentation does the Fire Marshal need when inspecting smoke dampers?Code & Compliance · RED · Stop / Verify #169 · Under what conditions am I allowed to use flex duct in a commercial kitchen?Code & Compliance · RED · Stop / Verify #170 · How do I verify that our shop-fabricated fire damper sleeves meet UL listing requirements?Code & Compliance · RED · Stop / Verify #171 · Where exactly should I drill the test holes for the balancer in the main trunk line?TAB / Startup Prep · YELLOW · Check First #172 · Why do I need 5 to 10 duct diameters of straight duct downstream of the air handler?TAB / Startup Prep · YELLOW · Check First #173 · What should I check mechanically before the start-up tech powers on the RTU?TAB / Startup Prep · RED · Stop / Verify #174 · How do I perform a duct pressure test (leak test) with an orifice tube?TAB / Startup Prep · RED · Stop / Verify #175 · What do I do if a zone is starved for air and the balancer says my fitting is causing turbulence?TAB / Startup Prep · YELLOW · Check First #176 · How do I ensure all VAV damper blades are in the open position before system blow-down?TAB / Startup Prep · RED · Stop / Verify #177 · What is the procedure for blowing out the ductwork to remove dust before final grilles go on?TAB / Startup Prep · YELLOW · Check First #178 · How do I troubleshoot a fire damper that won't drop during a drop test?TAB / Startup Prep · RED · Stop / Verify #179 · Why do we need to install turning vanes in square-throat elbows, and how do they affect static pressure?TAB / Startup Prep · YELLOW · Check First #180 · How do I walk the job to punch-list my own work before the GC does?TAB / Startup Prep · YELLOW · Check First #181 · How do I perform a complete material take-off from a set of mechanical drawings?Crew Leadership · YELLOW · Check First #182 · What is the most efficient way to stage 5,000 lbs of ductwork on a floor without bottlenecking other trades?Crew Leadership · RED · Stop / Verify #183 · How do I break down a complex mechanical room layout into daily tasks for a two-man crew?Crew Leadership · RED · Stop / Verify #184 · How do I handle an apprentice who is repeatedly making the same measurement mistakes?Crew Leadership · RED · Stop / Verify #185 · What's the best way to track "Change Order" work so the company gets paid for extras?Crew Leadership · YELLOW · Check First #186 · How do I verify the fab shop's shipping manifest so I know exactly what's missing before we start?Crew Leadership · YELLOW · Check First #187 · What is the "critical path" on a construction schedule, and how does it affect our HVAC crew?Crew Leadership · RED · Stop / Verify #188 · How do I run a weekly toolbox safety talk that guys actually listen to?Crew Leadership · RED · Stop / Verify #189 · How do I build a relationship with the General Contractor's superintendent to get favors when we need them?Crew Leadership · YELLOW · Check First #190 · What's the smartest way to transition a crew from the rough-in phase to the trim/finish phase?Crew Leadership · YELLOW · Check First #191 · The roof structure sagged, and my duct is now hitting the ceiling grid. How do I re-engineer the run on the fly?Advanced Problem Solving · RED · Stop / Verify #192 · The RTU ordered was a down-discharge, but the curb was framed for side-discharge. How do I build a transition inside the curb?Advanced Problem Solving · RED · Stop / Verify #193 · The engineer specified a VAV that is physically larger than the ceiling space provided. What are my redesign options?Advanced Problem Solving · YELLOW · Check First #194 · We are short on 24x24 duct, but we have a plasma cutter and flat stock. How do I fabricate it entirely in the field?Advanced Problem Solving · RED · Stop / Verify #195 · The concrete guys poured a shaft out of plumb, and my duct won't drop straight. How do I adjust?Advanced Problem Solving · RED · Stop / Verify #196 · The electrical engineer moved the lights, and now every single diffuser has to shift 3 feet. How do I manage the rework efficiently?Advanced Problem Solving · RED · Stop / Verify #197 · We lost power to the building, but we have 40 pieces of duct to hang. How do we shoot hanger points without laser levels?Advanced Problem Solving · YELLOW · Check First #198 · The fire inspector failed our damper installation because the wall was framed too wide. How do I fix it without tearing out the wall?Advanced Problem Solving · RED · Stop / Verify #199 · A crane lift is scheduled for tomorrow, but a storm is rolling in. What is the contingency plan to secure the site?Advanced Problem Solving · RED · Stop / Verify #200 · I just realized I misread the print, and the last 100 feet of duct is 4 inches too small. Do I hide it or tell the boss immediately?Advanced Problem Solving · RED · Stop / Verify #201 · How should I handle a radius elbow that will not clear a beam?Trade Coordination · YELLOW · Check First #202 · How do I fix a branch duct tap that was laid out off center?Measuring & Layout · YELLOW · Check First #203 · What should I check when flex duct is sagging and starving a room?Flex Duct · GREEN · Standard Correction #204 · Who has right-of-way when a pipe is already in the duct path?Trade Coordination · RED · Stop / Verify #205 · What should I do if another trade is about to bury a fire damper?Fire/Smoke Dampers · RED · Stop / Verify #206 · How do I handle duct connections when the ceiling space is too tight?Trade Coordination · YELLOW · Check First #207 · Why can’t commercial kitchen grease duct just be hung level?Grease Duct · RED · Stop / Verify #208 · How do I verify fire/smoke damper orientation before cover?Fire/Smoke Dampers · RED · Stop / Verify #209 · What should I check before grease duct fire wrap gets covered?Grease Duct · RED · Stop / Verify #210 · What does it mean when a duct seam pops during pressure testing?Pressure Testing · YELLOW · Check First #211 · Why is a hard elbow right at a VAV inlet a problem?Equipment Connections · YELLOW · Check First #212 · How do I fix a whistling TDC/Ductmate flange on a large duct?Duct Assembly · GREEN · Standard Correction #213 · How do I close a blind S-cleat joint in a tight chase when I can’t reach the back?Duct Assembly · YELLOW · Check First #214 · Why is a short expanding transition noisy or choking airflow?Airflow / TAB · YELLOW · Check First #215 · How do I fix a Pittsburgh seam that was not knocked down and is leaking?Duct Assembly · GREEN · Standard Correction #216 · What do I do when an oversized first tap is starving the rest of the trunk?Airflow / TAB · YELLOW · Check First #217 · Can a structural column pass through a low-pressure return duct?Coordination · RED · Stop / Verify #218 · What do I do when sprinkler pipe is sitting on my TDC flange?Coordination · RED · Stop / Verify #219 · What do I do when drywall crushes flex duct in a wall cavity?Flex Duct · YELLOW · Check First #220 · What do I do if another trade ties cable to my duct hangers?Hangers / Supports · YELLOW · Check First #221 · What if structural bracing blocks a VAV access panel?Equipment Connections · RED · Stop / Verify #222 · What do I do when seismic bracing crosses my round duct route?Seismic / Coordination · YELLOW · Check First #223 · What if an FSD sleeve gap is packed with regular fiberglass?Fire/Smoke Dampers · RED · Stop / Verify #224 · Does a grease duct elbow need a cleanout access door?Grease Duct · RED · Stop / Verify #225 · Why is a welded grease duct bowing when it heats up?Grease Duct · RED · Stop / Verify #226 · Can galvanized duct be used on lab fume hood exhaust?Specialty Exhaust · RED · Stop / Verify #227 · Should fire damper retaining angles be screwed to the wall framing?Fire/Smoke Dampers · RED · Stop / Verify #228 · What do I do if an RTU curb gasket is torn or missing at a corner?Roof Equipment · RED · Stop / Verify #229 · Why is rooftop duct holding water on top?Rooftop Duct · YELLOW · Check First #230 · How do I fix a spiral slip joint that popped during pressure test?Pressure Testing · YELLOW · Check First #231 · How do I fix a screaming TDC/Ductmate gasket leak?Duct Assembly · GREEN · Standard Correction #232 · Why does a shallow condensate trap make an AHU drain pan overflow?Equipment Connections · YELLOW · Check First #233 · What do I do when a splitter damper blade breaks loose inside duct?Airflow / TAB · YELLOW · Check First #234 · What if an FSD actuator hums but the blades do not move?Fire/Smoke Dampers · RED · Stop / Verify #235 · How do I seal air balance test holes that blow out caps?TAB / Pressure Testing · GREEN · Standard Correction #236 · What do I do when canvas connector tears on startup?Equipment Connections · YELLOW · Check First #237 · What do I check when a branch reads zero CFM but dampers are open?Airflow / TAB · YELLOW · Check First #238 · What should I do if a hammer drill hits steel while drilling anchors in a concrete slab?Hangers / Anchoring · RED · Stop / Verify #239 · Why is my duct trapeze bowing and how should it be corrected?Hangers / Supports · YELLOW · Check First #240 · How do I stop a fan or terminal unit from swaying on long hanger rods?Seismic / Vibration · YELLOW · Check First #241 · What if heavy rectangular duct is sagging between hanger points?Hangers / Supports · RED · Stop / Verify #242 · How do I fix a vertical duct riser that is drifting out of plumb?Measuring / Layout · YELLOW · Check First #243 · Why is water getting under a rooftop curb counter-flashing?Roof / Equipment · RED · Stop / Verify #244 · Can a vertical duct riser be supported from light-gauge studs or straps?Risers / Supports · RED · Stop / Verify #245 · Why does a rooftop unit need a level curb on a sloped roof?Roof / Equipment · YELLOW · Check First #246 · Why would a large return duct implode or oil-can during commissioning?Pressure / Leakage · YELLOW · Check First #247 · Can a torn Vanstone flare be sealed with mastic?Round / Spiral · YELLOW · Check First #248 · Why would spiral duct bulge or unzip at the lockseam under pressure?Round / Spiral · YELLOW · Check First #249 · How do I fix a stripped TDC or Ductmate corner bolt?TDC / Ductmate · GREEN · Standard Correction #250 · Why is it bad to neck down a VAV discharge immediately after the box?Equipment Connections · YELLOW · Check First #251 · Why does a fan coil need a flexible connector at the duct connection?Equipment Connections · GREEN · Standard Correction #252 · How do you avoid cracking a VAV reheat coil connection when tightening piping?Equipment Connections · RED · Stop / Verify #253 · How do I fix flex duct that kinks right off the plenum box?Flex Duct · GREEN · Standard Correction #254 · How can you tell if an exterior intake louver is installed the wrong way?Louvers / Exterior Intake · RED · Stop / Verify #255 · Can multi-section fire/smoke dampers be joined with regular drywall screws?Fire/Smoke Dampers · RED · Stop / Verify #256 · Where should a fire damper sleeve sit in a rated wall opening?Fire/Smoke Dampers · YELLOW · Check First #257 · Why is duct mastic peeling off oily or wet metal?Sealing / Leakage · GREEN · Standard Correction #258 · Should round duct through a block wall have a sleeve?Penetrations / Sleeves · YELLOW · Check First #259 · Why is a cold supply tap sweating above the ceiling?Insulation / Condensation · YELLOW · Check First #260 · Why does a damper actuator run but the blades stay frozen?Controls / Dampers · YELLOW · Check First #261 · How should inactive sections of a louver be blanked off?Louvers / Exterior Air · YELLOW · Check First #262 · How do you line up multi-section linear slot diffusers so the joints look clean?QA/QC / Finish · GREEN · Standard Correction #263 · Why would a large return plenum wall oil-can or buckle inward when the air handler starts?AHU / Plenums · YELLOW · Check First #264 · Why can a flat bullnose tee cause air noise and bad balancing readings?Airflow / Fittings · YELLOW · Check First #265 · How do you line up twisted companion flanges without damaging the duct?TDC / Ductmate · GREEN · Standard Correction #266 · Why can an adjustable round elbow split open on a high-velocity duct run?Round Duct · YELLOW · Check First #267 · Can you install a duct sound attenuator if the internal media got wet?Material Handling · RED · Stop and Get Direction #268 · Do duct silencers and sound attenuators have airflow direction?Sound Attenuators · YELLOW · Check First #269 · Why can solid metal bracing around a sound attenuator make noise worse?Sound Attenuators / Fans · GREEN · Standard Correction #270 · Why is it a problem if a fire damper sleeve is squeezed by a tight wall opening?Rated Wall Penetrations · YELLOW · Check First #271 · Can you fire-caulk raw duct directly through a rated drywall wall without a sleeve?Rated Wall Penetrations · RED · Stop and Get Direction #272 · Why does smoke exhaust equipment need manufacturer clearance to combustibles?Smoke Exhaust / Jet Fans · RED · Stop and Get Direction #273 · Why does a VAV box act wrong when the flow sensor tubing is kinked?VAV / Controls · YELLOW · Check First #274 · Why do sharp offsets right at a VAV inlet cause bad CFM readings?VAV / TAB · YELLOW · Check First #275 · Why would hot air whistle out of the reheat coil frame on a VAV box?VAV / Reheat · GREEN · Standard Correction #276 · Why would a VAV show zero airflow even though the actuator is running?VAV / Controls · YELLOW · Check First #277 · What happens if an outside-air intake louver is covered from behind?Coordination / Louvers · RED · Stop and Get Direction #278 · Why does an uninsulated louver blank-off panel sweat in cold weather?Louvers / Insulation · YELLOW · Check First #279 · Why would rain leak through the center joint of a multi-section louver?Louvers / Weather · YELLOW · Check First #280 · Can a fire/smoke damper actuator burn out if line voltage is wired to the wrong motor?FSD / Controls · YELLOW · Check First #281 · Why is it bad to hang a main duct in front of an AHU coil access door?Mechanical Room Coordination · RED · Stop and Get Direction #282 · Why would a flexible fan connector balloon out and rip loose?Fan Connections · YELLOW · Check First #283 · Why can a wide TDC or TDF joint leak in the center even when the corners are bolted?TDC / TDF · GREEN · Standard Correction #284 · Why does a fan coil drain pan overflow if the P-trap is dry or unvented?FCU / Condensate · YELLOW · Check First #285 · Why do loose duct liner pin heads fail inspection?Duct Liner · GREEN · Standard Correction #286 · Why does a volume damper leak when it is bolted metal-to-metal into a sleeve?Dampers / Sealing · GREEN · Standard Correction #287 · How do you fix a linear slot plenum box that will not fit because the ceiling framing is tight?Linear Diffusers / Finish · YELLOW · Check First #288 · Can you drill hanger anchors in a post-tension no-drill zone?Anchors / Post-Tension Slabs · RED · Stop and get direction #289 · Why did the drop-in anchor blow out in a fluted pan deck?Anchors / Deck Attachments · YELLOW · Check First #290 · Why is an un-set drop-in anchor dangerous for duct hangers?Anchors / Drop-In Anchors · RED · Stop and get direction #291 · How do you anchor hanger rods on a sloped or tapered concrete beam face?Anchors / Sloped Beam Face · YELLOW · Check First #292 · Can you modify a beam clamp to fit a thick structural flange?Beam Clamps / Steel · GREEN · Standard Correction #293 · Can you hang heavy duct from the bottom chord of an open-web steel joist?Joists / Structural Coordination · RED · Stop and get direction #294 · Why are beam clamps walking down the steel after the fan starts?Beam Clamps / Vibration · YELLOW · Check First #295 · Can you hang duct from a diagonal web rod in an open-web steel joist?Joists / Structural Coordination · RED · Stop and get direction #296 · Why is a multi-tier duct trapeze twisting out of square?Trapeze / Multi-Tier Supports · YELLOW · Check First #297 · Can hold-down clamps on a trapeze cause duct leaks?Trapeze / Hold-Downs · GREEN · Standard Correction #298 · How much threaded rod needs to engage inside a coupling nut?Rods / Couplings · RED · Stop and get direction #299 · Why is the Unistrut cradle sagging under a wide duct run?Trapeze / Span Deflection · YELLOW · Check First #300 · Should seismic restraint cables have slack in them?Seismic / Cable Restraints · YELLOW · Check First #301 · Can a seismic strut touch a medical gas or copper pipe?Seismic / Trade Conflicts · RED · Stop and get direction #302 · Why is it bad to brace across a flexible duct connector?Seismic / Flex Isolation · GREEN · Standard Correction #303 · Does duct seismic bracing need lateral and longitudinal restraint?Seismic / Brace Layout · YELLOW · Check First #304 · Why are thin hanger straps slicing into round duct?Strap Hangers / Round Duct · YELLOW · Check First #305 · Can a round pipe hanger be too tight?Round Duct Supports / Split Rings · YELLOW · Check First #306 · Is one sheet metal screw enough to hold a duct hanger strap?Strap Hangers / Fasteners · RED · Stop and get direction #307 · Why does spiral duct drift side-to-side in teardrop hangers?Round Duct Supports / Lateral Drift · YELLOW · Check First #308 · Can black steel all-thread be used outdoors for rooftop supports?Exterior Hardware / Corrosion · RED · Stop and get direction #309 · Why is galvanized steel touching copper a problem?Material Compatibility / Galvanic Corrosion · RED · Stop and get direction #310 · Can a duct hanger rod block a fire sprinkler spray pattern?Coordination / Fire Sprinklers · RED · Stop and get direction #311 · Is it okay if a hanger rod barely threads into the trapeze nut?Rods / Nuts / Thread Engagement · RED · Stop and get direction #312 · Can HVAC duct be supported from acoustic ceiling grid wires?Hanger Basics / Ceiling Grid · RED · Stop and get direction #313 · Why did the screws strip out on a spiral duct coupler?Round Spiral / Couplers · GREEN · Standard Correction #314 · Why did the inner liner buckle when installing double-wall spiral duct?Double-Wall Spiral · YELLOW · Check First #315 · Why is flat-oval spiral duct bowing or pancaking under static pressure?Flat-Oval Spiral / Reinforcement · YELLOW · Check First #316 · Why did the gasket get shaved off a spiral slip joint?Factory-Gasketed Spiral · YELLOW · Check First #317 · Why does a crooked field cut make spiral duct run out of line?Spiral Cutting / Layout · GREEN · Standard Correction #318 · Can you save spiral pipe after the lockseam unzips?Spiral Cutting / Lockseam · YELLOW · Check First #319 · Why does a round saddle tap whistle after install?Saddle Taps / Airflow · GREEN · Standard Correction #320 · Why can a concentric reducer cause water pooling in round duct?Moisture Exhaust / Reducers · YELLOW · Check First #321 · Why are loop hangers buckling round spiral duct?Round Supports / Dynamic Loads · YELLOW · Check First #322 · Why is flat-oval duct deforming on a flat Unistrut support?Flat-Oval Supports · YELLOW · Check First #323 · Can a vertical spiral riser be supported by wall straps on studs?Vertical Spiral Risers · RED · Stop and get direction #324 · Why is air leaking from the spiral lockseam during a pressure test?Spiral Pressure Testing · YELLOW · Check First #325 · Is galvanized spiral duct okay for natatorium or chlorine pool air?Material Compatibility / Corrosion · RED · Stop and get direction #326 · Can standard spiral duct be used for commercial kitchen grease exhaust?Kitchen Exhaust / Grease · RED · Stop and get direction #327 · Why is round spiral duct amplifying low-frequency fan noise?Acoustic / Spiral Resonance · GREEN · Standard Correction #328 · Why is the blast gate slide jammed after installation?Industrial Exhaust / Blast Gates · YELLOW · Check First #329 · Why did the round volume damper blade get stuck in spiral duct?Round Dampers / Control · YELLOW · Check First #330 · Why did a spiral duct reducer separate during startup?Round Reducers / Mechanical Fastening · YELLOW · Check First #331 · Why did the slot diffuser boot rotate after connecting the round branch?Diffuser Finish / Slot Plenums · GREEN · Standard Correction #332 · Can over-tightening round companion rings cause leaks?Companion Rings / Gaskets · GREEN · Standard Correction #333 · Why did the flat-oval longitudinal seam open on warm air discharge?Flat-Oval / Thermal Expansion · YELLOW · Check First #334 · Why is there a gap under the heel of a round saddle tap?Saddle Taps / Fit-Up · GREEN · Standard Correction #335 · Why is shower or locker exhaust leaking water through spiral duct seams?Condensation / Exhaust · YELLOW · Check First #336 · Why is a big gap around round duct through a floor slab a fire/smoke issue?Fire Barrier / Floor Penetrations · RED · Stop and get direction #337 · How much collar engagement does a spiral fitting need?Spiral Fittings / Collar Engagement · YELLOW · Check First