Range Hood Makeup Air
Range hood Makeup Air:
Code Requirements & Poisoning
If you're going to get a new ducted range hood, you obviously want to get one with enough of power under the hood. However, when you pass a certain threshold in terms of power, by law you will be obligated to take certain precautions in order to prevent carbon monoxide poisoning, which can happen through something called backdrafting. To prevent this, you might have to provide range hood makeup air. Please read on for your own safety.
The following information is what manufacturers usually won’t explicitly mention in their sales pitch, even though it’s very important. It’s actually so important, the law demands it. However, since the range hood manufacturers want and need to sell as many of their range hoods as possible, some have chosen to withhold this information, as it could mean the difference between buying an expensive model and a cheap(er) one. Not only is this morally questionable to say the least, it's also dangerous or even life-threatening.
Like we've shortly mentioned before, some people immediately want to buy the biggest, baddest commercial grade range hood they can get their hands on and install it in their home kitchen. You might have a big family and therefore need to prepare a lot of big dinners. Others just want to impress their friends. A nice big and shiny range hood in the kitchen can be a great eye catcher, right? 1200 CFM? Make it 1600 CFM! Better to be safe than sorry, right? No. Not only would that be overkill for the average household and would consume large amounts of energy, it would actually be very dangerous to put it in your residential home without the proper precautions, as it will likely create a backdrafting problem. A what problem? Let us explain.
As you know, range hoods suck up air from the kitchen and export it out of the building. As you know, the higher the CFM of the range hood, the faster the air is transported out- side. Obviously, the longer a range hood is turned on, the more air it will transport outside. When that happens, it will create a shortage of air within the kitchen (a negative in-house air pressure), because a large amount of air is being transported out of the kitchen, but nothing is coming in. To balance out the air pressure, new air (called makeup air) will usually come in through random air leaks
throughout the house (called backdrafting). However, due to houses becoming more and more air-tight and well-isolated, the range hood makeup air has to come from other places. In practice, this usually means it comes in through undesirable exhaust routes (e.g. fireplace, furnace, dryer vent, hot water heater), which might cause carbon monoxide and other harmful pollutants to be sucked into the house and cause (carbon monoxide) poisoning.
This guy gets it. Plus, he's wearing a hard hat, which means he knows a lot about building stuff.
According to the International Residential Code (IRC) 2015 (M1503.4), if you want to install a range hood with more than 400 CFM, it’s required to install a makeup air system which can move fresh air back into the kitchen at the same rate as the range hood can transport air out of the kitchen. This air intake system needs to have at least one damper, either a gravity damper or a damper which opens automatically once you turn on your range hood. Not having such a range hood makeup air system means that you’re in violation
of your city's or state’s building code. However, check your own state’s building code, because the CFM threshold to supply makeup air may vary from state to state. (E.g. in the state of Minnesota the threshold is 300 CFM.)
Luckily, some manufacturers have started to design such range hood makeup air systems, so that people will be safe from harm by meeting the range hood code requirements. They usually include a sensor of some type which senses when to open up the damper and let the fresh air in. Example:
FREE Range Hood Buying Guide
Check out our FREE GUIDE to buying a new range hood to check how much CFM your range hood will need. (Includes a downloadable PDF on page 1).
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