How To Determine The Right Range Hood For Your Kitchen

Keep in mind range hoods are usually not required by most local building codes, however cooking without them can lead to smoke and smells left in your kitchen. Check with your local county for any codes that would be required before starting your kitchen remodel. Here are a couple of measurements and tips before you start your project.

To properly calculate the amount of CFM’s (cubic feet per minute) for your range hood you’ll need the following:

 Size of your range

Gas ranges you’ll need the total BTU’s (British thermal units)

Size of your kitchen (Width Length & Height)

 Length & angles of ductwork being used

Range Size Calculation:

A basic rule used to determine your range hood would be for the hood to move a minimum of 100 CFM for every 12” of range width.

·         Example a 30” range would be 2.5’ x 100 = 250 minimum CFM range hood

Gas Range BTU Calculation:

Gas ranges produce a lot more heat than electric ranges so gas ranges will require larger CFM requirements. You’ll need to combine each of the range burners to determine the total BTU’s for your range and divide the total by 100 to determine the correct CFM for your range.

·         Example of a 5 burner range (1 x 15,000, 2 x 10,000, 2 x 5,000 = total of 45,000 BTU’s)

·         45,000 ÷ 100 = 450 CFM for the range

Kitchen Size Calculation:

Your kitchen size should also be considered when calculating CFM to help maximizing the correct amount of air flow within your kitchen. Range hoods should be able to exchange the air a minimum of 15 times per hour or once every 4 minutes.

·         Example of a kitchen 16’ wide x 12’ length x 10’ high (16 x 12 x 10 = 1920)

·         1920 cubic foot room x 15 air exchange = 28,800 cubic feet to move per hour

·         28,800 ÷ 60 = 480 CFM for your kitchen

·         Or total cubic feet of 1920 ÷ once every 4 minutes = 480 CFM

Ductwork Calculation:

Every length, turn and cap in your ductwork adds resistance in air flow, there for these things must be noted to determine the correct amount of CFM required for your project.

When using an 8” round ductwork the following additions will be added.

·         Add 1 CFM per foot of pipe length used.

·         Add 25 CFM for every elbow being used.

·         Add 40 CFM for roof caps being used.

·         Example: 10 foot pipe length + 25 elbow + 40 roof cap = 75 CFM

The final calculation is to take the largest CFM rating plus the ductwork to determine the hood for your project.

Example of the above calculation:

Range size (250 CFM) Gas range (450 CFM) Kitchen size (480 CFM) and the added ductwork (75 CFM)

The following CFM would be required. Largest CFM was (480) plus ductwork (75) = total of 555 CFM as the minimum requirements for the project.

We hope that these measurements will help you figure out what you need. After reading this and you feel lost, please give us a call and we can help you with the specs and make sure that you are getting the right hood and appliances for your kitchen. 

Do You Need Makeup Air for Your New Range Hood?

Your lack of makeup air might be the next reason your home does not pass inspection.

A code from 2009 dictates kitchen range hoods with exhaust rates of 400 CFM or greater must have makeup air, or replenishment air, added back into their homes to replace the oxygen exhausted outside.

The need for makeup air has become more and more relevant as newer homes allow less and less air to enter or escape. A 400 CFM hood was not likely to suck out all of the oxygen in an older, drafty home, but in today’s energy efficient, virtually airtight homes, high powered hoods can and are dangerous.

Specifically, makeup air significantly reduces the risk of carbon monoxide poisoning. Without the addition of makeup air, air pressure can eventually drop causing a back draft to occur, which then creates a vacuum that inhibits carbon monoxide (from the gas range, furnace and water heater) from venting outside. Carbon monoxide can then reach unsafe levels that even lead to death.

So yes, you probably need makeup air if you want a powerful range hood.

If adding makeup air is not feasible or too costly, then look into Zephyr’s hoods with Airflow Control Technology (ACT). Exclusive to Zephyr, the feature allows the exhaust rates of their hoods at the time of install to be lowered to 390 CFM, which is safe and to code, and still a powerful ventilation option. The only downside? It can’t be reversed. 

Find the right makeup air by Zephyr on Contract Appliance. Contact us if you have any questions.

What is Make-Up Air and What Does it Have to Do With Buying a Hood?

Make-up air is outside air purposefully brought back into your home to replace the air hoods exhaust outside. Providing for make-up air protects against carbon monoxide poisoning and ensures hoods perform at their best.    

We won’t bore you with too many details, but high-end range hoods with faster exhaust rates inhibit normal air pressure from pulling in clean, outside air through chimneys, window and door seals, and so on. Without make-up air, “backdrafting” occurs which pulls poisonous carbon monoxide back into the home when it should be venting outward. This same phenomenon can occur in a dryer vent and push highly flammable lint into a gas-burning motor, hence why cleaning out your lint trap is so important.

The need for make-up air is stressed even more so in today’s energy efficient homes because they’re practically air-tight. Section M1503.4 of the 2009 International Residential Code notes that you don’t need a make-up air system for range hoods rated at 400 CFM or less.

Implementing a make-up air system is the only “right way” to meet code and protect against carbon monoxide poisoning. The concept shouldn’t be new to any licensed contractor and there are many acceptable methods (like the example below).

However, if the “right way” isn’t an option, Zephyr Hoods introduced a new feature called ACT (Airflow Control Technology), which allows the blower strength to be reduced down to 390 CFM. Many popular hood styles are only available on units with 600 - 1,200 CFM and the ACT feature allows for those styles to be used safely without the need for make-up air. The downside? It’s not available on all models.