How to calculate cfm for range hood - all you should know
It is a measure of air flow.It is a measure of the rate at which air is moved.The greater the volume of air that is moved, the higher the CFM.
A residential kitchen range hood calculator can be found on this page.The calculations are based on the recommendations of the HVI.
There is a lot of false information out there.Most of the so-called guides base it on commercial establishment requirements which results in people needing more than what most homeowners will ever need.
There are a lot of "rules-of-thumb" that don't solve the real simple mathematics.Through this calculator, I explained the process and took care of it for you.
I am not going to get into the theory right now, but you can find details and formulae just below the calculator.You can get there by clicking here.
The recommendations are based on the HVI and you are free to make your own decisions.Makeup air is required when you install a range hood with a CFM greater than 400.The output from this calculator is a guideline as to what CFM would be best for you.
The specific instructions given to you at different sections are not the only thing you should keep in mind.If you want to write 20,000, write 20000.When necessary, feel free to use decimal points.If you fill in all the necessary information within a section, you'll get the wrong output.
You can either hit the enter key on your keyboard or use the submit button at the end of the calculator to determine the optimum CFM for your home.
The section is based on the HVI minimum and recommended CFM, as well as the type of range hood installation and the dimensions of the cooking range.The exact guidelines of the HVI institute can be found below the calculator.
You can only enter the dimensions in one of the boxes below.
If you happen to know both, enter BTU or Watts.The output would be based on the larger requirement if you enter a value in both fields.If you want to use all the burners at the same time, you don't need to enter the total wattage.
For example, if you have a stove with four burners, each with a BTU of 10000, but you only use a maximum of two burners at a time, enter your BTU as 20000 and not 40000 because in this case, you do not.The same applies to an electric stove.
All the air in your kitchen needs to be replaced at least 15 times an hour.This happens once every 4 minutes.We need to calculate the volume of your kitchen in order to determine the CFM needed to achieve this.
Depending on the type of duct material you use, the total length, number of turns, and the presence or absence of a roof cap, there will be losses in CFM.The final CFM required to meet your requirements needs to be calculated using this data.
Enter 1 for flexible ducting and 2 for non-flex.The right results would not be given by any other value.
For the purpose of this discussion, the kitchen is that value which is adequate to remove any excess moisture, cooking odors, indoor air pollutants, etc.How well the range hood captures the fumes depends on what is cooking.
Depending on the type of cooking and the position of the cooking range, the amount of ventilation needed varies a lot.When compared to downdraft exhaust systems, which require a higher volume of air for the capture and exhaust of the contaminants, range hoods which are placed above the cooktop capture them with their canopy and effectively exhaust them.The HVI doesn't give recommendations for downdraft range hoods, but they do ask you to consult the range hood manufacturers to figure out what you need.
Range hoods have to be compatible with the exhaust generation rate of your cooking range and the type of food you cook.If you cook food with a lot of emissions, you will need a powerful range hood, above the minimum requirements.The performance of your range hood is dependent on the dimensions of the duct.The range hood won't perform at its rated capacity if it has bad ducting.Depending on the length of the duct and the bends, the range hood's efficiency is lowered.
The Home Ventilation Institute has a list of minimum requirements for kitchen exhaust systems as well as their suggested values per foot of your range.
The requirements for standard range hood dimensions for wall backed cooking ranges and island ranges can be found in the tables below.
These requirements only take into account the dimensions of your cooking range, not the ducting, etc.The recommended values are based on the average cooking requirements.If you think you cook more food with more emissions of vapor, smoke, and grease than the average homeowner, you're going to have to upgrade your range hood to do a better job.
The average kitchen is between 10 feet and 8 feet.You can use the calculator to figure out what you need for your kitchen.This can be difficult for homes with an open kitchen plan.It's best to talk to a local expert.If you can't do it, you should make sure that you have a range hood with a capacity that is larger than the one you need to fulfill the other conditions.
You need to take into account the rate at which it produces heat, as well as the dimensions of the cooktop and its location.British Thermal Units are used to measure the amount of heat produced.
If you look at other websites that talk about Range Hood requirements, you will see that they assume a factor of 100 lower.This is not correct and must be 6.13 CFM.The wrong calculations almost double your requirement.I have a lot of sources and calculations to back up my statement.I don't believe in throwing numbers around with no explanation.Let's do some math together.
To fully understand the calculations, we need to go through some basic definitions and convert everything to the SI system, which is the system used globally for scientific calculations.There are relevant sources for conversions.They are also provided.
We now have a conversion between the two.We would like to convert Watts to CFM.Let's get these relations by moving things around.
47.82 Watts is the amount of one CFM.100 Watts equates to 2.09 CFM.This is similar to what the tables show.
The difference between 1000 and 100 Watts is 2.09 CFM.The number of Watts equals the amount of air.We have reached the conclusion that 1000 BTU is not 10 CFM.It can be expensive to follow general rules of thumb.This is the same as on the calculator.
The size of the room is another factor that needs to be considered along with the cooktop dimensions and heat production.If you don't have other means to refresh the air in your home, this is a good practice.
If you want your range hood to expel all the air from your kitchen, you should be able to do it 15 times an hour.Divide the volume of your kitchen by 4 to calculate the necessary CFM.This is the most important factor when it comes to range hood power.You have to decide if this is something you need or not.It is not necessary for you to be able to open your windows or use other means of exhaust during the day.This article explains why capture efficiency is important.
If your kitchen is 15 feet by 10 feet, you need a CFM of 151510/4.
The general public is not aware of a few points regarding range hood efficiency.When selecting your range hood, please keep these in mind.
We've seen the base CFM that you would need.If you duct a range hood, you're going to need additional CFM to compensate for the losses.The amount of ductwork, the number of bends, and the presence of a roof- cap are some of the factors that affect this.
There is no way to program an online tool to determine the exact losses due to the ducting because of the many different factors that go into it.You can play a role.
There is no need for us to get into the details because there is a simple way to estimate your losses.If you use flexible ducting, there is a 7% loss in CFM for every 25 feet, while metal ducting has a 3% loss.There is an additional 3% loss for every 90-degree bend.If you use a roof cap, there is an additional 3% loss.
You lose 25 CFM on a 90 degree bend, according to most websites.Most of the time, this is way off the mark because it is simplified too much.The websites written by non-tech people who don't seem to bother that they are providing wrong information that costs people would blow up the CFM you require.
The requirements are displayed to you based on the different criteria when you use my calculator.The minimum and recommended capacity are highlighted by a specific output.
You wouldn't pick the maximum CFM based on the values.It is possible to calculate the CFM based on the volume of your kitchen, but later decide that it is not something you would want to stick to.
When determining the losses due to duct efficiency, I do not give you the ultimate losses or the excess CFM because I don't know which one you decide to go by.If you were to buy a range hood with that particular CFM, I will give you a factor that you need to use in order to determine the actual output.
If the CFM is determined to be 400 and you have 12 feet of non-flex ducting with one 90-degree bend and a roof cap, the calculator would do this:
You lose 3% of the capacity for every 25 feet of ducting.You get 100 - 1.44% of the original, which is 98.7% of 400.A total of 394.24 liters of air per minute.You lose 3% due to the bend.Since you lost 3% from 100%, the total loss is 98.7%.This results in a CFM of 382.41, as the output is now 97% of 98.61% or 95.60%.There is a 3% loss due to the roof cap.98% of 95.60 is the total output.It was 92.73% or more.This is a loss of air.
In this case, the calculator's output would be 0.9273.The only thing you have to do is take the number and add it to the CFM you need.To get the result, 400 CFM.
The Engineering Toolbox has a page that can help you determine the precise losses for your installation.The page talks about the perfect duct diameter.Make sure you follow the manufacturer's recommendations and don't modify the duct diameter unless you are aware that this could void your warranty.
Finally, you acknowledge that this calculator is developed to serve as a guide and you are advised to speak to a local expert to determine the exact CFM that you need.I don't have to be responsible for the wrong use of this calculator or if the methods used are faulty.The results are good for use to the best of my knowledge and understanding because of the links and verifications provided.
It's all you would need for most homes.You have to install a system for make up air while you install your range hood if you go above 400 CFM.If it is required by law to install make-up air, they will not care if you use a speed setting above 400 CFM or not, as long as you buy a range hood that does not exceed this power rating or one that can.I suggest you use my free calculator to figure out the exact CFM.
The location of your stove, the output of the stove and for kitchens with absolutely no other exhaust are all factors that need to be taken into account.
The power output of your stove is the most important factor.Most websites suggest that you need 10 CFM for every 1000 BTU, but this is wrong and you only need 6.13 CFM.The difference adds up and makes a difference.It is a double of what you really need.If you want to know more, I have explained the math behind it.
If you don't want to do the math, use my calculator.You need 1 CFM of power for an electric stove.Divide the total kitchen volume by 4 to determine the CFM.
It depends on the location of your stove, the power output of it, and the volume of the kitchen, but it's not always necessary.You can find complete details on how to calculate it yourself and a range hood calculator on this page.
If you are building your own range hood, you would want to make sure that the flow rate is within limits so that you don't have noise or losses.I don't want to reproduce data that the engineering toolbox has done well.The purpose of this page is to determine the CFM and not the ducting.Follow the instructions in the manual for the dimensions of your ducting if you are buying a range hood.
Are you sure if you found the right hood for your kitchen?You may want to check out some of the other choices I've reviewed.