It is true that recirculating, or ductless range hoods, don’t require any duct-work, but these are far less efficient than standard ducted hoods for that very reason. In essence, unless you have no other choice, you’re going to want to opt for a typical ducted range hood which also means you have to plan ahead when deciding how the range will ventilate exhaust outward.
The type of material that should be used for your range hood duct- work is steel. Steel will stand up to the heat , and is also smooth making it more difficult for the small grease particles to accumulate inside the duct. This material will also prevent fires, and is less capable of acquiring holes. Flex duct should not be used at all, and could be a violation of code depending on where you live. Check with your local building inspector for the correct duct material in your area.
Ideal ducting length
Assuming all the vents and duct-work are not pre-installed in your home or kitchen, you have a number of choices when deciding on ventilation and there are some things you should keep in mind. For starters, if possible keep the duct length under 30 feet tops. Any longer makes it harder to ventilate exhaust outside and you’ll be forced to get extra blowers or power to compensate.
The diameter of the duct is important as well and depends on the CFM rating of the blower that is to be installed. Before installation check with the manufacturer as to what diameter the duct needs to be for the blower to operate efficiently. It is also vital that the shape and diameter doesn’t change. For example, if the duct were to narrow during certain parts, it would make the entire ventilation system much weaker and less effective, with greasy buildup also accumulating along the suddenly narrower parts. Ultimately, the size and length of your duct-work depends on the power of the range hood.
Beyond length though, you have to consider where exactly the exhaust will be ventilating to. Here the best choice is outside, but some older systems actually blow the exhaust into another part of the house, like the basement or attic. This technique is not to be recommended since it merely takes the corrosive greasy fumes and places them somewhere else in your home, rather than eliminating them completely. Really, you should ensure your ducting vents everything outside the house, whether outside through the roof or an exterior wall.
Minimize elbows and turns
Finally, in most ventilation systems, your duct-work won’t proceed in a straight line directly from the range hood to outside of the house. Instead, you’ll likely need to employ an elbow or two. The more turns you have in the ventilation duct, the less effective it is, and therefore you should design the duct work with the least amount of elbows or perpendicular angles possible. With any elbow or joints you need to be sure that the duct is professionally sealed too, so no leakage occurs.
Although often overlooked, getting the right duct-work for your range hood is definitely one of the most important steps in installing working ventilation for your range. You should at least plan your duct-work, before actually buying a range hood. Also, if your pre-installed ducting isn’t ideal, and has some of the flaws we’ve mentioned, then you’ll either want to redo it, our get a more powerful range hood.