The equivalent diameter is the diameter of a circular duct or pipe that gives the same pressure loss as an equivalent rectangular duct or pipe.. The table below can be used to compare equivalent diameters for rectangular and round circular ducts. The table is based on the ducts friction loss formula.. The rectangular dimensions and the air flow volume …PRODUCT DETAILS. AIR DUCT SLIDE RULE CALCULATOR. Size: 4"x9.25". Material: Heavyweight coated calculator board. Production: Each order is custom manufactured with your company information and in your choice of colors. AIR DUCT WIZARD DUCTULATORS. Size: 8.5"x11" card with a 7.25" wheel. Materials: Heavyweight coated …Lindab Vent Tools app streamlines ventilation system calculations with practical tools for HVAC professionals. This handy app offers a collection of practical calculation tools for the HVAC industry, including duct dimensioning, pressure drop, airflow, and offset calculation for Lindab's products. The app also includes a k-factor calculator for versatile use …The Duct Size Calculator is a quick reference tool for approximating duct size and equivalent sizes of sheet-metal duct and flexible duct. A new duct-sizing calculator from ASHRAE and the Air Distribution Institute (ADI) allows HVAC air-distribution-system designers to size ducts more accurately, especially flex ducts under …A duct calculator is a tool used to determine the correct size of ducts in an HVAC system. How do I use a duct calculator? You’ll need to know the air volume flow rate, the velocity …To calculate the kinematic viscosity of air at pressure 1 bar (105 Pa) and 50 °C, enter a few details into the kinematic viscosity of air calculator: Convert the temperature in Celsius to kelvin: T = 273.15 K + 50 = 323.15 K. Calculate the density of the air from the ideal gas law: ρ = P/ (RT) = 105 Pa/ (287.05 J/kg·K × 323.15 K) = 1.078 kg/m3.The 922 velocity and air flow calculations are based on standard air at 29.92" hg at 70 °F. Tips. When we talk about positioning the pitot tube 10 straight duct diameters upstream and 3 straight duct diameters downstream of the tranverse plane, we need to first convert rectangular duct measurements into their equivalent circular diameters.Here’s some insight from this chart: To produce 1 CFM, we would need 11.46 FPM, 5.09 FPM, 2.86 FPM, and 1.83 FPM air velocity in 4-inch, 6-inch, 8-inch, and 10-inch round duct, respectively.We can clearly see that we need lower FPM per CFM the larger the duct we use. For 100 CFM, we need between 183.35 FPM and 1145.92 FPM, if we use 4-10 inch …Calculation of duct insulation. Easy program which, by entering a few values, immediately calculates the surface area of the ducts and insulation of the aeraulic circuit under consideration. Valid for quadrangular and circular ducts. In addition to the thickness of the insulation, it is possible to enter waste values (percentage of materials ...Mar 4, 2023 · Duct Sizing Calculator. The duct sizing calculation involves determining the proper ductwork size needed for an HVAC system. The formula used in this calculation is Q=VA, where Q is the airflow rate, V is the air velocity, and A is the area of the duct. V = 0.408 Q/D 2. Components. = Air velocity inside the duct (feet/s) = Air flow rate inside the duct (GPM) = Air flow rate inside the duct (inches) Metric Equation. Determine the following formula, which can be used to calculate the air duct velocity: V …Download HVAC Duct Quantities, Weight and Area Calculation Sheets. Air Duct quantity can be estimated in sq. meters or kilograms. These excel sheets will enable you to calculate or estimate the duct weight or the duct surface area.Instructions. (Input information may generally be be obtained from design documents or field measurements) Line 1. Enter the temperature of the air entering the duct. Line 2. Enter the ambient temperature (the average temperature of the air surrounding the duct) Line 3. Enter the flow rate of the air carried by the duct in cubic …Air Duct Calculator -Slide Rule Style. This rectangular air duct calculator is the technicians favorite. Provides the following information with one setting:- Friction- Velocity- Round Duct Size- Surface Area...and more. Size: 4" x 8.5". ISBN No. 9781622709823Sturdy construction of heavyweight calculator board with 6 metal eyelets.Best prices guaranteed. We match other Aussie retailers*. Use our sizing calculator below to determine the minimum size required for your room or house. Remember for ducted systems only include the air conditioned spaces, exclude areas like …The 922 velocity and air flow calculations are based on standard air at 29.92" hg at 70 °F. Tips. When we talk about positioning the pitot tube 10 straight duct diameters upstream and 3 straight duct diameters downstream of the tranverse plane, we need to first convert rectangular duct measurements into their equivalent circular diameters.An HVAC duct calculator or ductulator is a tool that can be used to calculate the ideal size of your HVAC ducts. It factors in the area size and temperature, air flow velocity, friction loss, and static pressure of the HVAC system.A simple volume unit converter to convert air flow volumes from ... Calculate the equivalent size of spiral ducting when you have only been given the rectangular duct dimension (it works the other way also) Open the ES Calculator. System Pressure Calculator. The System Pressure Calculator helps you work out the resistance in pascals that ... Duct Size Calculator. Ductulator is an engineering tool to calculate air duct dimensions based on given inputs including air-flow, duct material roughness and either air pressure static loss (friction method) or air velocity (velocity method). This online ductulator calculates the dimensions for both round and rectangular duct options (one ... The chart below can be used to estimate velocities in air ducts. The default values are for air flow 400 cfm (680 m3 /h) , duct size 8 in (200 mm) and velocity 1150 fpm (5.8 m/s) . Download and print Air Ducts - Velocity …Air Ducts - Cross Sectional Areas; Example - Generated Noise in Duct by Air Flow. The cross section area of a 200 mm duct can be calculated as. A = π ((0.2 m) / 2) 2) = 0.0314 m 2 The noise generated in the duct with an air flow velocity 10 m/s can be calculated as. L N = 10 + 50 log (10 m/s) + 10 log (0.0314 m 2) = 45 db The noise generated in the same … For 1000 CFM, we need 1650.12 FPM to 11,459.16 FPM, if we use 4-10 inch round ducts. This is quite an enormous air velocity (11,459.16 FPM is equal to 130 miles per hour (mph)). Now, let’s have a look at the 2nd part for rectangular air ducts, starting with the 2nd calculator: The equivalent diameter is the diameter of a circular duct or pipe that gives the same pressure loss as an equivalent rectangular duct or pipe.. The table below can be used to compare equivalent diameters for rectangular and round circular ducts. The table is based on the ducts friction loss formula.. The rectangular dimensions and the air flow volume …Apr 6, 2024 · The Duct Size Calculator is a quick reference tool for approximating duct size and equivalent sizes of sheet-metal duct and flexible duct. A new duct-sizing calculator from ASHRAE and the Air Distribution Institute (ADI) allows HVAC air-distribution-system designers to size ducts more accurately, especially flex ducts under varying amounts of ... AllDuctCalc™ - HVAC Air Duct Calculator v2 Updated 10/26/15: Provide inputs in the blue boxes, other inputs optional. Duct-U-Lator. This app works as a Ductulator and Pressure Loss (friction) calculator which has the following functions. Converts Duct Shape or Size to Another. Determines Sizes for a Given Friction Rate. Determines Sizes for a Given Velocity. Determines Sizes for a Given Velocity and a Friction Loss Rate (simultaneous output) Air Duct Calculator -Slide Rule Style. This rectangular air duct calculator is the technicians favorite. Provides the following information with one setting:- Friction- Velocity- Round Duct Size- Surface Area...and more. Size: 4" x 8.5". ISBN No. 9781622709823Sturdy construction of heavyweight calculator board with 6 metal eyelets.Lindab Vent Tools app streamlines ventilation system calculations with practical tools for HVAC professionals. This handy app offers a collection of practical calculation tools for the HVAC industry, including duct dimensioning, pressure drop, airflow, and offset calculation for Lindab's products. The app also includes a k-factor calculator for versatile use …Best prices guaranteed. We match other Aussie retailers*. Use our sizing calculator below to determine the minimum size required for your room or house. Remember for ducted systems only include the air conditioned spaces, exclude areas like …The Duct Size Calculator is a quick reference tool for approximating duct size and equivalent sizes of sheet-metal duct and flexible duct. A new duct-sizing calculator from ASHRAE and the Air Distribution Institute (ADI) allows HVAC air-distribution-system designers to size ducts more accurately, especially flex ducts under … Ducting Calculators and Air Volume Converter. Nordfab can offer technical assistance with determining whether our ducting is best for your application and with designing duct installations. Please contact us with your requirements. Input CFM Input Velocity (FPM) Ideal Round Duct Diameter Duct Friction in Straight Duct. Calculate. Using the chart, you’ll see that for a 12” round flex duct, maximum CFM is 480 CFM or 500 CFM depending on the friction rate. Duct size for 115 CFM. Find the CFM closest to 115 in the table above. It will be found in different columns depending on the friction rate. If there isn’t an exact match, go up to the duct size. Ductulator - Hand held rotating calculator used for sizing supply and return duct systems using the equal friction design method. Includes scales for friction loss per unit length, air volume, air velocity, round duct diameter, and rectangular duct diameters. One side uses English units, the other side uses Metric units. The two most common insulated rigid ducts are supply air ducts and return air ducts used for air conditioning. Meanwhile, the fresh air ducts and exhaust air ducts in toilets and mechanical rooms can be uninsulated rigid ducts. In HVAC, main ducts and branch ducts are usually rigid ducts. They are more likely in a rectangular shape rather than ...The Duct Pressure Loss Calculator is an essential tool used to estimate the pressure drop or loss that occurs within a duct system due to various factors such as friction, length, diameter, velocity of airflow, and gravity. Its primary function is to calculate the pressure loss (ΔP) occurring in the duct, offering insights into the system’s efficiency.By knowing how to calculate static pressure in air duct systems, you can determine that the right push of air counteracts the resistance in airflow. In a static pressure calculation, we are looking for the push of air to exceed the resistance. Otherwise, the system won't be able to circulate air throughout the ducts.Jul 22, 2022 · Step 1: CFM – System Size & Blower Size. Sizing an HVAC System. Step 2: Maximum Friction Rate. Friction Rate and Ductwork Length. What is TEL? Step 3: Maximum Velocity. Summary of Ductwork Sizing Factors. Our Recommendation. The Pick HVAC Ductwork Calculator. Calculation Method. Static Pressure Loss [inW/100ft] Air Flow [CFM] 3000 FPM. Round Duct Air Velocity. Infinity FPM. Rectangular Duct Air Velocity. 0.00049 Absolute Roughness [Foot] 14.42. Adjustable Absolute Duct Roughness. If selected, Flexible roughness is 0.003 ft when. straight and fully stretched tight at 0% compression. (adjusted at other compressions), otherwise the. original method of constant 0.01 ft roughness is used. Use ASH RAE 2013 Flex Compression. A 4 feet air duct with diameter 2 inch and air flow volume 156 cfm has a friction loss of. = (0.109136 * 156 1.9 ) / (2 5.02) = 1.97603 inches. = (0.109136 * 156 1.9 ) / (2 5.02 )* (4/100) = 49.40069 inches / 100 feet. Air Ducts are passages for air to travel within your home. The loss in pressure of the flow that occurs due to the air ...JP Lamborn Co. ( JPL ) began producing flexible air ducts in 1961. Today the company operates four state-of-the-art manufacturing facilities and is the largest family-owned flexible air duct manufacturer in North America. JPL’s core values of manufacturing high-quality products, providing excellent service, innovation, and strong business ...V = 0.408 Q/D 2. Components. = Air velocity inside the duct (feet/s) = Air flow rate inside the duct (GPM) = Air flow rate inside the duct (inches) Metric Equation. Determine the following formula, which can be used to calculate the air duct velocity: V …Duct calculator. Air and liquid duct; Calculate duct flow resistance, environmental heat exchange, and adiabatic; Note: outer coefficient of heat transfer usually is 3~10, >10 when winds. Download & Buy. For windows, without network and browser limits.Best prices guaranteed. We match other Aussie retailers*. Use our sizing calculator below to determine the minimum size required for your room or house. Remember for ducted systems only include the air conditioned spaces, exclude areas like …Online Head Loss Calculator. The calculator below, which is based on eq. (2) , can be used to calculate the head loss in a duct, pipe or tube.The default values used in the calculator are for air flow 20 o C , 1.2 kg/m 3 and 6 m/s .The default density of water commonly used as reference fluid is 1000 kg/m 3.The friction coefficient is calculated …Knowledge is power, so although we can't always correct the problems we see with duct work, I'm hoping that with some knowledge we can make some little chang...mdot = Q / (cp x Δt) Calculate air mass flow rate from cooling load.To calculate the kinematic viscosity of air at pressure 1 bar (105 Pa) and 50 °C, enter a few details into the kinematic viscosity of air calculator: Convert the temperature in Celsius to kelvin: T = 273.15 K + 50 = 323.15 K. Calculate the density of the air from the ideal gas law: ρ = P/ (RT) = 105 Pa/ (287.05 J/kg·K × 323.15 K) = 1.078 kg/m3.Knowledge is power, so although we can't always correct the problems we see with duct work, I'm hoping that with some knowledge we can make some little chang...The equivalent diameter is the diameter of a circular duct or pipe that gives the same pressure loss as an equivalent rectangular duct or pipe.. The table below can be used to compare equivalent diameters for rectangular and round circular ducts. The table is based on the ducts friction loss formula.. The rectangular dimensions and the air flow volume …Undersized return air ducts result in the ducts and grills being more noisy than usual and the air conditioner components becoming stressed, thus reducing the lifetime of the unit. Use our handy return air duct size calculator or charts below to help you determine the correct return air vent size for your home.The friction loss in a 20 inches duct with air flow 4000 cfm can be estimated to approximately 0.23 inches water per 100 feet duct as shown in the diagram above. The air velocity can be estimated to approximately 1850 feet per minute. A major friction loss diagram for air ducts - Imperial units ranging <i>10 - 100 000 cfm</i>.Section 5 - Air Distribution System Design This section provides an executive overview of duct system design procedures, additionally covering the use of a branch take off fitting at the end of a supply air trunk duct. Section 6 - Duct Sizing Calculations This section covers the duct system design procedures in detail.Duct Sizing Calculator. The duct sizing calculation involves determining the proper ductwork size needed for an HVAC system. The formula used in this calculation is Q=VA, where Q is the airflow rate, V is the air velocity, and A is the area of the duct.Jan 14, 2012 · The Duct Sizing Calculator is a hand held sliding calculator used for sizing supply and return duct systems using the equal friction, or velocity reduction design method. Front of calculator includes scales for friction, velocity, round duct size, weight per linear foot of round duct, surface area in square feet per lineal foot of round duct ... The Digitized Ductulator is a free online calculator for sizing HVAC ducts. Use it in one of two ways; either enter the duct size to find the equivalent CFM, or input the CFM to find the right size of rectangular, round or flex duct. Click here to use the Ductulator. Use the right size duct. Duct that's too big, or too small can cause problems ...October 9, 2023 by GEGCalculators. The size of a return air duct should generally be based on the HVAC system’s capacity. A common rule of thumb is to aim for approximately 400-450 CFM (cubic feet per minute) of airflow per ton of HVAC capacity. For example, a 2-ton system might require a return duct with a size of around 16 inches in diameter.ADI DUCTULATOR. Based on research conducted by Texas Tech University as well as Tennessee Tech University, to study the efect of compression in flexible duct on air flow efficiency, ADI created the Ductulator. This Duct Size Calculator's data is based on flexible duct laying in a straight line on a level surface,and nearly fully stretched (4% ... Duct Calculator EliteTM is an industry leading tool designed to simplify the job of duct sizing for HVAC professionals. This app allows users to calculate duct size, velocity, pressure drop, and flow rate for ductwork . Duct Calculator EliteTM features a highly intuitive interface which allows users to easily enter values with precision ... Air Duct Calculators (Ductulator) 2/5. Watch on. This handy little device allows you to size your new air duct, and better understand what to expect from existing duct work. A Ductulator helps you properly size your ducts, estimate air loss, find the round or rectangular duct equivalent, and determine velocity. It can prevent some costly errors ... Duct thickness. Refers to the thickness of the goods on the actual duct. Duct density. Refers to the density of the material from which the duct is made. Duct weight. Refers to the weight of the current duct per meter. Media density. Refers to the density of the medium flowing through the actual duct. Set to air in the initial position. Media ...AllDuctCalc™ - HVAC Air Duct Calculator v2 Updated 10/26/15: Provide inputs in the blue boxes, other inputs optional.Duct Calculator Elite https://apps.apple.com/us/app/duct-calculator-elite/id665701601These calculators estimate the temperature drop (or rise) of air flowing in a duct or fluid flowing in a pipe. An example is the use of insulation to minimize temperature change (either temperature drop or rise) of a process fluid from one location to another(e.g. a hot fluid flowing down a pipe). Temperature Drop Calculator for Air DuctsJul 22, 2022 · Step 1: CFM – System Size & Blower Size. Sizing an HVAC System. Step 2: Maximum Friction Rate. Friction Rate and Ductwork Length. What is TEL? Step 3: Maximum Velocity. Summary of Ductwork Sizing Factors. Our Recommendation. The Pick HVAC Ductwork Calculator. About Press Copyright Contact us Creators Advertise Developers Terms Privacy Policy & Safety How YouTube works Test new features NFL Sunday Ticket Press Copyright ...ρ = 999.7 kg/m³. Find the dynamic viscosity: µ = 0.001308 kg/ (m · s) Compute the product of the density of water, the velocity of the flow, and L: ρ × u × L = 249.925 (m · s)/kg. Divide the result by the dynamic viscosity to find the Reynolds number: ReD = 249.925/0.001308 = 191,074 The flow is likely turbulent.Dec 3, 2023 · The Duct Pressure Loss Calculator is an essential tool used to estimate the pressure drop or loss that occurs within a duct system due to various factors such as friction, length, diameter, velocity of airflow, and gravity. Its primary function is to calculate the pressure loss (ΔP) occurring in the duct, offering insights into the system’s ... QUICK-GUIDE. Select the duct material from the drop-down list (most duct sizing tools are typically based on galvanised steel ducting by default) Enter the air flowrate in litres/second (can change to cubic metres/second by …This calculator allows for calculating the mixed air temperature of a third air source. An example of a third air stream is a Bypass air duct that goes from the supply air plenum back to the return air plenum. Trane has an excellent Engineers Newsletter describing Dehumidify with Constant-Volume Systems.The Digitized Ductulator is a free online calculator for sizing HVAC ducts. Use it in one of two ways; either enter the duct size to find the equivalent CFM, or input the CFM to find the right size of rectangular, round or flex duct. Click here to use the Ductulator. Use the right size duct. Duct that's too big, or too small can cause problems ... Adjustable Absolute Duct Roughness. If selected, Flexible roughness is 0.003 ft when. straight and fully stretched tight at 0% compression. (adjusted at other compressions), otherwise the. original method of constant 0.01 ft roughness is used. Use ASH RAE 2013 Flex Compression. Here’s some insight from this chart: To produce 1 CFM, we would need 11.46 FPM, 5.09 FPM, 2.86 FPM, and 1.83 FPM air velocity in 4-inch, 6-inch, 8-inch, and 10-inch round duct, respectively.We can clearly see that we need lower FPM per CFM the larger the duct we use. For 100 CFM, we need between 183.35 FPM and 1145.92 FPM, if we use 4-10 inch …Duct Calculator Elite TM is an industry leading tool designed to simplify the job of duct sizing for HVAC professionals. This app allows users to calculate duct size, velocity, pressure drop, and flow rate for ductwork . Duct Calculator Elite TM features a highly intuitive interface which allows users to easily enter values with precision (without the …Now, to properly calculate the return grille size, we have to make these two assumptions: Face velocity is 500 FPM (feet per minute). This is the speed at which the return grille sucks the air from your house into your ducts. Free grille area is 70%. As we know, the grille is always bigger than the duct through which the airflow flows.1. Diameter converter, which converts circular diameters to equivalent rectangular ducts. 2. Ventilation parameter calculator allows the diameter, air speed, airflow and dynamic pressure of your installation to be calculated. 3. Pressure drop calculation tool for installations with straight sections and duct system elements. 4.Apr 6, 2024 · The Duct Size Calculator is a quick reference tool for approximating duct size and equivalent sizes of sheet-metal duct and flexible duct. A new duct-sizing calculator from ASHRAE and the Air Distribution Institute (ADI) allows HVAC air-distribution-system designers to size ducts more accurately, especially flex ducts under varying amounts of ... Air Duct Calculators (Ductulator) 2/5. Watch on. This handy little device allows you to size your new air duct, and better understand what to expect from existing duct work. A Ductulator helps you properly size your ducts, estimate air loss, find the round or rectangular duct equivalent, and determine velocity. It can prevent some costly errors ...Return air duct size for 1-5 ton ACs is 14” to 22” for round ducts and 13”x12” to 32”x12” for rectangular ducts. Use the return air duct size calculator below for accurate dimensions required for your air conditioner or heat pump. There is also a table of return air duct sizes for round and rectangular ducts for ACs from 1.5 to 5 tons. Free HVAC Duct Sizing - in SI/Metric or US/Imperial units. Welcome to CalcuDUCT - the quick and easy way to size ducts for any HVAC application. Download duct static pressure calculator excel sheet XLS. Free spreadsheet program for air duct friction loss calculation. Download Free MEP Calculation Excel Sheets, AutoCAD Drawings, and Training Courses for HVAC, Firefighting, Plumbing and Electrical Systems Design.2. Calculator of different ventilation parameters, with which will be able to obtain the diameter, the air speed, the airflow and the dynamic pressure of your installation. 3. Pressure drop calculation tool for installations with …Duct CFM @ .08 supply .05 return. This calculator does not replace good ACCA manual D or SMACNA principles. It does however provide basic duct sizes and CFMs based on these principles. This calculator can be used to estimate CFM or duct size using round Metal or Flexible "properly installed" typical duct runs.Calculation of duct insulation. Easy program which, by entering a few values, immediately calculates the surface area of the ducts and insulation of the aeraulic circuit under consideration. Valid for quadrangular and circular ducts. In addition to the thickness of the insulation, it is possible to enter waste values (percentage of materials ...Online Head Loss Calculator. The calculator below, which is based on eq. (2) , can be used to calculate the head loss in a duct, pipe or tube.The default values used in the calculator are for air flow 20 o C , 1.2 kg/m 3 and 6 m/s .The default density of water commonly used as reference fluid is 1000 kg/m 3.The friction coefficient is calculated …The head loss calculator below is based on formula (1) : Air Volume Flow - q - (cfm) Equivalent duct diameter - d e - (inches) Duct Length - (feet) Equivalent Diameter - … Rectangular sheet metal duct = .07" on most metal duct calculators. 2900. 40x12. 100 31/2 x14 2200 38x10 220 31/2 x30 2350 40x10. Rectangular sheet metal duct = .07" on most metal duct calculators. 3050. 42x12.
This article provides information on how to use the Ductwork Calculator for air flow CFM, friction loss and velocity. It explains the process of duct sizing diameter with accurate results when the right information is plugged into it. The article also gives a detailed explanation of each step in the process and what data … See more. Pirate shi
Air Duct Calculators (Ductulator) 2/5. Watch on. This handy little device allows you to size your new air duct, and better understand what to expect from existing duct work. A Ductulator helps you properly size your ducts, estimate air loss, find the round or rectangular duct equivalent, and determine velocity. It can prevent some costly errors ...AllDuctCalc™ - HVAC Air Duct Calculator v2 Updated 10/26/15: Provide inputs in the blue boxes, other inputs optional. Formula. The formula for air duct sizing involves the calculation of air velocity (V) and duct cross-sectional area (A) to determine the air volume flow rate (Q), expressed in cubic feet per minute (CFM). Q = A × V. This equation comes from the principle of continuity in fluid mechanics which states that for incompressible flow, the product of ... Air Duct Calculator. Double-sided. Side 1 = standard ducloator with calculations for both round and rectangular duct. Side 2 = Continental vs competitive cross reference for some common GRDs and a Grille sizing chart. Qty 25/package. Example - Calculate Reynolds Number. A Newtonian fluid with a dynamic or absolute viscosity of 0.38 Ns/m 2 and a specific gravity of 0.91 flows through a 25 mm diameter pipe with a velocity of 2.6 m/s .. Density can be calculated from the specific gravity of the fluid and the density of the specific gravity reference water 1000 kg/m 3 - as. ρ = 0.91 (1000 …So, the duct design work is made simpler and easy. Since this is a web-based program, users can log in from any browser using an ID and password. Apart from duct designing, this software also helps in Duct sizing. With DuctQuote, you can. Calculate air flow for duct design; Draws 3D systems; Generate custom quotes using logo and …2. Calculator of different ventilation parameters, with which will be able to obtain the diameter, the air speed, the airflow and the dynamic pressure of your installation. 3. Pressure drop calculation tool for installations with …Duct type: Metal Ductboard Flex Size by: Friction rate Velocity Friction Rate: per 100 ft. in/wg Duct TEL : ft. * include fittings in the Duct TEL Enter either: CFM: or Duct Size: …These calculations are divided in four areas: 1. Diameter converter, which allows converting circular to equivalent rectangular ducts. 2. Calculator of different ventilation parameters, with which will be able to obtain the diameter, the air speed, the airflow and the dynamic pressure of your installation. 3.Air duct cleaning redefines home health. Eliminating dirt, dust and microbial growth from your ductwork can improve indoor air quality while maintaining a cleaner home and increasing HVAC efficiency. Clean ducts mean less dirt in your home and air because ductwork is often the source and pathway for dust and biological contaminants.Now, to properly calculate the return grille size, we have to make these two assumptions: Face velocity is 500 FPM (feet per minute). This is the speed at which the return grille sucks the air from your house into your ducts. Free grille area is 70%. As we know, the grille is always bigger than the duct through which the airflow flows..