# HVACLogic — Engineering-Grade HVAC & Building Science Calculators
> Verified deterministic thermodynamic formulas, air distribution physics, refrigerant cycle diagnostics, and heat transfer equations. Governed by ASHRAE, ACCA, SMACNA, and EPA engineering standards. 100% client-side, zero tracking, open-access.

- Canonical Website: https://hvaclogic.org
- Full Mathematical Specifications: https://hvaclogic.org/llms-full.txt
- Climatic Design Conditions: https://hvaclogic.org/ashrae-climatic-data
- Calculation Methodology: https://hvaclogic.org/methodology
- Peer-Reviewed Sources & Codes: https://hvaclogic.org/sources
- Verified Monograph & DOI: https://archive.org/details/power-lab-deterministic-clean-energy-modeling-framework-2026_20260826

## Engineering Pillars & Calculator Directory

### [Digital Ductulator & Air Duct Sizing Tool](https://hvaclogic.org/calculators/ductulator)
- **Route**: `/calculators/ductulator`
- **Pillar**: Airflow & Ducts (`airflow-ducts`)
- **Governing Standards**: ASHRAE, SMACNA, ACCA
- **Description**: Free online ductulator for HVAC engineers. Size round, rectangular & oval ducts via equal friction (Colebrook-White). Real-time 2D visualizer.
- **Primary Keywords**: ductulator, duct sizing calculator, mcquay duct sizer, air duct design calculator
- **Key Capabilities**:
  - Equal friction round diameter and velocity calculation
  - Huebscher rectangular duct equivalence with aspect ratio locking
  - Flexible duct installation sag and compression derating (0% to 30%)
  - SMACNA acoustic noise limits and residential velocity alerts
  - Real-time 2D Canvas cross-section with velocity gradient visualization

### [Flexible Duct CFM & Friction Drop Chart](https://hvaclogic.org/calculators/flex-duct-cfm-chart)
- **Route**: `/calculators/flex-duct-cfm-chart`
- **Pillar**: Airflow & Ducts (`airflow-ducts`)
- **Governing Standards**: ACCA, ASHRAE
- **Description**: Interactive flexible duct CFM chart for 4" to 20" round ducts. Compare airflow across 0.05 to 0.15 in. wg friction rates with sag and compression derating.
- **Primary Keywords**: flex duct cfm chart, flex duct cfm chart, flexible duct air flow chart, 6 flex duct cfm
- **Key Capabilities**:
  - Interactive CFM capacity matrix for diameters 4" through 20"
  - Simultaneous comparison across 0.05, 0.08, 0.10, and 0.15 in.wg friction rates
  - Dynamic sag slider adjusting capacity for 0%, 4%, 15%, and 30% compression
  - One-click printable 1-page PDF reference card for truck clipboards

### [HVAC CFM & Airflow Calculator](https://hvaclogic.org/calculators/cfm-calculator)
- **Route**: `/calculators/cfm-calculator`
- **Pillar**: Airflow & Ducts (`airflow-ducts`)
- **Governing Standards**: ASHRAE, ACCA
- **Description**: Calculate HVAC airflow (CFM) from duct size, air velocity (FPM), sensible heat load (1.08 × ΔT), or room ACH. Free client-side precision.
- **Primary Keywords**: air duct cfm calculator, cfm calculator hvac, cfm chart for duct, sensible heat airflow
- **Key Capabilities**:
  - Sensible heat airflow method: CFM = BTU / (1.08 * Delta T)
  - Velocity and duct cross-section method: CFM = Velocity * Area
  - Room Air Changes per Hour (ACH) turnover calculator
  - Cooling tonnage standard rule (350 to 450 CFM/ton)
  - Direct 1-click workflow handoff to the Digital Ductulator

### [Kitchen Range Hood CFM & Make-Up Air Sizer](https://hvaclogic.org/calculators/kitchen-hood-cfm)
- **Route**: `/calculators/kitchen-hood-cfm`
- **Pillar**: Airflow & Ducts (`airflow-ducts`)
- **Governing Standards**: HVI, IRC, ASHRAE
- **Description**: Calculate required kitchen range hood CFM for gas and electric cooktops. Check mandatory IRC Section M1503.6 make-up air code requirements.
- **Primary Keywords**: kitchen hood cfm calculator, range hood cfm calculator, range hood make up air, how many cfm for range hood
- **Key Capabilities**:
  - Gas cooktop BTU method (100 CFM per 10k BTU) vs electric linear width method
  - Wall-mount vs island hood open-air capture penalty multiplier (1.30x)
  - Equivalent duct length and static pressure friction estimation
  - Automatic IRC M1503.6 make-up air code alerts for exhaust > 400 CFM
  - Recommended round rigid duct diameter sizing (6", 7", 8", 10")

### [Duct Friction Loss & Total Equivalent Length (TEL) Sizer](https://hvaclogic.org/calculators/duct-friction-loss-calculator)
- **Route**: `/calculators/duct-friction-loss-calculator`
- **Pillar**: Airflow & Ducts (`airflow-ducts`)
- **Governing Standards**: ACCA, ASHRAE, SMACNA
- **Description**: Calculate ACCA Manual D Total Equivalent Length (TEL), Available Static Pressure (ASP), and Design Friction Rate (FR) for residential HVAC duct design.
- **Primary Keywords**: duct friction loss calculator, duct friction loss calculator, duct tel meaning, what is duct tel
- **Key Capabilities**:
  - ACCA Manual D Appendix 3 fitting accumulator (elbows, takeoffs, dampers, boots)
  - Available Static Pressure (ASP) solver accounting for wet coils, MERV filters, and registers
  - Exact Design Friction Rate (FR = (ASP * 100) / TEL) in.wg per 100 ft
  - Interactive SVG duct system schematic with static pressure drop gradient
  - Optimal vs High-Resistance fitting warnings (e.g. mitered no-vane elbow penalties)

### [MERV Air Filter Sizing & Static Pressure Drop Sizer](https://hvaclogic.org/calculators/filter-sizing-calculator)
- **Route**: `/calculators/filter-sizing-calculator`
- **Pillar**: Airflow & Ducts (`airflow-ducts`)
- **Governing Standards**: ASHRAE, ACCA
- **Description**: Calculate HVAC air filter face velocity (FPM) and static pressure drops across 1-inch, 2-inch, and 4-inch deep MERV 8 to MERV 16 pleated media.
- **Primary Keywords**: merv filter pressure drop calculator, hvac filter size calculator, filter face velocity calculator, merv 13 static pressure drop
- **Key Capabilities**:
  - Face Velocity (FPM = CFM / Area) compliance checks against ASHRAE 52.2 and ACCA Manual D
  - Initial clean static pressure drop and loaded filter resistance curves
  - Media depth derating: 1-inch vs 2-inch vs 4-inch deep pleats (cuts pressure drop up to 62%)
  - Single filter slot vs multi-grille return configurations (e.g. dual return grilles)
  - Interactive SVG air intake filter visualizer with face velocity gauge and pressure drop bar

### [BTU Heating & Cooling Load Calculator](https://hvaclogic.org/calculators/btu-calculator)
- **Route**: `/calculators/btu-calculator`
- **Pillar**: Cooling & Loads (`cooling-loads`)
- **Governing Standards**: ACCA, ASHRAE
- **Description**: Estimate whole-home and room heating and cooling loads (BTU/hr and Tons) based on square footage, climate zone, insulation quality, and window exposure.
- **Primary Keywords**: btu calculator, btu estimator, british thermal unit calculator, hvac load calculator
- **Key Capabilities**:
  - Sensible and latent cooling load breakdown (BTU/hr and Tons)
  - Climate zone design temperature adjustments (Zones 1 through 7)
  - Envelope insulation quality (R-13 to R-21+ walls, R-30 to R-60 ceilings)
  - Window solar heat gain and internal occupant/appliance loads
  - Interactive SVG load distribution donut chart

### [AC Tonnage & Room Capacity Calculator](https://hvaclogic.org/calculators/ac-tonnage-calculator)
- **Route**: `/calculators/ac-tonnage-calculator`
- **Pillar**: Cooling & Loads (`cooling-loads`)
- **Governing Standards**: ACCA, AHRI
- **Description**: Match room and home square footage to required air conditioning tonnage (1.5 to 5.0 Tons) with regional climate adjustments and SEER2 operating cost modeling.
- **Primary Keywords**: btus ac, aircon capacity, aircon cooling capacity, ac tonnage calculator
- **Key Capabilities**:
  - Square footage to AC tonnage matching (100 to 6,000 sq ft)
  - Regional climate multipliers (Mild, Moderate, Hot/Humid, Extreme Desert)
  - SEER2 operating cost estimator comparing 10-SEER to 20+ SEER2 inverters
  - Nominal airflow CFM requirement matching (400 CFM/ton)

### [HVAC Model Number Tonnage Decoder](https://hvaclogic.org/calculators/ac-model-decoder)
- **Route**: `/calculators/ac-model-decoder`
- **Pillar**: Cooling & Loads (`cooling-loads`)
- **Governing Standards**: AHRI
- **Description**: Decode Carrier, Trane, Lennox, Goodman, Rheem, Daikin & ICP model numbers. Instant nominal tonnage, SEER rating, manufacture year, and CFM airflow.
- **Primary Keywords**: how to find ac tonnage, how to find ac tonnage, carrier nomenclature tonnage, carrier tonnage by model number
- **Key Capabilities**:
  - Regex parser for Carrier, Bryant, Trane, American Standard, Lennox, Goodman, Amana, Rheem, Ruud, and York
  - Instant nominal capacity detection (18 = 1.5T, 24 = 2.0T, 30 = 2.5T, 36 = 3.0T, 42 = 3.5T, 48 = 4.0T, 60 = 5.0T)
  - Recommended nominal airflow CFM output
  - Interactive visual guide for locating condenser and air handler data plates

### [Mini-Split Multi-Zone Sizing Calculator](https://hvaclogic.org/calculators/mini-split-sizing)
- **Route**: `/calculators/mini-split-sizing`
- **Pillar**: Cooling & Loads (`cooling-loads`)
- **Governing Standards**: AHRI, ACCA
- **Description**: Size multi-zone ductless mini-split systems. Match room heat loads to indoor wall/cassette heads (6k to 24k BTU) and outdoor multi-port condensers.
- **Primary Keywords**: mini split sizing calculator, ductless mini split sizing, multi zone mini split sizing, mini split btu calculator
- **Key Capabilities**:
  - Dynamic multi-room builder for up to 6 custom heating & cooling zones
  - Individual indoor head matching (6k, 9k, 12k, 18k, 24k BTU)
  - Outdoor multi-port inverter condenser sizing (18k to 48k BTU / 1.5 to 4.0 Tons)
  - Inverter diversity & over-subscription ratio gauge (100%–130% optimal connected capacity)
  - Live interactive multi-room floor plan lineset schematic visualizer

### [Target Superheat & Subcooling Charging Calculator](https://hvaclogic.org/calculators/superheat-subcooling-calculator)
- **Route**: `/calculators/superheat-subcooling-calculator`
- **Pillar**: Field Diagnostics (`field-diagnostics`)
- **Governing Standards**: EPA, AHRI, ACCA
- **Description**: Calculate target superheat (fixed orifice) and target subcooling (TXV) across R-454B, R-32, R-410A, and R-22 with EPA fault isolation guidance.
- **Primary Keywords**: superheat calculator, subcooling calculator, hvac charging calculator, refrigerant charging diagnostic
- **Key Capabilities**:
  - Dual mode: Fixed Orifice Target Superheat & TXV Target Subcooling
  - NIST REFPROP-referenced PT data for R-454B, R-32, R-410A, R-22, R-134a, R-404A, R-407C
  - Zeotropic glide handling (discrete Bubble/Dew curves for R-454B and R-407C)
  - Color-coded diagnostic indicator with investigative action checklists
  - A2L refrigerant safety callouts and EPA Section 608 boundary checks

### [Digital Refrigerant Pressure-Temperature Chart](https://hvaclogic.org/calculators/pt-chart)
- **Route**: `/calculators/pt-chart`
- **Pillar**: Field Diagnostics (`field-diagnostics`)
- **Governing Standards**: NIST, EPA, ASHRAE
- **Description**: Interactive digital Pressure-Temperature chart for R-454B, R-32, R-410A, R-22 and 30+ refrigerants. Instant bubble and dew point saturation curves for 2026 A2L.
- **Primary Keywords**: pt chart, 454b pt chart, refrigerant pt chart, 454b pressure temperature chart
- **Key Capabilities**:
  - Interactive pressure slider (0 to 650 psig) with instant saturation temperature output
  - Support for 2025/2026 EPA A2L transition refrigerants (R-454B Opteon XL41, R-32)
  - Discrete Bubble Point (liquid) and Dew Point (vapor) curves for zeotropic blends
  - Unit toggle: psig, psia, bar, kPa <-> °F, °C

### [Psychrometric Chart & Moist Air Calculator](https://hvaclogic.org/calculators/psychrometric-calculator)
- **Route**: `/calculators/psychrometric-calculator`
- **Pillar**: Field Diagnostics (`field-diagnostics`)
- **Governing Standards**: ASHRAE
- **Description**: Calculate moist air thermodynamic properties from any 2 inputs (Dry Bulb, Wet Bulb, Dew Point, RH, Enthalpy) with altitude barometric compensation.
- **Primary Keywords**: psychrometric calculator, psychrometric chart calculator, moist air properties, dew point calculator
- **Key Capabilities**:
  - Calculates complete thermodynamic state point from any 2 input parameters (DB + RH, DB + WB, DB + DewPoint)
  - Barometric pressure adjustment based on altitude elevation (-1,000 to 15,000 ft)
  - Outputs: Humidity Ratio (grains/lb), Enthalpy (BTU/lb), Specific Volume, Air Density, and Vapor Pressure
  - Interactive SVG psychrometric state chart with saturation curve and comfort zone boundary
  - ASHRAE Standard 55 thermal comfort zone classification

### [Refrigerant Line Set Charge & Weigh-In Calculator](https://hvaclogic.org/calculators/refrigerant-charge-calculator)
- **Route**: `/calculators/refrigerant-charge-calculator`
- **Pillar**: Field Diagnostics (`field-diagnostics`)
- **Governing Standards**: EPA, ASHRAE
- **Description**: Estimate the manufacturer-specified initial refrigerant weigh-in adjustment for R-454B, R-32, and R-410A line sets using sourced OEM profiles.
- **Primary Keywords**: refrigerant charge calculator, line set charge calculator, additional refrigerant calculator, r454b charge calculator
- **Key Capabilities**:
  - Versioned OEM charging profiles with exact source and model-family scope
  - R-454B, R-32, and R-410A initial line-set weigh-in calculations
  - Custom OEM-rate mode for equipment manuals not included in the profile library
  - Factory allowance, line-size, length, and vertical-limit validation
  - Final-charge verification handoff to superheat and subcooling diagnostics

### [Heat Pump Sizing & Balance Point Tool](https://hvaclogic.org/calculators/heat-pump-size-calculator)
- **Route**: `/calculators/heat-pump-size-calculator`
- **Pillar**: Heating Systems (`heating-systems`)
- **Governing Standards**: ASHRAE, AHRI, ACCA
- **Description**: Calculate heat pump thermal balance point, cold-climate low-ambient heating capacity (47°F, 17°F, -5°F), and auxiliary electric backup heat strip sizing.
- **Primary Keywords**: heat pump size calculator, heat pump sizing, cold climate heat pump sizing, heat pump balance point
- **Key Capabilities**:
  - Thermal balance point intersection between building heat loss and heat pump output
  - Low-ambient inverter heating derate curves (Cold-Climate ccASHP vs Standard Inverter vs Single-Stage)
  - Auxiliary electric backup heat strip requirement sizing (kW)
  - ACCA Manual S cooling oversizing compliance verification
  - Interactive 10-point temperature performance curve matrix

### [Furnace Sizing & AFUE Efficiency Calculator](https://hvaclogic.org/calculators/furnace-size-calculator)
- **Route**: `/calculators/furnace-size-calculator`
- **Pillar**: Heating Systems (`heating-systems`)
- **Governing Standards**: ACCA, AHRI, DOE
- **Description**: Calculate required furnace input and output BTU based on home square footage, climate zone, and AFUE efficiency (80% vs 96% condensing).
- **Primary Keywords**: furnace size calculator, furnace btu calculator, what size furnace do i need, gas furnace sizing
- **Key Capabilities**:
  - Input vs. Output BTU calculation with 80% to 98% AFUE efficiency selector
  - 5-zone regional US climate load modeling (30 to 60 BTU/sq ft)
  - Envelope modifiers for ceiling height (8ft to 24ft) and insulation grades
  - Nominal furnace model matching (40k, 60k, 80k, 100k, 120k BTU) and cabinet width
  - Required blower airflow CFM verification (CFM = Output / (1.08 * Delta T))

### [Hydronic Boiler & Baseboard Sizing Calculator](https://hvaclogic.org/calculators/boiler-size-calculator)
- **Route**: `/calculators/boiler-size-calculator`
- **Pillar**: Heating Systems (`heating-systems`)
- **Governing Standards**: ASHRAE, AHRI
- **Description**: Size residential hydronic heating boilers based on fin-tube baseboard linear footage, cast-iron radiator EDR, and indirect domestic hot water priority.
- **Primary Keywords**: boiler size calculator, hydronic heating calculator, baseboard sizing, radiator edr calculator
- **Key Capabilities**:
  - Multi-method sizing engine: Fin-Tube Baseboard linear feet, Cast-Iron Radiator EDR, or Heat Loss (BTU/hr)
  - Hot water vs low-pressure steam rating conversion (150 vs 240 BTU/hr per sq ft EDR)
  - Domestic Hot Water (DHW) indirect tank pickup with priority zone controller override
  - I=B=R and AHRI Net Rating piping/pickup factors (1.15x water / 1.33x steam)
  - Interactive SVG hydronic piping loop schematic with boiler, expansion tank, and circulator
  - 1-Click CSV engineering submittal export

### [Garage & Workshop Heater Sizing Calculator](https://hvaclogic.org/calculators/garage-heater-sizing)
- **Route**: `/calculators/garage-heater-sizing`
- **Pillar**: Heating Systems (`heating-systems`)
- **Governing Standards**: ASHRAE, ACCA
- **Description**: Size gas unit heaters, forced-air electric heaters, and radiant tubes for 1 to 3-car garages. ACCA Manual J & ASHRAE heat loss with slab insulation derating.
- **Primary Keywords**: garage heater sizing calculator, shop heater sizing, garage heater btu calculator, electric garage heater sizing
- **Key Capabilities**:
  - 1-car, 2-car, 2.5-car, 3-car, and custom pole barn shop dimension geometry
  - Concrete uninsulated slab edge perimeter conduction and overhead door thermal losses
  - Gas unit heater (30k–125k BTU/hr) vs electric forced-air (3kW–20kW / 240V Amps) recommendations
  - Interactive SVG garage cross-section visualizer with ceiling throw cone and heat loss flow vectors
  - Freeze-protection (50°F) vs active workshop comfort (65°F) setpoint modes

### [Combustion Air & Confined Space Sizer (NFPA 54 / IFGC)](https://hvaclogic.org/calculators/combustion-air-calculator)
- **Route**: `/calculators/combustion-air-calculator`
- **Pillar**: Heating Systems (`heating-systems`)
- **Governing Standards**: NFPA, IFGC, ASHRAE
- **Description**: Size mechanical room combustion air openings per NFPA 54 and IFGC. Instant 50 cu ft/1,000 BTU confined space test and indoor/outdoor louver duct sizing.
- **Primary Keywords**: combustion air calculator, nfpa 54 combustion air, confined space combustion air, furnace combustion air requirements
- **Key Capabilities**:
  - NFPA 54 & IFGC standard 50 cu ft per 1,000 BTU/hr confined space threshold test
  - Multi-appliance gas input load accumulator (furnaces, boilers, water heaters, unit heaters)
  - 4 standard NFPA 54 combustion air methods (Indoor 2 openings, Outdoor vertical 2 openings, Outdoor horizontal 2 openings, Outdoor single opening)
  - Louver free area derating (Metal 75% vs Wood 25%) and round duct diameter sizing
  - Interactive SVG mechanical room visualizer with upper/lower air intake ducts and volume gauge

### [Insulation R-Value & U-Factor Calculator](https://hvaclogic.org/calculators/r-value-calculator)
- **Route**: `/calculators/r-value-calculator`
- **Pillar**: Building Science (`building-science`)
- **Governing Standards**: IECC, ASHRAE
- **Description**: Build multi-layer wall, roof, and floor assemblies to calculate total R-value (R-total) and overall U-factor with IECC 2021/2024 climate zone compliance checks.
- **Primary Keywords**: r value for insulation, r value calculator, u factor calculator, thermal resistance
- **Key Capabilities**:
  - Dynamic multi-layer assembly builder (siding, continuous foam, sheathing, cavity batt/spray foam, drywall, air films)
  - Total assembly thermal resistance R-total and overall U-factor (U = 1 / R_total)
  - IECC 2021 / 2024 Energy Code prescriptive minimum compliance checks (Climate Zones 1 to 7)
  - Interactive SVG cross-section visualizer showing thermal textures and indoor-to-outdoor temperature gradient
  - Annual heat loss transmission estimator (BTU/sq ft per year)

### [Building Heat Loss & Infiltration Calculator](https://hvaclogic.org/calculators/heat-loss-calculator)
- **Route**: `/calculators/heat-loss-calculator`
- **Pillar**: Building Science (`building-science`)
- **Governing Standards**: ASHRAE, ACCA
- **Description**: Calculate whole-building peak heat loss combining envelope conductive transmission (U * A * Delta T) and blower door air infiltration leakage.
- **Primary Keywords**: heat loss calculator, building heat loss calculator, heat loss estimator, home heat loss calculator
- **Key Capabilities**:
  - Conductive transmission heat loss solver across walls, ceilings, windows, doors, and foundation slabs
  - Air infiltration heat loss modeling using natural air changes per hour (ACHnat) and CFM leakage
  - Interactive SVG heat loss donut chart and envelope component percentage distribution
  - Heating equipment sizing recommendations (Furnace BTU/hr and Heat Pump Tonnage)
  - 1-Click CSV engineering report submittal export


## Standard Engineering Constants & Reference Baseline
- Standard Air Density (\rho_0): 0.075 lb/ft³ at 70°F (21.1°C), 14.696 psia (101.325 kPa)
- Sensible Heat Constant (C_p \times \rho \times 60): 1.08 BTU/(hr·CFM·°F) at sea level
- Total Heat / Enthalpy Constant (\rho \times 60): 4.50 BTU/(hr·CFM·(BTU/lb))
- Latent Heat Constant: 0.68 BTU/(hr·CFM·gr/lb)
- Latent Heat of Vaporization (Water at 70°F): 1,061 BTU/lb
- Water Heat Capacity Rate: 500 BTU/(hr·GPM·°F) (for pure water at 8.33 lb/gal)
- Atmospheric Pressure vs Altitude (P_alt): P_0 \times (1 - 6.8754 \times 10^{-6} \times h)^{5.2559} psia