Jerry slammed his notebook onto the counter and exclaimed “I will not be your electrician if you don’t put in proper make-up air for your kitchen exhaust system. I will not stand for clients and contractors who cheat the system and end up sick or dead!” The booming voice that emanated from Jerry’s 6’2” frame was enough to finally awaken my clients to what I had been telling them all along – you need to replace the air you take out of your home by bringing fresh air into your home. Failing to do so could lead to toxic air and “back drafting”. This dangerous situation occurs when the toxic by-products of fossil-fuel combustion enter the home instead of leaving it. If your furnace, boiler, water heater, clothes dryer, stove, or fireplace uses natural gas, propane, wood, or pellets you could be at risk. Cheating the system to save a few bucks could leave you with headaches, dizziness, heart pain, or death.
Jerry provided a great visual that I have used with every client since that booming day. Imagine a basketball. It holds “roughly” 1 cubic feet of air (really, it holds much less but a basketball provides an easy visual). If you have a kitchen exhaust system rated “150 cfm” (or 150 cubic feet per minute), you are removing roughly 150 basketballs of air every minute. A 300 cfm system removes roughly 300 basketballs of air every minute. A 900 cfm system removing roughly 900 basketballs of air every minute (the kind typical paired with a “professional-style” range) will remove all the air from an average-sized kitchen within a minute or two. When the air is gone from the kitchen, the exhaust system will pull air from the rest of the house. It can even pull toxic carbon monoxide down flues and vents and pull fire from a fireplace.
To maximize health and safety when installing a kitchen exhaust system, be sure to consider make-up air. Building codes typically require make-up air when exhaust systems are rated at 300 cfm and above. If you live in a super-insulated, air-tight new or remodeled home, you may need make-up air for kitchen exhaust systems less than 300 cfm. Building codes may also require that make-up air be warmed before being brought into living space. Always check the building code of your city.
Be sure the size of the exhaust system is appropriately sized for the heat produced by the cooking surface. This is important to keep the internal parts of the exhaust system from failing. If you install an exhaust system that is too small to remove the heat produced by the cooking surface any damage caused to the exhaust system may not be covered by the manufacturer’s warranty. Always check the manufacturer’s warranty.
Make sure all exhaust systems are vented to the outside of the home. The process of cooking creates moisture – moisture you want out of your home to prevent mold. Recirculating range hoods (those that are not vented outside but force the air through a filter then back into the kitchen) may filter some grease but otherwise send all the moisture-laden air back into the kitchen. Exhaust systems that end in an attic are nothing but a disaster waiting to happen.
Remember, while beauty is important, it isn’t everything. Start with beauty but stir in the right ingredients – a properly sized kitchen exhaust system that is vented to the outside and paired with a make-up air system – to promote safety and to protect your health and your investment.