How To Choose A Range Hood

Question

Mrs. ricepad and I are ditching our over-the-stove microwave as part of a partial kitchen remodel. Eventually, we will be replacing the electric cooktop with a gas unit, and getting new countertops and backsplash at the same time. We will not, however, be getting new cabinets. What should we be looking for in terms of range hoods? The built-in fan in the microwave is pretty freakin' anemic, which is one reason we're kicking it to the curb. I know in general, more CFMs the better, but what is the point of diminishing return? Will a hood that can move 600 CFM be that much better than one that is only rated 300 CFM? Does the cooktop switch from electric to gas require a higher flow rate? And what about noise? Does a higher rating always mean more noise?

Any wisdom, advice, or warnings, 'hounds?

Answer

The general rule of thumb is 100 cfms of ventilation for every 10,000BTUs of total cooktop power. Most mainstream cooktops stay below 60,000 total BTUs (from all burners). You will notice a switch from 300 to 600 cfm -- as long as you all make sure your capture area is also deeper -- the hood should extend to at least 24 inches, and preferable at least 3 inches to the side of the cooktop. Some people will advocate going well beyond this level of ventilation -- but as @janniecooks, then you need to be concerned with MUA. 

As noted, makeup air may be required by code or by necessity in certain jurisdictions. This usually triggers at around 400 cfm. In California, it is not required but in state's like Minnesota it is. However, if you have a very well insulated home and a gas furnace/water heater, you may want to add makeup area to prevent backdrafting of combustion products back into the home. Basically, in a tight sealed home, sucking a bunch of air out can create a situation where the gases from the furnace/heater get pulled back into the home. 

We went from an overhead micro to a 600 cfm hood with no makeup air but with 24 inches of depth over a 60,000 BTU range. It has baffles that you can lift out and drop in the dishwasher. Our home is older so it is a bit more leaky, so we do not have MUA.

Answer

How many CFMs you need depends on what you have as a heat source and a number of other factors which make the hood more or less efficient. CFMs are a convenient way of measuring, but what you are really interested in is air movement at the stove top level. If you have cabinets on each side of the vent that will help with the air draw (makes a tunnel effect), also the distance from the stove top to the hood is critical, the closer to the stove top the more efficient the hood becomes. There are some basic rules for this, typical height range of 26 to 36 inches, again, the closer the better for efficiency, 30" is most typical. You should have a minimum of a 6 inch wider hood than stove top to capture fumes, steam, and heat, so a 36" top needs a 42" hood. Your hood should also extend as close to full counter depth as possible, again, this helps the capture of what you have the hood there to do. You can put a 27" deep hood over a 24" deep stove top to increase efficiency.

More CFMs does not have to mean more noise. There are many different options for hoods and different fan styles and installation techniques to help reduce noise. When we remodeled, noise was a primary concern, we ended up with a 600 CFM Vent-a-hood and it's very reasonably quiet on the low setting and not bad on the highest setting. It has some great features that we really like and is relatively easy to clean and that happens to be my job, so that's important to me. In all cases the motor makes very little noise, so what you hear is air movement, and the type and location of the fan and the filters make a difference here. Our Vent-a-hood has duel squirrel cage fans mounted in the hood and not much in the way of restrictions to create air movement noise. Some hoods use a conventional bladed fan and mount the fan and motor in the attic to reduce noise. Some low cost hoods are just noisy, either because they are designed poorly or because they are fabricated inexpensively or both. Hood noise is measured in Sones, here's a link to Vent-a-hood sound chart by CFM in their units http://ventahood.com/index.php/about/innovation/magic-lung This is valuable as different configurations have differing levels of efficiency and thus differing noise levels. 

Vent-a-hood claims their 600 CFM units are as efficient as many 900 CFM units from other manufacturers, thus allowing you to use fewer actual CFMs and that usually translates to less noise. However, more often than not, 600 CFM will work better than 300 CFM, with all else being equal. Most units are multi speed and you can always lower the fan speed, but you can't increase the CFM beyond it's design and build, so keep this in mind when selecting a unit.

Other than the need to exhaust the gasses of combustion in a gas stove top and the potential greater heat generated by a high end gas unit, the requirements are the same for electric stove top exhausting tasks. You want to remove heat, steam, vapors, grease splatter, etc. regardless of the heat source. If you plan a high end gas unit in the future, keep that in mind when selecting a vent hood, you need to plan for the maximum heat you will have.

Answer

Wow. Just wow. Thanks for all this great information!

Answer

Just to add a little bit to the great info from others, when we did the same replacement you're doing, we went with a 900cfm hood so we could bring our wok indoors. 900cfm might be thought overkill over our GE induction range, but when we're wokking or I'm using it as a deep-fryer (less oil for the same surface area as a dutch oven), we crank it open full bore, because we need to. It suck a lot of air, but that's the plan. For pan-frying and steamy tasks, it runs on the lowest setting and does a great job. 

I take the 900cfm number with a grain of salt, because I've no way to know it really pulls that much, but I do know it works almost as well as or about the same as the big honking hood that was over the 8-burner pro-style range we used in a rental. 

We have no MUA, but live in Florida in an all-electric home. The kitchen is in the center of the house in an open floor plan, which helps, too. 

Ours is a less-expensive unit with steel from China, completely assembled and tested in Ca, from XtremeAir USA. http://www.xtremeairusa.com/shop/
We purchased the hood on Amazon, my dude did the ductwork, including installing the attic vent as our micro-hood was the really, really crappy recirculating kind. One of the baffles was poorly finished and we dealt directly with the mfg, who gave excellent service, staying in touch until we were satisfied. 

I echo the comment about baffles, they're so easy to clean, much easier than a mesh filter.

Answer

Gooster wrote: The general rule of thumb is 100 cfms of ventilation for every 10,000BTUs of total cooktop power.

This is the rule we went by on a recent change from microwave exhaust to standard hood. We had a woefully inadequate setup with a 36" cooktop and 30" microwave exhaust fan when we purchased the house. It at least did exhaust to the outdoors. The cabinets had a coat of grease gum that took a lot of effort to clean off. We couldn't get the extra inches for fan size over cooktop size that Mikie suggests due to existing cabinets, but at least it's matching, we reduced the cooktop to 30" and went with a 30" fan hood, the change has been remarkable. We first purchased a 600 cfm fan but when it arrived the style had changed from the store model. We returned that and had to get something quickly as the contractors were coming. Ended up with a Zephyr Gust 400 CFM, loved the style with curved edges and no controls showing up front to clean around and still adequate for the cooktop. It's a 3 speed and works world's apart from our old setup. We used to have cooking odors linger for days. We had the side windows in the nook converted to opening windows so we can open a small crack of outside air to speed the process if necessary. A worthwhile change, you will love it.

Answer

We had 1000 CFM in our last kitchen. 600 however will handle most gas ranges nicely. The higher CFM are great if you have a grill or high heat wok burner (we had a grill). Getting above 600 CFM, the ducting size usually changes, and that is an added expense. Here in California as noted, we do not require makeup air. We did and still do crack a window or door to the outside when using the hood. The hood operates a lot more efficiently when there is an outside air source.

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How To Choose A Range Hood

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