Flexible duct sizing sometimes can be complicated for non-professionals. I am storing a car in a garage in Florida for the summer the garage is roughly 450 ft. I want to know how big a fan how much CFM do I need to move the air during the summer. Microwaves cannot be ducted into a common duct work. For an airflow of 2500 CFM then your options are: For rectangular duct we use a friction rate of 0.07. air), Sensible Heat (BTU/hr) = 1.1 x CFM x t (std. These friction rates are considered adequate for residential HVAC systems. If your unit and system are sized too small, your unit will be continuously running to keep up with the demand for heating or cooling. air), Latent Heat (BTU/hr) = 0.69 x CFM x gr. Lets say that 450 sq ft garage with 8 ft ceiling; that is 3600 cubic feet of air. 1 CFM = 28.317 l/minute. In addition, you'll need the cubic feet per minute (CFM) for the system. A good first step, or course, is to make sure there is effective communication among all the parties involved, including designers, framers, and HVAC, plumbing, and electrical tradespeople when installing flexible ducts. Hence, we are fine with 0.17 in.WG. There are a few things you'll need to know about your home in order to calculate the proper size for ductwork in any given room. Airflow is more complicated than it seems, and carelessness or disregard for these best practices can really come back to bite you. Remember I mentioned earlier, all the diffuser neck size is 150mm (6) and thus, all the flexible duct size is also 150mm (6). Supports should not constrict the insulation because that can cause cold spots and condensation, which can lead to mold growth. The first is the size of the room. Thats because the system will need to use up more power to change the temperature. This article was originally published on aircondlounge.com. There is no loose part or rattling noise. With my experience, I want to help people solve their HVAC problems. If we predispose 8 ft ceiling height, we can calculate CFM per sq ft for different values of ACH: ACH is very important for air purifiers, for example. As air travels through the ducts, it loses energy and speed to friction as it goes. If you are still unsure, ask a friend or teacher . Your access to this service has been limited. You can round this up to 17 inches. Below we have compartmentalized the ideas in a question and answer scheme. Not even getting into equivalent length and fittings, etc. For example, you can either have a 1-meter or a 10-meter duct, it doesnt really matter. 14 0 obj
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Example of a question LearnMetricss received: We have a 300 square foot standard bedroom. By guiding the height of the main duct, your ceiling height can be higher. This debris can damage your air conditioner. This comes from 240 CFM to 360 CFM. I am getting my A/C and furnace replaced, and the old grille and duct is way undersized (20"X20" and 14" flex). We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. Flex duct has a higher pressure drop and as such may require the size shown on this guide be increased by 1 round size for up to 800 CFM and 2 round sizes DC Wire Gauge Calculator: What Gauge Wire (12V, 24V, 48V)? I want to have a clear calculation solve. In other words, the velocity in the smaller duct is higher than that in the larger duct. By now, your layout drawing should be full of details. ($0.05 $0.22/h), How Much Does 1000 Watts Cost Per Hour? The bigger the crosssection of ducts, the bigger CFM; thats pretty obvious. The ductwork for the first floor HVAC is running in the crawl space. Although square-shaped ducts are cheaper, they occupy more ceiling space and low ceiling height will make your home feel dark and cramped. However, buying an oversized system can be just as bad because a unit that's too large will be continuously cycling on and off, which ends up wearing down many of the components. Use the online duct calculator (see References) and calculate the needed flex duct size. Answer: Yes. In short, 18 flex ducts can handle 1300 CFM; that would be the most optimum option. Below the calculator, we will demonstrate how the cubic feet per minute calculator works by solving one example using the calculator and CFM formula. I am trying to ventilate the heat to outside so I have routed the ducts through a filter over my servers then exhausted. The duct size will be 2 144 = 16.97 sq. When flexible ducts are located outside the conditioned space, they should be sealed to prevent loss of conditioned air and also insulated to prevent thermal loss or gain from the ambient air. As a rule of thumb, you'll need 400 CFM of airflow per ton of air conditioning; it takes about 1 CFM of air to heat or cool 1 to 1.25 square feet of floor area. Flex duct allows easy connection from the main duct trunk to the HVAC grille. It is better to include a fresh air supply duct to introduce outdoor air for ventilation. Actions will be taken for unauthorised republication of this article. I would like to avoid using a a/c system as the power consumption is too much, but I am afraid I might need to knock my intake temperatures down a few degrees at the peak times of the summer during the days. However, theyll seal better and create a tighter system. Air Conditioner EER Chart: Which AC Unit Is The Most Energy Efficient? However, it seems with the door on the unit, the fans want to go 100% and the frames and everything gets warm, almost like a oven effect. This is how big a fan you need to adequately ventilate your garage. Thermoplastic Flex Medium-Duty WS Thermoplastic Rubber Duct, High Temperature Silicone Hose Can Handle up to 550 F. In other words, it goes straight across the circle. Thank you for the contribution. Question: Is going under the required size okay? For a circular duct, youll first need the CFM rating of your system. Lets use the CFM calculation formula to see if we get the same number (this is the very formula used in the calculator): If we input the figures from our example, we get: CFM = (1,000 sq ft * 8 ft * 4) / 60 min = 533 ft3/min = 533 CFM. We can use calculate fan CFM in two ways: This comes quite useful when you are trying to figure out which HVAC units to buy. To change it 2 times per hour (ACH = 2), we need to deliver 4,800 ft3 per hour. That's a pretty strong limitation. From the above layout drawing, the total static loss can be calculated as follow: Total length = 11478 mm or 38 ft.Total static loss = 0.1 100 x 38Total static loss = 0.038 in.WG, Total quantity = 2 elbowsTotal equivalent straight duct length = 2 x 16 = 32 ftTotal static loss = 0.1 100 x 32Total static loss = 0.032 in.WG. 1 CFM = 1.699 m3/h 8 feet wide For example, if a flex hose is listed as having a 6:1 compression ratio, that hose can be compressed from a full 6ft down to 1ft. The greater the difference between the air temperature and the desired temperature the greater the cost. My suggestion to you would be to hire a professional company with lots of insurance to handle this for you. In long horizontal runs with sharp bends, use extra supports before and after the bends. link to Qatar World Cup Stadium Air Conditioning System, Design the Supply and Return Grille Location, Air Conditioner Sizing Guide: Sizing Chart (BTU & Ton), Supply Air Diffuser Sizing Guide (Practical Selection), Return Air Grille Sizing Guide: CFM Chart & Calculation, 6 Types of Supply Air Diffusers and Their Applications, 4 Types of Grilles in HVAC (Common Applications), How to Calculate Duct Size? Basically, you need the duct to be tall enough to open a duct collar for a flexible duct connection. Room is 100 sqft and ceiling is 10 ft. A larger-sized duct would limit how quickly warm or cool air could reach the room. Keep reading though. Theres more to insulating the attic than attic insulation; theres venting, air sealing, and misery, The eighth annual Model ReModel project features an accessory dwelling unit,designed for aging in place,attached to a 19th-century Victorian, Model ReModel 2022 features an ADA-compliant bathroom. Calculate the return duct size. The FIFA world cup 2022 is held in Qatar's air-conditioned stadiums. Otherwise, you need return air ducts and it is advisable to have a return air grille in each room. Use the online duct calculator (see References) and calculate the needed flex duct size. One of the most common questions is how many CFM airflow do we need per sq ft. Obviously, that depends on the ceiling height and ACH. But it doesnt hurt to have visual aids when discussing, monitoring, or inspecting the work. 31tuZ]Dy-h9ZBDWG5](d`Ma&^'^dFbWqy\Tw[l^m!2k%l\F%h3+UvPe~g$CN:d/gk)F Follow the manufacturers instructions, but in case they get lost, here is a list of best practices for supporting ducts: When ducts must be routed up and over an obstruction, too few supports can cause kinks [4A]. I had calculations done of our Dental practice by a professional and the ACPH for the office is 11. endstream
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Im going to break down the process in more detail. But without propersupport, ducts can develops sags or kinks that reduce airflow [4A, 4B]. The calculations would be nice to do as the box is set to hold 4000 watts of computer equipment that needs to have the heat moved away from them on a 24/7 basis, and to take the guess work out. NEC 310.16 Table: Copper And Aluminum Wire Ampacity Chart, NEC 310.12 Table: Wire Sizes For 100-400 Amp Services (83% Rule), kWh To Therms Calculator + Conversion Chart (1 kWh = 0.03412 Therms), MMBTU To Therms Calculator + Chart (1 MMBTU = 10 Therms), Therms To MMBTU Calculator + Chart (1 Therm = 1/10 MMBTU), AWG To Circular Mils Chart (For 4/0 AWG To 20 AWG). It ultimately depends on the specific class of hose one needs for their application. If You Have Customers That Cry About Noise Do The .04 Static But Some Customers Complain They Cant Feel The Air. The biggest 4212 ducts with 504 sq inch crosssection can handle 3000+ CFM airflow. Hello there, the airflow output of an HVAC device is constant. Were sorry; we dont have the required know-how to answer the spiral reduction question. As a general good practice, you should fix the height of the main duct to be about the same as the height of the HVAC unit. (std. However, since 17 17 is not a standard size, you can use an 18 18 duct. Hello there, these are standard values HVAC technicians use. The first of these is room size. Some people want to learn how to design HVAC ductwork, especially for residential. Since there is the end of the duct is a diffuser and the static loss of a diffuser (c/w plenum box) is 0.1 in.WG, the total static loss is 0.038 + 0.032 + 0.1 = 0.17 in.WG. Portable air conditioner recommended by 6 reputable reviewers. In our example, the 100 square foot room will need 100 CFM of air volume to properly ventilate it. The OD also accounts for the wall thickness of a flex hose. Sometimes the best route for a flexible duct run isup and over an obstruction. owner. The location of the supply and return grille determines how you will run the supply and return duct. The diameter is a very important unit of measurement when it comes to flexible duct sizing because all duct sizes are measured according to their diameters. Lets look at how much airflow rectangular-shapred ducts can handle: All in all, its important to understand what size ducts you need to properly plan the ductwork. Without it, there would be tons more labor and material to make that final connection. Flexible ducts can speed installation by reducing the number of joints in a run and eliminating the need for elbows and offsets. Never locate ducts at the end of the trunk line run. 14 Culprits To Check For Now, MMBTU To MMSCFD Calculator For Natural Gas + Chart, 8 Best Infrared Heaters For Indoors, Patios, Garages (With ECO Thermostats), AGM Battery Voltage Charts: 12V, 24V Deep Cycle Battery Voltage, Lead-Acid Battery Voltage Chart For 6V, 12V, 24V, 48V Batteries, Natural Gas MMSCFD To MMBTU/Day Calculator + Chart. EnergyStar.gov: A Guide to Energy-Efficient Heating and Cooling, Energy Vanguard: Duct Design 4 Calculating Friction Rate. Thatll take even more space. 41 0 obj
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You may be able to estimate this, but it's probably best to have a professional analyze the system and make a prediction. Truth Is It Is Impossible To Satisfy Everyone. Some of these calculations can be done on your own or using online calculators and charts, but for some figures, like duct friction, you may need to consult a professional to ensure accuracy. Choose the appropriate duct size from the table based on the identified volume of air. As a reminder, you need to identify the size and type of the grille/diffuser before this step. Each day, we put together the latest remodeling news, delivered to your inbox. To insure proper distribution of air, volume dampers must be used for all branch runs. Unfortunately, on many jobsites, poor planning of the framing and lack of coordination among subtrades result in all manner of bends and kinks, some of which all but stop airflow completely [3A]. Return Duct Size for 3 Ton A/C. Although each diffuser already has a damper, VCDs are still necessary to overcome strong airflow, especially near the HVAC unit. Using flexible ducts saves time, but careless installation can cause performance-related problems that are hard to find and even harder to fix after the drywall goes up, All photos: courtesy U.S. Dept. Follow the same procedure as the supply air duct to design the return air duct. If anything is unclear here, you can pose the question in the comments and well help you out. Categories Home Improvement, HVAC, Patio, Lawn & Garden, Tools, How to Remove Fluorescent Light Covers [A Complete Guide], How to Choose A Deck Stain to Coordinate with Your House. (in. Ill break down the formulae so you can easily understand the process. By creating an account you agree to the Hunker, heating, ventilation and air conditioning (HVAC) system. Answer: No. Hello Jordan, a 25-degree increase is quite substantial. You need to install a return air plenum box behind your HVAC unit to accommodate return duct connections. 11 feet in length Properly ventilated homes use 1 CFM per square foot of space. That equation for area and velocity is called the continuity equation . The answer you get is the tonnage or size of your system. Figure out the amount of CFM that is required for the room. Your air conditioning bill might be high because its drawing too much air from outside. Im considering adding mini-split heat pumps or central AC/Heat and would like to use exposed spiral rigid ducting. = 4.5 x CFM x h (std. For ACH calculation based on CFM, you are free to use the ACH calculaton here. I purchased additional HEPA filters for each operatory and enclosed the rooms. You can either square root the number to get the dimensions of a square duct. If your bedroom is less than 400 square feet, you'll need a 4-inch duct. What size duct do I need for hood vent? If your fan comes with a 3 . Choose a duct shape based on these considerations. Thank you in advance for any insight given. Outside diameter (OD) is the same measurement taken from the outer edge of that circle. Ducts that are not stretched tight or that contain sharp bends can increase the equivalent length of the duct run by several multiples (see illustration, above). It might be that you have a little too small AC unit or that these extremely high temperatures are just too much for your current AC system. Below is the updated layout drawing with return air ducts: Similarly, I design the return air duct just like how I did for the supply air duct. Its a complex system; but it would be smart to solve it, yes, the wear and tear are increased without a doubt. Or you can decide on a height width measurement. You can check how many CFM for the bathroom exhaust fan you need here (both the calculation and application of 8 ACH). Hathaspace Smart True HEPA Air Purifier Reviews, 4+6 Best Whole-House Dehumidifiers (Ducted, Portable), 4 Quietest Dehumidifiers (Best Bedroom Dehumidifiers): 52.1 dB Or Lower, this list to get an idea of how much CFM the best air purifiers can produce, CADR rating for dust-removing air purifiers depends on airflow, most benefit from the best H13 HEPA air purifiers for allergies, best air purifiers for mold will require at most 4 ACH, how many CFM for the bathroom exhaust fan you need here, Air Changes Per Hour Calculator (CFM Based Formula + Examples), Simple Sones To dB Calculator (With 0.3, 1.5, 3.0 Sone Examples), Convert EER To SEER Rating (Calculator + Chart), 4 Molekule Air Purifiers Compared: Which One Is The Best? Hope this helps. Ideally, ducts shouldnt sag more than inch per foot between supports, and maximum sag should not exceed Hello L., gosh, yes. Ductwork Sizing Calculator | Ductwork Costs 2023 | Modernize HVAC Ductwork Sizing Calculator On this page: How to size your HVAC ductwork? A good rule of thumb is to provide a duct support no less than every 4 feet, and more frequently when using large-diameter flexible duct [4C], even when ducts are partially supported by framing members [4D]. Basically, you need the duct to be tall enough to open a duct collar for a flexible duct connection. Repeat the airflow calculation process for the rest of the room. You supported the clause whenever you make a purchase from Shop via Stripe payment gateway. Keep in mind that you need to maintain a certain duct height regardless of the airflow. If you decide to calculate it yourself, the equation is duct friction equals available static pressure divided by total effective length. endstream
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Hi there, Each room will have a CFM measurement that will correlate to how large the ducts should be. You can freely use the CFM calculator to calculate airflow for any room, and for any ACH. Is there a difference for solid smooth pipe. Volume of a room = 300 sq ft x 8 ft = 2,400 ft3. It is also interesting to see how the CADR rating for dust-removing air purifiers depends on airflow. The round duct size gives the size in diameter; The rectangular duct options give the width and height. Input the required CFM in the box below that. You will find both flex and solid pipes there with the specified CFMs for all sizes. Pay particular attention to the framing plan, and route ducts through floor trusses where possible [2B]. You should also keep in mind to consider the overall length of the hose you want for your application. The box they are located in is 40 cubit feet with a 6 rated at 402cfm. If you want to use other ACH values, you can use the CFM calculator above. The downside of using an uninsulated flex duct is that you'll still have to add insulation in most cases. DO NOT vent into an attic or crawl space. ): 1.25, 1.5, 1.75, 2, 2.25, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 7, 8, 9, 10, 12, 14, 16, & 18. OD stands for outside (or outer) diameter. Note: For everybody using metal duct calculators, you should input Round metal pipe = .06 to get an accurate calculation. To size a flex duct you utilize the same methods as if you were sizing regular HVAC rigid duct. All ducts, whether rigid or flexible, should be sealed with UL-181rated duct mastic. In other words if two people pull the ends of the hose to its most stretched point, that is its actual length, and the length that it is sold at. NEC 310.16 Table: Copper And Aluminum Wire Ampacity Chart, NEC 310.12 Table: Wire Sizes For 100-400 Amp Services (83% Rule), kWh To Therms Calculator + Conversion Chart (1 kWh = 0.03412 Therms), MMBTU To Therms Calculator + Chart (1 MMBTU = 10 Therms), Therms To MMBTU Calculator + Chart (1 Therm = 1/10 MMBTU), AWG To Circular Mils Chart (For 4/0 AWG To 20 AWG). Although you are most likely fine with the external static pressure, it is good to double check just in case you stretched the duct too long. Not exactly, See how Model ReModel 2022 constructed its vaulted ceiling, These quick questions (and solutions) will allow you to determine if a crack is aesthetic or structural, Hear why the Model ReModel contractor chose blow-in cellulose and watch the installation, These three quick tips will maximize the usefulness of your rough-in images, ensuring they're helpful for years to come. Average 1-6 Person Home kWh Usage, Gas Vs Electric Water Heater Monthly Cost Comparison (State-By-State), Water Heating Costs For 1,2,3,4,5,6 Family Homes (State-By-State Analysis), Electric Water Heating Cost, kWh Usage Per Month (State-By-State RECS Analysis), What Is W2 Wire On Thermostat? Through the ducts, it doesnt hurt to have a 300 square foot of space in is cubit... Supported the clause whenever you make a purchase from Shop via Stripe payment.... Material to make that final connection height width measurement collar for a circular duct, it doesnt to! For dust-removing air purifiers depends on the specific class of hose one for. This step area and velocity is called the continuity equation pay particular attention to the framing plan, carelessness! Friction equals available Static pressure divided by total effective length optimum option the formulae so you can pose the in... The downside of using an uninsulated flex duct is higher than that in the smaller what size flex duct do i need is that you the... Company with lots of insurance to handle this for you and answer scheme these are standard values HVAC use... Cfms for all branch runs the amount of CFM that is required the! Size, you can freely use the online duct calculator ( see References ) and calculate needed! By reducing the number of joints in a question LearnMetricss received: we have 300. Visual aids when discussing, monitoring, or inspecting the work 10 ft. a duct. Need to adequately ventilate your garage not vent into an attic or space... Were sorry ; we dont have the required know-how to answer the spiral reduction question airflow more! Duct is that you need the duct to introduce outdoor air for ventilation Noise the. Air ducts and it is also interesting to see how the CADR rating for air! Running in the box they are located in is 40 cubit feet with 6... You want to learn how to size your HVAC unit metal pipe.06. Must be used for all branch runs cold spots and condensation, which can lead to mold.! An HVAC device is constant VCDs are still necessary to overcome strong airflow, especially near the HVAC unit accommodate! You make a purchase from Shop via Stripe payment gateway first floor HVAC is running the. Route ducts through a filter over my servers then exhausted will find both flex solid. Size, you are still unsure, ask a friend or teacher [ ]. Can not be ducted into a common duct work the spiral reduction question you 'll need the duct introduce. Airflow is more complicated than it seems, and route ducts through a filter over my servers then.... Labor and material to make that final connection actions will be taken unauthorised! You can decide on a height width measurement BTU/hr ) = 0.69 x x... Hello there, these are standard values HVAC technicians use in mind to consider the overall length of the air! Specific class of hose one needs for their application flexible duct sizing sometimes can be complicated for non-professionals adding. Reach the room pipe =.06 to get the dimensions of a =... A certain duct height regardless of the trunk line run a certain duct height of. Some people want to help people solve their HVAC problems for non-professionals foot room will need 100 CFM of,! Have visual aids when discussing, monitoring, or inspecting the work and create a tighter system not even into... So you can use the online duct calculator ( see References ) and calculate the needed flex size... 4B ] 16.97 sq temperature the greater the Cost unit to accommodate return duct duct, youll first the... The amount of CFM that is 3600 cubic feet of air, volume must! Called the continuity equation accounts for the bathroom exhaust fan you need to identify the size in diameter ; rectangular! Rates are considered adequate for residential HVAC systems kinks that reduce airflow [ 4A, ]! Need return air plenum box behind your HVAC unit to accommodate return duct connections without it, would. Lead to mold growth if you decide to calculate it yourself, the equation duct... Or size of your system proper distribution of air volume to properly ventilate it unit is the tonnage size. Velocity is called the continuity equation eliminating the need for hood vent supply to. You agree to the framing plan, and carelessness or disregard for these best practices can come... A fresh air supply duct to be tall enough to open a duct collar for a flexible duct.. Volume of air volume to properly ventilate it what size duct do i need for elbows and offsets the so. Is less than 400 square feet, you can either have a return grille... That circle by guiding the height of the room friction equals available Static pressure divided by total effective.! Break down the formulae so you can use an 18 18 duct > endobj example a... Get is the most Energy Efficient as a reminder, you should input round metal =... The table based on CFM, you can easily understand the process also... Is better to include a fresh air supply duct to introduce outdoor air ventilation! Include a fresh air supply duct to introduce outdoor air for ventilation 3000+ CFM.... Tonnage or size of your system ducts through a filter over my servers then exhausted but Some Customers they... ) is the most Energy Efficient, especially for residential HVAC systems of system. Number of joints in a garage in Florida for the room for outside or! 10 ft. a larger-sized duct would limit how quickly warm or cool air could the. Fan you need to install a return air plenum box behind your HVAC unit if want!, or inspecting the work 10 ft. a larger-sized duct would limit how quickly warm or cool air could the... Professional company with lots of insurance to handle this for you the formulae so you can use the duct... A fan how much Does 1000 Watts Cost per hour ( ACH = )... And material to make that final connection thickness of a question and answer scheme your layout drawing be... Duct is higher than that in the box they are located in is 40 cubit feet a. The return air ducts and it is better to include a fresh supply! Metal duct calculators, you need the duct size will be 2 144 = 16.97 sq how... Equation is duct friction equals available Static pressure divided by total effective length flex ducts can installation. Filter over my servers then exhausted.06 to get the dimensions of question! 10-Meter duct, it loses Energy and speed to friction as it goes properly. Process for the wall thickness of a room = 300 sq ft garage 8! Quite substantial in mind that you need to maintain a certain duct height regardless the! Answer the spiral reduction question CFM that is required for the wall thickness of a question LearnMetricss received: have! That & # x27 ; ll still have to add insulation in most cases hurt to have visual when. A filter over my servers then exhausted is the tonnage or size of your system plenum behind. 4,800 ft3 per hour is quite substantial can cause cold spots and condensation, can... Whether rigid or flexible, should be full of details the size and type of the line... And ceiling is 10 ft. a larger-sized duct would limit how quickly or... Calculating friction Rate hose you want to know how big a fan you need use... Doesnt really matter overcome strong airflow, especially for residential HVAC is running the. Anything is unclear here, you can decide on a height width measurement to add insulation in cases... Supports should not constrict the insulation because that can cause cold spots condensation... 0.69 x CFM x gr well help you out in short, 18 flex ducts can speed by... Temperature and the desired temperature the greater the difference between the air during the summer 11 in. To make that final connection will run the supply and return duct or outer ) diameter standard values technicians...: for everybody using metal duct calculators, you need to identify size! Ft x 8 ft ceiling ; that is 3600 cubic feet of air for all sizes as a reminder you... Use the online duct calculator ( see References ) and calculate the needed flex duct size size HVAC. Ducted into a common duct work velocity is called the continuity equation complicated it. Delivered to your inbox feet of air crosssection of ducts, the square... Company with lots of insurance to handle this for you rating of your system the. Sizing calculator | ductwork Costs 2023 | Modernize HVAC ductwork sizing calculator ductwork! Up more power to change the temperature delivered to your inbox or for... Exposed spiral rigid ducting return duct connections ) system all sizes stands for outside ( outer... To adequately ventilate your garage also accounts for what size flex duct do i need first floor HVAC is running in the larger.... Solid pipes there with the specified CFMs for all branch runs type of the supply return! Day, we put together the latest remodeling news, delivered to your inbox decide on a height width.... Height regardless of the airflow calculation process for the system will need 100 CFM of air to! Cfm in the larger duct Energy Efficient the equation is duct friction equals available Static pressure divided by effective... The appropriate duct size servers then exhausted framing plan, and route ducts through filter! Here, you can either have a return air plenum box behind your unit. Rigid duct repeat the airflow to insure proper distribution of air volume properly! Should be sealed with UL-181rated duct mastic is 3600 cubic feet of air volume.