Engineering Calculators
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Coil Selection Calculator
RELATED CALCULATORS
Instructions:
Review the methodology below to ensure it aligns with your project's requirements.
BTUH Capacity & Leaving Air Temperature
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Review the methodology below to ensure it aligns with your project's requirements.
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Select US or Metric Units
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Sensible Cooling:
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Select the parameter for which to solve: Sensible Cooling, Volume Flow Rate, Leaving air Temperature, or Entering Air Temperature.
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Enter all of the required inputs.
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Click the Calculate button, and the Result will show below the table.
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Total Cooling:
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Select the parameter for which to solve: Total Cooling, Volume Flow Rate, Leave air Enthalpy, or Entering Air Enthalpy (note there is a Calculate Enthalpy button to take you to our Psychrometric Calculator to solve for Enthalpy).
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Enter all of the required inputs.
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Click the Calculate button, and the Result will show below the table.
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Latent Cooling
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Select the parameter for which to solve: Latent Cooling, Volume Flow Rate, Leave air Humidity Ratio, or Entering Air Humidity Ratio (note there is a Calculate Humidity Ratio button which will take you to our Psychrometric Calculator to solve for Humidity Ratio).
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Enter all of the required inputs.
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Click the Calculate button, and the Result will show below each table.
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Area & Velocity
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Review the methodology below to ensure it aligns with your project's requirements.
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Select US or Metric Units
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Enter coil face dimensions (height and width)
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Enter airflow (CFM or L/s).
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Click Calculate to display coil face area and air velocity.
Water and Glycol Flow
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Review the methodology below to ensure it aligns with your project's requirements.Select US or Metric Units
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Select the parameter for which to solve: Fluid Capacity, Volume Flow Rate, Entering Temperature, or Leaving Temperature.
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Enter all of the required inputs.
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Click the calculate button, and the Result will show below the table.
Water Velocity
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Review the methodology below to ensure it aligns with your project's requirements.Select US or Metric Units
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Select US or Metric Units
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Enter flow rate, tube diameter, and number of tubes.
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Click the calculate button, and the Result will show below the table.
BTUH Capacity & Leaving Air Temperature – Methodology
Overview
This calculator estimates sensible, total, and latent cooling capacities of HVAC air-handling systems using fundamental heat transfer and psychrometric principles. It is designed for engineers and designers to quickly verify equipment performance, airflow adequacy, and energy loads based on entering and leaving air conditions.
Calculations are consistent with ASHRAE Fundamentals (2021), Chapter 1 & 17, and ACCA Manual N (2020) methods.
1. Sensible Cooling (Dry Bulb Method)
Formula:
Q_s = 1.08 x CFM x (T_enter - T_leave)
Where:
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( Q_s ) = Sensible cooling load (Btu/h)
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( CFM ) = Volume flow rate of air (ft³/min)
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( T_{enter} ), ( T_{leave} ) = Entering and leaving dry bulb temperatures (°F)
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1.08 = Constant incorporating air density (0.075 lb/ft³) × specific heat (0.24 Btu/lb·°F) × 60 min/h
Example:
Given: CFM = 2,000 CFM
T_enter = 95°F
T_leave = 55°F
Q_s = 1.08 x 2000 x (95 - 55) = 86,400 Btu/h
Result match calculator results of: 85,968 Btu/h (rounding difference ≤1%).
2. Total Cooling (Enthalpy Method)
Formula:
Q_t = 4.5 x CFM x (h_enter - h_leave)
Where:
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Q_t = Total cooling load (Btu/h)
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h_enter = Entering air enthalpy (Btu/lb)
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h_leave= Leaving air enthalpy (Btu/lb)
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4.5 = Constant derived from ( 0.075 lb/ft³ x 60 min/h )
Example:
Given: h_enter = 40.28 Btu/lb
h_leave = 22.87 Btu/lb
CFM = 2000 CFM
Q_t = 4.5 x 2000 x (40.28 - 22.87) = 156,690 Btu/h
Result match calculator results.
3. Latent Cooling (Humidity Ratio Method)
Formula:
Q_L = 4840 x CFM x (W_enter - W_leave)
Where:
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Q_L = Latent cooling load (Btu/h)
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W_enter = Entering humidity ratios (grains/lb dry air)
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W_leave = Leaving humidity ratios (grains/lb dry air)
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4840 = Conversion factor from grains to Btu/h at standard air density
Example:
Given: W_enter = 110.93 grains/lb dry air
W_leave = 62.38 grains/lb dry air
CFM = 2000 CFM
Q_L = 4840 x 2000 x (110.93 - 62.38) / 7000 = 67,138 Btu/h
Result match calculator results.
4. Relationships Between Cooling Components
[Q_t = Q_s + Q_L]
This relationship can be used to validate system performance or cross-check calculated results.
5. Reference Standards
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ASHRAE Fundamentals Handbook (2021) — Chapters 1, 17, and 36
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ACCA Manual N (2020) — Commercial Load Calculation Procedures
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Carrier System Design Manual, Part 2 (2009) — Air Conditioning Load Estimation
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ASHRAE 62.1-2022 — Ventilation for Acceptable Indoor Air Quality
7. Application Notes
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Use psychrometric charts or the Adicot Psychrometric Calculator for enthalpy and humidity ratio.
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Confirm all values at standard atmospheric conditions (14.7 psia, 70°F).
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For SI conversions:
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1 Btu/h = 0.293 W
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1 CFM = 0.472 L/s
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Disclaimer:
This calculator is intended for educational and preliminary design use only. Results should be validated using manufacturer coil performance data and ASHRAE-approved engineering procedures.
Coil Face Area & Air Velocity – Methodology
Overview
This calculator determines the coil face area and air velocity across an HVAC cooling or heating coil based on the coil’s physical dimensions and volumetric airflow rate.
These parameters are essential for evaluating coil performance, fan sizing, and condensation control. Excessive face velocity may cause water carryover or noise, while low velocity may reduce heat transfer efficiency.
Calculations are consistent with ASHRAE Fundamentals (2021), Chapter 21: Airflow and Duct Design, and ACCA Manual D (2014) standards for residential and light commercial air distribution systems.
1. Coil Face Area
Formula:
A = H x L
Where:
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( A ) = Coil face area (ft² or m²)
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( H ) = Coil face height (ft or m)
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( L ) = Coil face length (ft or m)
Unit Conversions:
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For Imperial units:
A = ( H x L) / 12
where height and length are entered in inches
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For Metric units:
A = ( H x L ) / 1,000,000
where height and length are entered in millimeters.
2. Coil Air Velocity
Formula:
V = Q / A
Where:
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( V ) = Coil air velocity (fpm or m/s)
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( Q ) = Volumetric flow rate of air (CFM or L/s)
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( A ) = Coil face area (ft² or m²)
Conversions:
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1 CFM = 0.0004719 m³/s
- 1 L/s = 0.001 m³/s
3. Example (Imperial Units)
Given:
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Height = 12 in
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Length = 12 in
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Airflow = 2,000 CFM
Step 1:
A = 12 / 12 x 12 / 12 = 1.00 ft²
Step 2:
V = 2,000 / 1.00 = 2,000 fpm
✅ Result:
Coil Area = 1.00 ft²
Coil Velocity = 2,000 fpm
4. Example (Metric Units)
Given:
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Height = 250 mm
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Length = 250 mm
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Airflow = 600 L/s
Step 1:
A =250 x 250 / 1,000,000 = 0.0625 m²
Step 2:
V = 600 L/s / 0.0625 m² x 1 m³/s} / 1,000 L/s = 9.6 m/s
✅ Result:
Coil Area = 0.06 m²
Coil Velocity = 9.6 m/s
5. Design Guidance
Parameter Recommended Range Reference
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Cooling coil face velocity 2.0–2.5 m/s (400–500 fpm)ASHRAE Fundamentals (2021), Ch. 21
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Heating coil face velocity 3.0–4.0 m/s (600–800 fpm)ACCA Manual D (2014)
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Maximum allowable to avoid carryover≤ 2.8 m/s (550 fpm)ASHRAE Systems and Equipment (2020)
6. Reference Standards
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ASHRAE Fundamentals Handbook (2021) — Chapter 21: Duct Design and Airflow Principles
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ASHRAE HVAC Systems and Equipment (2020) — Section: Coil Design and Performance
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ACCA Manual D (2014) — Residential Duct Systems
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Carrier System Design Manual, Part 2 (2009) — Air Distribution and Coil Selection
7. Application Notes
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Maintain coil velocities within recommended ranges to prevent condensate blow-off.
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Ensure coil face area aligns with fan capacity and static pressure limitations.
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For multi-row coils, use the total effective face area rather than finned area for calculations.
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Use psychrometric tools to confirm leaving air conditions at calculated velocities.
Disclaimer:
This calculator is intended for educational and preliminary design use only. Results should be validated using manufacturer coil performance data and ASHRAE-approved engineering procedures.
Water & Glycol Flow Rate – Methodology
Overview
This calculator estimates the required volumetric flow rate (or heat load, or entering/leaving temperatures) for hydronic systems using water or glycol solutions.
It applies fundamental energy balance equations for sensible heat transfer and allows for different heat capacities of glycol mixtures commonly used in HVAC chilled- and hot-water loops.
Calculations are consistent with ASHRAE Fundamentals (2021), Chapter 4: Heat Transfer and Fluid Flow, and ACCA Manual N (2020) methods for coil and piping design.
1. Formula – Energy Balance
Q=V˙×cp×ΔTQ = V˙ x cp x Δ T
Where:
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Q = Heat load (Btu/h or kW)
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V˙ = Volumetric flow rate (GPM or L/s)
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cp = Specific heat capacity × density × 60 (Fluid factor)
(Btu/h)/(GPM·°F) or kJ/(L·°C) -
ΔT = Temperature difference (Entering – Leaving)
Rearranged to solve for flow rate:
V˙=cp×ΔTQ
2. Typical Fluid Factors (cₚ)
Fluid English (Btu/h per GPM·°F) Metric (kJ per L·°C)
Ethylene Glycol 10% 483.9067 4.044983
Ethylene Glycol 20% 466.4925 3.899572
Ethylene Glycol 30% 448.6578 3.750662
Ethylene Glycol 40% 430.4026 3.598254
Ethylene Glycol 50% 411.7268 3.442348
Propylene Glycol 10% 487.3791 4.073503
Propylene Glycol 20% 473.7561 3.959300
Propylene Glycol 30% 460.0313 3.844288
Propylene Glycol 40% 446.2047 3.728467
Propylene Glycol 50% 432.2765 3.611836
Water 500.9004 4.186895
Values assume 60 °F (15 °C) mean temperature per ASHRAE 2021, Table 4-2.
3. Example (English Units)
Given:
Heat Load = 9,500 Btu/h
Entering = 80 °F
Leaving = 54 °F
Fluid = Propylene Glycol 40 % → cp=446.2
ΔT=80−54=26°F
V˙=9,500 / (446.2×26) =0.82GPM
✅ Result: Volumetric Flow Rate = 0.82 GPM
4. Example (Metric Units)
Given:
Heat Load = 1,500 kW
Entering = 23 °C
Leaving = 16 °C
Fluid = Water → cp=4.2
ΔT=7°C
V˙=1,500 / (4.2×7) =51.0L/s
✅ Result: Volumetric Flow Rate = 51.0 L/s (≈ 184 m³/h)
5. Application Notes
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Maintain proper fluid selection for freeze protection and corrosion control.
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Adjust flow for glycol concentration: higher glycol → lower cₚ → higher flow requirement.
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Design flow velocity in piping:
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Chilled water: 1.5 – 3.0 m/s (5 – 10 ft/s)
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Hot water: 1.0 – 2.5 m/s (3 – 8 ft/s)
(Ref: ASHRAE HVAC Systems and Equipment, 2020)
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6. Reference Standards
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ASHRAE Fundamentals Handbook (2021) — Ch. 4 Heat Transfer and Fluid Flow; Ch. 32 Hydronic System Design
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ASHRAE HVAC Systems & Equipment (2020) — Hydronic Heating and Cooling Systems
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ACCA Manual N (2020) — Commercial Load Calculations
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Carrier System Design Manual, Part 3 (2012) — Hydronic Coil and Piping Design
Disclaimer:
This calculator is intended for educational and preliminary design use only. Results should be validated using manufacturer coil performance data and ASHRAE-approved engineering procedures.
Water Velocity – Methodology
Overview
This calculator determines the average velocity of water or fluid flow through one or more tubes based on the total flow rate, tube inner diameter, and number of parallel tubes.
Maintaining velocity within proper ranges is critical for avoiding erosion, noise, and poor heat transfer performance in hydronic and plumbing systems.
Calculations are consistent with ASHRAE Fundamentals (2021), Chapter 22: Pipe Flow, and ASPE Design Handbook (2017).
1. Formula (English Units)
V=(0.4085 ×Q) / (N×D²)
Where:
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V = Velocity (ft/s)
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Q = Flow rate (GPM)
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N = Number of tubes or parallel circuits
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D = Inside diameter of tube (inches)
2. Formula (Metric Units)
V= (4×Q) / (N×π×D²)
Where:
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V = Velocity (m/s)
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Q = Flow rate (L/s)
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D = Diameter (mm ÷ 1000)
2. Example (English Units)
Given:
Q=1 GPM
D=1 in
N=15
V=(0.4085 ×Q) / (N×D²)
=(0.4085×1 GPM) / (15×(1 in)²)
✅ Result: 0.0272 FPS
3. Example (Metric Units)
Given:
Q=2.0 L/s
D=25 mm
N=2
V=4×2.0 / [2×π×(0.025)²]
✅ Result: 2.04 m/s
4. Design Guidelines
Fluid System Velocity Range Notes
Chilled Water 2–5 ft/s (0.6–1.5 m/s) Avoid air binding & ensure good heat transfer
Condenser Water 3–6 ft/s (0.9–1.8 m/s) Prevent scaling
Glycol Mixtures 2.5–5 ft/s (0.75–1.5 m/s) Higher viscosity; lower Reynolds number
Domestic Water 3–8 ft/s (0.9–2.5 m/s) Minimize noise & corrosion
5. Reference Standards
1. ASHRAE Handbook—Fundamentals, 2021. Chapter 22: Pipe Flow.
2. ASHRAE Handbook—HVAC Systems and Equipment, 2020. Hydronic Piping Systems.
3. ASPE Design Handbook, Volume 2, 2017. Plumbing Systems.
4. Carrier System Design Manual, Part 3, 2012. Pipe Sizing for HVAC Systems.
5. Bell & Gossett Engineering Manual (System Syzer), 2018 Edition.
6. ASHRAE Handbook—HVAC Applications, 2019. Chapter 46: Pipe Sizing.
7. Perry’s Chemical Engineers’ Handbook, 9th Ed., Section 6: Fluid Mechanics and Transport Properties.
6. Application Notes
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Ensure velocity is sufficient to maintain turbulent flow (Re > 4000).
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Limit maximum velocity to reduce pipe erosion and water hammer.
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For multi-tube coils, divide total flow evenly among circuits for accurate results.
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Use appropriate glycol correction factors for viscosity adjustments.
Disclaimer:
This calculator is intended for educational and preliminary design use only. Results should be validated using manufacturer coil performance data and ASHRAE-approved engineering procedures.