The following article from Pro Trade Craft gives more insight into how your kitchen exhaust should properly ventilate your kitchen and be apart of the mechanical system.
Range hoods need to do more than sit there and look pretty: they are a key player in the mechanical system
Many people do not consider the range hood to be part of a house’s ventilation system, but they are. Monster range hoods that suck large volumes of air out of a house are (by definition) sucking large volumes of air into the house at the same time.
Like it or not, the kitchen exhaust has to play nice with the rest of the mechanical system.
This is especially important in tight houses and energy efficient retrofits.
Today, we’re consolidating that research into a concise hit list for you to execute in the field.
Standards, codes, and high performance ratings
ASHRAE 62.2 is a standard that defines optimal ventilation rates for homes. Building codes and Energy Star use 62.2 to define mandatory ventilation rates for homes. Kitchen fans are part of that equation.
Range hoods typically turn on when a person turns them on and they turn off when a person turns them off. This is called ‘intermittent use’ or ‘occupant operated’ by people who like to make sentences harder to read than they need to be.
Fans can also run continuously.
Continuous exhaust fans must be quiet, or people will unhook them—less than 3 sones is suggested by HVI.
Energy Star goes a little further for continuous-flow kitchen fans: they should have low power and have multiple operating speeds to bump up for spot ventilation.
The range hood duct should have a smooth interior finish (easy to clean), be airtight, and be equipped with a backdraft damper.
How to install a kitchen fan right
Kitchen exhaust fans are often installed by many different trades: remodelers, electricians, range hood vendors … whoever does it should follow these steps:
1/ Choose the right size exhaust fan for the application.
- Kitchen fans operated intermittently should move 100 CFM of air or more. Energy Star recommends selecting a fan with a rating of 150 to 200 CFM to pull at least 100 CFM when measured.
- Continuous fans should move 25 CFM of air. Energy Star recommends fans that will get you at least 5 air changes per hour (ACH) based on the kitchen’s volume.
2/ Install the fan above the stove: either in the range hood, cabinet, or in the wall.
- Cut a hole for the fan or duct slightly larger than needed and air seal the opening with caulk or low-expansion foam after installing fan.
- Don’t use duct tape, use mechanical fasteners, foil tape, mastic, or all three. Duct tape is for wallets.
- Exhaust hoods installed over broiler units should have at least 24 inches clearance above the cook top and the hood should extend the full width and depth of the cooktop.
3/ Vent the fan to the outside: not into the attic.
- Or the crawlspace. Even if it is vented. Period.
- Straight duct is better than flex duct, fewer bends are better.
- Don’t downsize the ducts: small vents can trap grease and cause a fire.
- Seal the seams in the ductwork with the aforementioned metal tape, mastic, or both.
- Don’t dent the ducts. Misshapen ducts really change the way the air flows through the pipe, and not for the better.
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