How to use it

Review the methodology below to make sure it aligns with your project's requirements, then choose US or metric units. Each of the four tools gives its result as soon as its own inputs are complete.

1. Coil air side (sensible, latent and total cooling)

For the entering air and the leaving air, choose whether you know its moisture as a wet bulb, a relative humidity or a dew point. The two can differ, for example an RH entering and a dew point leaving.
Enter the entering and leaving dry bulb, and the entering and leaving wet bulb, RH or dew point.
Enter the airflow (at the entering air), and the altitude if the project is not near sea level.
The results give each condition's enthalpy and humidity ratio, the sensible, latent and total cooling, and the sensible heat ratio.
To size the airflow instead, set "Solve for" to "Airflow for a total cooling load" and enter the total cooling.

2. Coil face area and velocity

Enter the coil face height and width. The face velocity uses the airflow from tool 1.

3. Water and glycol flow

Select the quantity to solve for: heat load, flow rate, entering temperature or leaving temperature.
Select the coil: Cooling (chilled water or glycol, which warms up through the coil) or Heating (hot water, which cools down). This decides which side of the known temperature a solved temperature falls on.
Enter the other inputs. Leave the heat load blank to use the total cooling from tool 1.

4. Water velocity in coil tubes

Enter the tube inside diameter and the number of tubes fed, and the flow rate, or leave it blank to use the flow from tool 3.

BTUH Capacity & Leaving Air Temperature – Methodology

Overview

This tool finds the sensible, latent and total cooling of a coil from its entering and leaving air conditions and the airflow. It uses the exact method of the ASHRAE Handbook—Fundamentals, chapter 1 ("Moist Air Cooling and Dehumidification"), rather than the standard-air factors 1.08, 0.68 and 4.5, so the result follows the actual density of the air at its temperature, humidity and altitude. The psychrometric 2-condition calculator uses the same method, so the two agree.

Air conditions

Each condition's humidity ratio W, enthalpy h and specific volume v come from its dry bulb and its wet bulb, RH or dew point, with the ASHRAE psychrometric equations at the altitude's atmospheric pressure (the same equations as the psychrometric chart calculator).

Mass flow of dry air

m = CFM x 60 / v_enter

m = Mass flow of dry air (lb/h)
CFM = Airflow at the entering air (ft³/min)
v_enter = Specific volume of the entering air (ft³/lb dry air)

Total cooling

Q_t = m x [(h_enter - h_leave) - (W_enter - W_leave) x h_w]

h_enter, h_leave = Entering and leaving enthalpy (Btu/lb dry air)
W_enter, W_leave = Entering and leaving humidity ratio (lb/lb dry air)
h_w = Enthalpy of the condensate, which leaves at the leaving dry bulb: h_w = T_leave - 32 (Btu/lb)

Sensible and latent cooling

Q_s = m x (0.240 + 0.444 x W_leave) x (T_enter - T_leave)

Q_L = Q_t - Q_s

So sensible plus latent always equals the total, and the sensible heat ratio is Q_s / Q_t. The condensate is m x (W_enter - W_leave) lb/h.

Example

Given: 2,000 CFM; entering 95 °F dry bulb, 78 °F wet bulb; leaving 55 °F dry bulb, 54 °F wet bulb; sea level.

Entering: h = 41.30 Btu/lb, W = 0.016771 lb/lb (117.4 gr/lb), v = 14.360 ft³/lb
Leaving: h = 22.57 Btu/lb, W = 0.008631 lb/lb (60.4 gr/lb)
m = 2,000 x 60 / 14.360 = 8,356 lb/h
Q_t = 8,356 x [(41.30 - 22.57) - 0.008140 x 23] = 154,971 Btu/h
Q_s = 8,356 x (0.240 + 0.444 x 0.008631) x (95 - 55) = 81,502 Btu/h
Q_L = 154,971 - 81,502 = 73,469 Btu/h; sensible heat ratio 0.53; condensate 68.0 lb/h

The same airflow by the standard-air shortcuts gives 1.08 x 2,000 x 40 = 86,400 Btu/h sensible and 4.5 x 2,000 x 18.73 = 168,593 Btu/h total, 6 to 9 % high here, because 95 °F humid air is lighter than standard air (14.36 ft³/lb against 13.33). The shortcuts are fine for hand checks near standard conditions; the exact method holds at any condition and altitude.

Solving for airflow

With "Airflow for a total cooling load", the tool inverts the total: CFM = Q_t x v_enter / {60 x [(h_enter - h_leave) - (W_enter - W_leave) x h_w]}.

Reference Standards

ASHRAE Handbook—Fundamentals (2025) — Chapter 1: Psychrometrics
ACCA Manual N, 5th edition — Commercial Load Calculation Procedures
Carrier System Design Manual, Part 2 (2009) — Air Conditioning Load Estimation
ASHRAE 62.1-2025 — Ventilation and Acceptable Indoor Air Quality

Application Notes

Enter the altitude when the project is not near sea level; it sets the atmospheric pressure, and so the air's density and humidity ratio.
Positive loads are cooling; a negative load denotes heating, and a negative latent load denotes adding moisture.
For SI conversions:
1 Btu/h = 0.293 W
1 CFM = 0.472 L/s

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 (2025), Chapter 21: Duct Design, and ACCA Manual D (2016) standards for residential and light commercial air distribution systems.

Coil Face Area

Formula:

A = H x L

Where:

( A ) = Coil face area (ft² or m²)
( H ) = Coil face height (ft or m)
( L ) = Coil face length (ft or m)

Unit Conversions:

For Imperial units:

A = (H x L) / 144

where height and length are entered in inches

For Metric units:

A = ( H x L ) / 1,000,000

where height and length are entered in millimeters.

Coil Air Velocity

Formula:

V = Q / A

Where:

( V ) = Coil air velocity (fpm or m/s)
( Q ) = Volumetric flow rate of air (CFM or L/s)
( A ) = Coil face area (ft² or m²)

Conversions:

1 CFM = 0.0004719 m³/s
1 L/s = 0.001 m³/s

Example (Imperial Units)

Given:

Height = 12 in
Length = 12 in
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

Example (Metric Units)

Given:

Height = 250 mm
Length = 250 mm
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

Design Guidance

Parameter Recommended Range Reference

Cooling coil face velocity 2.0–2.5 m/s (400–500 fpm)ASHRAE HVAC Systems and Equipment (2024), Air-Cooling and Dehumidifying Coils
Heating coil face velocity 3.0–4.0 m/s (600–800 fpm)ACCA Manual D (2016)
Maximum allowable to avoid carryover≤ 2.8 m/s (550 fpm)ASHRAE HVAC Systems and Equipment (2024)

Reference Standards

ASHRAE Handbook—Fundamentals (2025) — Chapter 21: Duct Design
ASHRAE HVAC Systems and Equipment (2024) — Air-Cooling and Dehumidifying Coils
ACCA Manual D (2016) — Residential Duct Systems
Carrier System Design Manual, Part 2 (2009) — Air Distribution and Coil Selection

Application Notes

Maintain coil velocities within recommended ranges to prevent condensate blow-off.
Ensure coil face area aligns with fan capacity and static pressure limitations.
For multi-row coils, use the total effective face area rather than finned area for calculations.
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 (2025), Chapter 4: Heat Transfer, and ACCA Manual N (5th edition) methods for coil and piping design.

Formula – Energy Balance

Q = V̇ × c_p × ΔT

Where:

Q = Heat load (Btu/h or kW)
V˙ = Volumetric flow rate (GPM or L/s)
cp = Specific heat capacity × density × 60 (Fluid factor) (Btu/h)/(GPM·°F) or kJ/(L·°C)
ΔT = Temperature difference between the entering and leaving fluid

Rearranged to solve for flow rate:

V̇ = Q ÷ (c_p × ΔT)

Solving for a temperature, ΔT = Q ÷ (V̇ × c_p). In a cooling coil the fluid warms up, so leaving = entering + ΔT; in a heating coil it cools down, so leaving = entering − ΔT. Temperatures below freezing keep their sign.

Typical Fluid Factors (cₚ)

Fluid English (Btu/h per GPM·°F) Metric (kJ per L·°C)

Ethylene Glycol 10% (by volume) 481.0 4.0219

Ethylene Glycol 20% (by volume) 469.1 3.9224

Ethylene Glycol 30% (by volume) 454.7 3.8019

Ethylene Glycol 40% (by volume) 438.2 3.6638

Ethylene Glycol 50% (by volume) 419.4 3.5071

Propylene Glycol 10% (by volume) 491.1 4.1067

Propylene Glycol 20% (by volume) 483.7 4.0448

Propylene Glycol 30% (by volume) 472.5 3.9510

Propylene Glycol 40% (by volume) 457.7 3.8274

Propylene Glycol 50% (by volume) 439.3 3.6729

Water 500.9 4.1869

Glycol concentrations are by volume. The glycol factors are density × specific heat at 15 °C (59 °F), from ASHRAE Handbook—Fundamentals (2001), Chapter 21, Tables 6, 7, 10 and 11 (the Dow data for inhibited glycols); water is 8.34 lb/gal × 1.001 Btu/lb·°F. The factors change a little with temperature: for hot water, or glycol well below 59 °F, check the density and specific heat at your temperature in ASHRAE Handbook—Fundamentals (2025), Chapter 31, or the manufacturer's data.

Example (English Units)

Given:

Heat Load = 9,500 Btu/h Entering = 80 °F Leaving = 54 °F Fluid = Propylene Glycol 40 % (by volume) → factor = 457.7

ΔT=80−54=26°F

V˙=9,500 / (457.7×26) =0.80GPM

✅ Result: Volumetric Flow Rate = 0.80 GPM

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)

Application Notes

Maintain proper fluid selection for freeze protection and corrosion control.
Adjust flow for glycol concentration: higher glycol → lower cₚ → higher flow requirement.
Design flow velocity in piping:
Chilled water: 1.5 – 3.0 m/s (5 – 10 ft/s)
Hot water: 1.0 – 2.5 m/s (3 – 8 ft/s) (Ref: ASHRAE HVAC Systems and Equipment, 2024)

Reference Standards

ASHRAE Handbook—Fundamentals (2025) — Ch. 4 Heat Transfer; Ch. 31 Physical Properties of Secondary Coolants (Brines)
ASHRAE HVAC Systems and Equipment (2024) — Ch. 32 Hydronic Heating and Cooling
ACCA Manual N, 5th edition — Commercial Load Calculations
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 (2025), Chapter 22: Pipe Design, and ASPE Design Handbook (2017).

Formula (English Units)

V=(0.4085 ×Q) / (N×D²)

Where:

V = Velocity (ft/s)
Q = Flow rate (GPM)
N = Number of tubes or parallel circuits
D = Inside diameter of tube (inches)

Formula (Metric Units)

V= (4×Q) / (N×π×D²)

Where:

V = Velocity (m/s)
Q = Flow rate (L/s ÷ 1000, in m³/s)
D = Diameter (mm ÷ 1000)

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

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

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

Reference Standards
ASHRAE Handbook—Fundamentals, 2025. Chapter 22: Pipe Design.
ASHRAE Handbook—HVAC Systems and Equipment, 2024. Chapter 32: Hydronic Heating and Cooling.
ASPE Design Handbook, Volume 2, 2017. Plumbing Systems.
Carrier System Design Manual, Part 3, 2012. Pipe Sizing for HVAC Systems.
Bell & Gossett Engineering Manual (System Syzer), 2018 Edition.
Perry’s Chemical Engineers’ Handbook, 9th Ed., Section 6: Fluid Mechanics and Transport Properties.
Application Notes

Ensure velocity is sufficient to maintain turbulent flow (Re > 4000).
Limit maximum velocity to reduce pipe erosion and water hammer.
For multi-tube coils, divide total flow evenly among circuits for accurate results.
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.