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Airside & Ductwork
Duct Sizer
Size round and rectangular ducts by equal friction or velocity method. Darcy-Weisbach with Colebrook friction factor.
Airside
Duct Static Pressure
Build a critical air path with duct segments and equipment losses to calculate total external static pressure for fan selection.
Airside
Duct Area / Size Calculator
Size round or rectangular ducts from CFM and velocity. Equivalent diameter conversion, rectangular alternatives table, SMACNA pass/fail.
Airside
Static Pressure Budget
Build up total ESP for fan selection — coils, filters, OA louvers, dampers, duct system. Live budget bar with typical system ranges.
Airside
Fan Power Calculator
Calculate brake horsepower, select NEMA motor size, and estimate full load amps and annual energy from CFM and total static pressure.
Airside
Fan Energy Cost Calculator
BHP, NEMA motor selection, annual energy cost, and VFD savings from CFM, static pressure, and fan efficiency.
Airside
Velocity Calculator
Duct and pipe velocity with pass/fail against ASHRAE/SMACNA limits. Round, rectangular ducts and 6 pipe application types.
Airside
Filter Pressure Drop
MERV 8–16 filter ΔP at any face velocity. Clean and dirty pressure drop, design ΔP average, and total bank area for multiple filters.
Airside
Diffuser Count Estimator
Estimate diffuser quantity from total CFM, room area, and CFM per diffuser. Standard size capacity table and approximate spacing grid.
Airside
Grille & Register Sizing
Size supply, return, and exhaust grilles from CFM and face velocity. Get recommended grille dimensions.
Airside
VAV Box Sizing
Size VAV terminal units from cooling and heating loads. Calculate max CFM, min CFM, and recommended box diameter.
Airside
Fan Affinity Law Calculator
Calculate new CFM, static pressure, and BHP when fan speed changes using fan affinity laws.
Airside
Duct Leakage Calculator
Calculate duct leakage CFM by SMACNA class, check against ASHRAE 90.1 limits, and estimate energy penalty.
Airside
Hydronics & Piping
Hydronic Pipe Sizer
Size hydronic piping for water and glycol systems by equal friction or velocity. Covers steel, copper, CPVC, and PEX.
Hydronics
Pipe Head Loss
Calculate total pump head for a hydronic circuit. Add pipe segments and equipment losses to get system head in ft and psi.
Hydronics
Pump Selector
Size hydronic pumps from GPM and total dynamic head. Outputs water horsepower, brake horsepower, NEMA motor size, FLA, and annual energy.
Hydronics
Pump Head Estimator
Build TDH from pipe friction, coils, control valves, chiller, strainers, and elevation. Live breakdown with BHP estimate.
Hydronics
Pipe Velocity + Friction Check
Instant Darcy-Weisbach velocity and friction loss for any pipe size. Pass/fail badges against ASHRAE velocity limits.
Hydronics
Glycol Correction Factor
Correct GPM and pump head for ethylene or propylene glycol. Freeze point, specific gravity, viscosity, and heat capacity by concentration.
Hydronics
Expansion Tank Sizing
ASME method sizing for closed hydronic systems. Covers water and glycol with acceptance volume, pre-charge pressure, and expansion factor.
Hydronics
GPM / Tons / ΔT Calculator
Solve for any one of GPM, tons, or ΔT in the hydronic heat transfer equation. Glycol correction factors included.
Hydronics
Balancing Valve Cv Calculator
Calculate required Cv for balancing valves in hydronic systems. Includes fluid correction for glycol, valve authority, and standard valve sizing table.
Hydronics
Control Valve Cv & Authority
Calculate control valve Cv, valve authority, rangeability, and equal-percentage flow characteristic for hydronic HVAC systems.
Hydronics
Cooling Tower Calculator
Calculate cooling tower tons, approach, water make-up, and Legionella risk from operating conditions.
Hydronics
Pipe Insulation Heat Loss
Calculate bare and insulated pipe heat loss using cylindrical geometry. Includes condensation risk analysis.
Hydronics
Loads & Ventilation
Quick Load Estimator
Rule-of-thumb cooling tons, supply CFM, and heating MBH from square footage by building type and climate zone.
Loads
Heating BTU Calculator
Three methods: airside (1.08×CFM×ΔT), space rule-of-thumb, and boiler/furnace sizing with fuel consumption output.
Loads
Sensible vs Latent Split
SHR from BTU/hr inputs or airflow conditions. Visual sensible/latent bar and equipment dehumidification guidance by space type.
Loads
Supply Air Temp Calculator
Solve for SAT, room temp, CFM, or sensible load using Q = 1.08 × CFM × ΔT with altitude correction.
Loads
Ventilation Calculator
ASHRAE 62.1-2019 §6.2.2 per-zone OA rates. Vbz = Rp×P + Ra×A, Voz = Vbz/Ez. 14 space types with auto-loaded rates.
Ventilation
ACH Calculator
Solve for air changes per hour, CFM, or room volume. Space type reference with IMC/ASHRAE 62.1/170 requirements.
Ventilation
OA / RA % Calculator
Calculate outdoor air and return air percentages from CFM values or a target OA%. Visual bar gauge and economizer analysis.
Ventilation
Mixed Air Temp Calculator
MAT from OA and return air streams. Flow diagram, enthalpy, humidity ratio mixing, and economizer opportunity alert.
Airside
Infiltration Load Calculator
Calculate heating and cooling infiltration loads from building envelope leakage using ACH method with altitude correction and humidity ratio inputs.
Loads
Lighting Heat Gain Calculator
Calculate sensible cooling load from lighting including radiant/convective split, CLF adjustment, and ASHRAE 90.1-2019 LPD compliance check.
Loads
Wall Assembly U-Value
Calculate overall R-value and U-value for multi-layer wall assemblies with framing correction per ASHRAE 90.1.
Loads
Window Solar Heat Gain
Calculate window solar heat gain and conduction gain by orientation, SHGC, latitude, and shading factors using ASHRAE peak SHGF values.
Loads
DOAS Sizing Calculator
Size a dedicated outdoor air system from occupancy, space type, and design conditions. Outputs total OA CFM, coil capacity, and ERV pre-conditioning load.
Ventilation
Psychrometrics
Psychrometric Calculator
Moist air properties from dry bulb and one secondary condition — RH, wet bulb, or dew point. Enthalpy, humidity ratio, specific volume, and more.
Psychrometrics
Dew Point Calculator
Magnus formula dew point, Sprung wet-bulb, humidity ratio, enthalpy, and condensation risk on 6 common HVAC surfaces.
Psychrometrics
Wet Bulb / Dry Bulb / RH
Three input modes: DB+RH, DB+WB (Sprung), or DB+DP. Outputs all 6 psychrometric state variables including enthalpy and humidity ratio.
Psychrometrics
Enthalpy Calculator
Enthalpy and humidity ratio for two air states with ΔH and ΔW delta. Full formula display. Instant live calculation.
Psychrometrics
Humidity Ratio Calculator
W in gr/lb, lb/lb, and g/kg from DB + RH. Dew point, partial pressure, specific humidity, and comfort zone check.
Psychrometrics
Coil Leaving Air Calculator
LAT, leaving humidity ratio, and tons from entering conditions, CFM, and SHR. Altitude-corrected. Frost risk and undersized coil alerts.
Psychrometrics
Equipment & Systems
Cooling Coil Calculator
Calculate sensible, latent, and total coil capacity from entering and leaving air conditions. Outputs tons, BTU/h, SHR, water removed, and face velocity.
Equipment
Boiler Size Estimator
Rule-of-thumb boiler output sizing from building area, type, and climate. Includes DHW load, piping loss, and sizing factor for early feasibility.
Equipment
Chiller Size Estimator
Peak cooling load and chiller plant sizing from building area, type, and climate. Diversity factor, redundancy, CHW GPM, and kW output.
Equipment
Equipment Load Split
Split cooling, heating, or flow loads across multiple units. N+1 / N+2 / N×2 redundancy strategies with draft equipment schedule.
Equipment
System Type Recommender
Rule-based HVAC system selector. Answer 6 questions about building type, size, climate, zones, and priority — get top 3 ranked recommendations.
Systems
Natural Gas Pipe Sizer
Capacity-based gas pipe sizing using the Spitzglass and Weymouth formulas. Supports natural gas and propane at low and medium pressure.
Gas Piping
Gas Pipe Quick Estimator
Spitzglass low-pressure sizing for natural gas and propane. Schedule 40 black iron pipe with full capacity table and velocity check.
Gas Piping
Refrigerant Pipe Sizer
Size suction, discharge, and liquid lines for DX systems. Supports R-410A, R-22, R-32, R-407C, and R-134a with velocity-based ACR copper sizing.
Refrigeration
Refrigerant Line Sizer
Velocity-based ACR copper tube sizing for suction, discharge, and liquid lines. Supports R-410A, R-22, R-32, and R-134a.
Refrigeration
Motor Full Load Amp Calculator
Calculate FLA, NEC wire sizing, and breaker size for single and three-phase motors.
Electrical
Conversions & Reference
CFM / Tons / BTU Converter
Live bidirectional converter: tons ↔ BTU/hr ↔ kW ↔ MBH ↔ CFM. Edit any field to update all others instantly.
Conversions
HVAC Unit Conversions
Live bidirectional converters for temperature, airflow, water flow, pressure, energy, and power. Edit any field to update all.
Conversions
Energy Cost Estimator
Annual fan/pump and cooling energy costs. VFD savings via affinity law (power ∝ speed³), simple payback, and kWh breakdown.
Economics
Design Sanity Checker
Paste in tons, CFM, MBH, and GPM — get instant pass/warn/fail flags against rule-of-thumb benchmarks for 8 building types.
QA
Rule-of-Thumb Checker
Quick-reference tables for HVAC rules of thumb — duct velocities, hydronic ΔT, load densities, equipment efficiencies, psychrometric factors.
Reference
VFD Energy Savings Calculator
Calculate motor energy savings from a variable frequency drive using the affinity law cube relationship.
Economics
Simple Payback & ROI
Calculate simple payback, NPV, and lifetime savings for HVAC energy efficiency projects.
Economics
Need more than a calculator?
The AI Design Assistant runs full thermal load calculations, ASHRAE ventilation design, equipment selection, compliance checks, and PDF reports — with Claude AI built in to guide your design decisions.