Expert guides for HVAC contractors -- sizing, materials, connections, and installation tips.
A practical guide to sizing ductwork using the friction rate method. CFM calculations, velocity limits, quick-reference sizing tables, and the common mistakes that lead to callbacks.
Read the full guideA head-to-head comparison of the three duct materials. Cost per square foot, weight, corrosion resistance, temperature limits, and which material to specify for each application.
Read the full guideTechnical reference on the four main duct connection methods. Pressure ratings, assembly speed, when each type is appropriate, and how to specify connections when ordering.
Read the full guideThe real cost comparison between stock and custom duct fittings. Hidden costs of field modifications, when custom pays for itself, and when stock is the right call.
Read the full guideWhere installation time actually goes, and how custom-fabricated ductwork eliminates the non-productive labor that consumes 20-30% of a typical duct install.
Read the full guideStep-by-step guide to measuring rectangular and round duct. Connection type adjustments, elbow and transition measurements, and the common mistakes that cause refabrication.
Read the full guideRectangular vs round duct compared across airflow, friction loss, space requirements, cost, noise, and sealing. When to use each shape and when to use both.
Read the full guideWhat gauge means, thickness tables, SMACNA minimum gauge requirements by duct size and pressure class, cost and weight tradeoffs, and when to use each gauge.
Read the full guideEnergy loss from leaky ducts, mastic vs tape vs aerosol sealing, UL 181 ratings, SMACNA seal classes, pressure testing, and code requirements.
Read the full guideFiberglass liner vs wrap vs board insulation. R-value requirements by climate zone, vapor barriers, and insulating in unconditioned vs conditioned spaces.
Read the full guidePressure classes, gauge requirements, sealing classes, SMACNA standards, fire damper requirements, access doors, and higher velocity considerations for commercial systems.
Read the full guideVelocity noise, turbulence from fittings, oil canning, breakout noise. Solutions including lined duct, turning vanes, radius elbows, and velocity limits.
Read the full guideSupply vs return plenums, sizing by system tonnage, static pressure considerations, construction details, connection patterns, and common installation mistakes.
Read the full guideTaper angle rules, pressure loss from abrupt vs gradual transitions, offset transitions, sizing rules, and the common mistakes that cause turbulence and noise.
Read the full guideAirflow dynamics, pressure drop comparison with loss coefficients, when a wye is better for lower turbulence, when a tee saves space, and branch sizing guidance.
Read the full guideFriction rate differences, cost comparison (material vs installed), code limitations on flex duct, when flex makes sense, and when sheet metal wins.
Read the full guideStatic pressure limitations, smaller duct sizing, short run requirements, common configurations, round vs rectangular considerations for ducted mini split systems.
Read the full guideMaterial cost by weight, labor hours per fitting type, markup percentages, residential vs commercial pricing, common estimating mistakes, and a worked example.
Read the full guideMaterial choices for appearance, round vs rectangular aesthetics, connection type visibility, paint and powder coat options, and ceiling clearance considerations.
Read the full guideMoisture concerns, insulation requirements, vapor barriers, support and hanging methods, pest protection, material choices, and access for maintenance.
Read the full guideResidential and commercial kitchen exhaust requirements, CFM sizing rules, duct material requirements, grease duct specifications, and makeup air codes.
Read the full guideTotal external static pressure, component loss budgets, friction charts, equivalent length tables, manometer measurement, and troubleshooting high static.
Read the full guidePressure classes, construction classes, gauge requirements by size, reinforcement methods, seal classes, hanger spacing, and when code requires SMACNA compliance.
Read the full guideTrapeze vs strap hangers, SMACNA support spacing tables, hanger rod sizing, seismic bracing, vertical riser supports, and common installation mistakes.
Read the full guideWhy returns are undersized, sizing for full system CFM, single central vs distributed returns, transfer grilles, panned return problems, and code requirements.
Read the full guideS-offsets vs single offsets, calculating dimensions, equivalent lengths, when to use an offset vs two elbows, and ordering dimensions for space-constrained installations.
Read the full guideSealing trunk ends, access doors for cleaning, code requirements, removable end caps, test hole plugs, and maintaining indoor air quality through accessible ductwork.
Read the full guideHow to select the correct elbow radius ratio, the pressure loss difference between short- and long-radius elbows, turning vane requirements, and when to use mitered vs radius construction.
Read the full guideWhen to use eccentric vs concentric reducers, the 15-degree taper rule for pressure recovery, sizing rules for gradual vs abrupt reductions, and condensate drainage considerations.
Read the full guideStandard wye angles, how to size branches for intended CFM splits, pressure loss coefficients, and installation orientation best practices for horizontal and vertical runs.
Read the full guideTDC vs TDF flange construction, corner clip installation, gasket selection, clamp torque sequence, pressure rating by flange size, and the maintenance advantages over slip-and-drive.
Read the full guideHow to calculate required return boot size, face velocity targets for quiet operation, grille free-area correction factors, and placement rules for effective return air collection.
Read the full guideHow to calculate the correct round diameter for a square-to-round transition, minimum taper length for low turbulence, offset vs centered configurations, and field measurement tips.
Read the full guideWhen a cross fitting makes sense over two tees, CFM balancing across four branches, pressure loss characteristics, and design rules for symmetric and asymmetric cross configurations.
Read the full guideWhen stainless steel is required over galvanized, alloy selection for corrosive environments, temperature limits, gauge requirements, and cost premium justification for laboratory and kitchen applications.
Read the full guideHow duct pressurization testing works, SMACNA leakage class requirements, test pressure procedures, interpreting results, and systematic leak location techniques.
Read the full guideHow ACCA Manual D calculates available static pressure, friction rate determination, critical path identification, and how to use friction charts to size every duct section correctly.
Read the full guideHow to convert Manual J loads to room CFM requirements, calculate duct areas from target velocities, and step down trunk sizes through a complete residential system.
Read the full guideHow zone damper systems work, bypass damper sizing to protect the blower, why dead-heading is dangerous, and duct sizing rules for multi-zone residential and light commercial systems.
Read the full guideIRC M1502 requirements for dryer exhaust, why HVAC duct cannot substitute for dryer vent, fire hazard mechanics, material differences, and the common mistakes that create dangerous installations.
Read the full guideType I vs Type II hood requirements, NFPA 96 duct construction standards, welded seam requirements, grease accumulation and fire risk, and access panel placement rules.
Read the full guideHow RTU ductwork differs from split-system design, curb adapter sizing, supply and return plenum construction, roof penetration flashing, and condensate management.
Read the full guideHow to identify the critical outlet, the proportional balancing method step by step, using a flow hood correctly, and when to resize vs use dampers to achieve balanced airflow.
Read the full guideHow mastic and foil tape differ in application and long-term adhesion, UL 181A vs 181B listings, when each is appropriate, and why mastic outperforms tape on joints subject to thermal cycling.
Read the full guideThe engineering differences between supply and return duct systems, pressure balancing requirements, single vs distributed returns, and the most common design mistakes that cause comfort complaints.
Read the full guideWarning signs that ductwork has failed, how to decide between repair and replacement, what drives replacement cost, and how to specify new ductwork to avoid repeating original design errors.
Read the full guideWhy fan CFM ratings are misleading at system resistance, diameter selection tables for bathroom and kitchen exhaust fans, equivalent length method, and code compliance requirements.
Read the full guideConstruction differences, air leakage performance, acoustic attenuation comparison, durability and lifespan expectations, and the specific applications where each material is the right choice.
Read the full guideHow to measure total external static pressure, interpret high and normal readings, isolate the high-resistance component, and correct static pressure problems with proper duct sizing.
Read the full guideStep-by-step installation for slip-and-drive and TDC flange connections, mastic application technique, hanger spacing requirements, and a pre-insulation inspection checklist.
Read the full guideThe true cost of field fabrication vs shop-ordered fittings, when custom fabrication wins on quality and labor, how to specify fittings correctly, and the jobs where field work still makes sense.
Read the full guideVelocity targets and maximum limits for residential, commercial, and industrial systems, how velocity drives noise and pressure loss, and how to calculate required duct area from CFM and velocity targets.
Read the full guideWhy makeup air is required, how to size replacement air quantity, delivery method selection for commercial kitchens and industrial exhaust, duct sizing, and applicable code references.
Read the full guideQuantifying the heat gain penalty from attic ducts, IECC insulation requirements by climate zone, condensation prevention, hanger systems for truss construction, and the case for conditioned attics.
Read the full guide