It is impossible to make a calculator that is both simple and concise while being customizable with state of the art accuracy. With many simple HVAC calculators already available, I choose to emphasize accuracy and customization over simplicity.

In order to display all the necessary data, these calculators are best viewed on a laptop or desktop computer; sorry, but they are not mobile-friendly.

If you should find that a calculator has an error (and have an extra moment), would you mind helping me fix it by sending me a description of the issue, and maybe a screenshot? I will never use your email address for any purpose other than a possible “thank you”!

Ever wondered if a systems LineSet contributed to the demise of its compressor? For residential and light commercial applications, this tool calculates the minimum and maximum acceptable pre-fabricated LineSet tubing sizes (for split systems up to 7.5 tons) that will accommodate correct velocities without excessive pressure drop. Calculations assure oil return without the use of vapor line oil traps (which reduce capacity and efficiency). Credit and thanks goes to Bruce Porter P.E. He provided me the Engineered Factors critical to performing the line size calculations.

This calculator provides notes for when "Long Line" and/or "Maximum Vertical Separation" accessories are recommended by manufactures (at least those who publish line sizing design procedures).

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HVAC Performance Calculator

Based on the Psychrometric and Coil Performance Calculator, this calculator takes a snapshot of the systems current operation and calculates the performance, efficiency and cost

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A.K.A. "Wayne's Brain", a calculator that troubleshoots the refrigeration and air flow of an air conditioner by entering the operating temperatures and pressures. Click "Analyze" to see the results. Find out what is in or out of range. Scroll down for a diagnosis with causes and/or remedies.

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Psychrometric data is not only useful for commercial design, Technicians can also benefit from knowing exactly how a system is performing based on the actual entering and leaving conditions. You can download and print psychrometric charts from Coolerado Cooling.

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This free ductulator calculates the exact duct size (round and rectangular) for the given friction rate, duct type, and amount of airflow. It will automatically adjust the size to keep from exceeding the maximum Manual D velocities for residential duct systems. View a demonstration.

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An inclusive air duct calculator for diameter, velocity, CFM, and pressure drop of various types of duct. It will also determine round duct equivalents for rectangle, flat oval, and elliptical (flattened round) duct.

Duct roughness and air properties are adjustable and includes a metric option.

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A calculating web form for use with the Manual D procedure to determine the friction rate for sizing a residential duct system.

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With the doors closed, the amount of airflow supplied to a room is limited by the amount that will exit from the room. The room becomes pressurized. An over pressurized room will expel conditioned air to the outside, attic, or crawlspace. Use this calculator to determine the minimum effective transfer grille size required to limit the pressure difference between the room and the outside to a maximum of 0.012"wc. Read more on transfer grilles at Building Science Corporation.

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A calculating web form for recording and calculating the Stepwise air balancing process. Enter the outlet description (optional) and the design airflow, click "Calculate" to display the 10% range. Enter the measured value of each outlet and it will tell you the percentage you are over or under, if within 10% it displays "OK".

Balancing a "Rule of Thumb" designed duct system is difficult if not impossible. Balancing is easy when the branch ducts are the size determined by the Manuals J and D procedures. Then only small changes in damper position are required. Typically less than 25%.

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ACCA Manuals RS,J,S,D,T & B, Air Conditioning Contractors of America. Washington, DC.

ASHRAE RP-1485, Thermodynamic Properties of Real Moist Air, Dry Air, Steam, Water, and Ice. The American Society of Heating Refrigerating and Air Conditioning Engineers.

ASHRAE Handbook 2009 Fundamentals, Chapter 32, “Duct Design" formulas 19, 20, 22, 23 through 28 and Table 1. Chapter 6, “Psychrometrics" equations 5, 6, 12, 23, 25, 28, 31, 32, 34, through 38. The American Society of Heating Refrigerating and Air Conditioning Engineers.

ASHRAE Handbook 2008 Systems and Equipment, Chapter 21, “Air-Cooling and Dehumidifying Coils" equations 37, 38, 39(b) and 40. Chapter 44, “Air-to-Air Energy Recovery" equations 5 and 6. The American Society of Heating Refrigerating and Air Conditioning Engineers.

ASHRAE Toolkit for HVAC System Energy Calculations

Buck Research Manual (1996); updated equation from Buck, A. L., New equations for computing vapor pressure and enhancement factor, J. Appl. Meteorol., 20, 1527-1532, 1981

Thermophysical and transport properties of humid air at temperature range between 0 and 100C P.T. Tsilingiris

Ellipse Equation: Ramanujan, S. "Modular Equations and Approximations to π." Quart. J. Pure. Appl. Math. 45, 350-372, 1913-1914.

Do you have any questions or suggestions? Let Me Know!