Kitchen Vents and Make Up Air

aloha2009July 8, 2011

I didn't think a vent was really necessary since I do no frying other then browning meats. After seeing the grease collect around the area the past several months, I'm reversing my thoughts on that decision. I know this forum is extremely pro venting (and now I'm on board too), so I don't want this to get into a debate over the reasoning behind venting.

I would like to hear what others have done about the issue of the make up air (MUA). If one purchases a heavy duty cfm vent but provides no MUA it severely inhibits the cfm, thus negating the expense of getting the high cfm vent in the first place. Buying a cheaper cfm and providing adequate MUA seems the way to go or better yet have a high cfm with MUA.

What are you doing to provide proper MUA now? How expensive was this part to install? If you aren't doing anything now, what do you plan to do for MUA after the fact (retrofitted)? Or do you plan just to live with your vent as is and just deal with the lower cfm your vent is actually able to work at w/o the MUA?

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Circus Peanut

From what I understand, this is really only an issue with newer houses, since anything older than 20/30 years will (probably) not be airtight enough to matter. (I'm happily corrected on this, of course.)

There have been kitchen forum members with new builds who have installed makeup air systems - it appears to be a better-known issue in climates where whole-house cooling (Texas) or efficient heating systems (Alaska) are common.

I'm sure fan performance is an issue, but I think the biggest reason makeup air is recommended is to prevent backdraft from combustion appliances (gas water heater, furnace, etc) and fireplaces -- pulling the carbon monoxide exhaust back down into the house when the kitchen fan is run.

    Bookmark   July 8, 2011 at 12:31PM
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We crack the window over the sink. My house is not so new that it is air tight.

It works for us, during all seasons.

It is especially enjoyable in the winter when it gets really hot around the stove and oven, the cool breeze feels great! We don't usually have it on "high" for very long so this is why it's not a problem.

btw, I have a 1200 cfm external mounted Viking hood. I don't fry either, but just sauteeing with a little olive oil or butter will cause the baffles to capture quite a bit of "grease". I was so surprised.

    Bookmark   July 8, 2011 at 12:32PM
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aloha2009, in your climate, open a window. Whether it's cold or hot outside.

    Bookmark   July 8, 2011 at 1:02PM
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Circuspeanut. I wouldn't think that "new" of a house would have enough MUA but I'm not an expert, and that's why I have these questions in the first place. We've used an evaporative cooler in houses 15 & 20 years old that need windows slightly ajar to push the air out that is coming in (opposite of what happens with a kitchen vent). When we accidently shut too many windows, the evaporative cooler almost quits working completely (house too air tight). I can't imagine why MUA would be more prevalent in AL and TX since this would be an issue everywhere. I think most of the appliances for combustion air are already in place. I'm thinking the kitchen MUA is a seperate issue (it would be nice to hear from the contractors).

Beekeeper, when I asked about cracking a window many thought I was unrealistic when it's cold. I too live where it gets cold, but something has to be done like your low tech (but very effective) way or the kitchen vent will not work. How much do you have to open your window for everything to work properly?

    Bookmark   July 8, 2011 at 1:07PM
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I had conversations with contractors and architects on the topic. In my area, I was clearly the most knowledgeable on the subject of residential makeup air, although nearly everything I know I learned here on the GardenWeb. There is not much expertise on this topic.

My plan is to do what beekeper is doing -- just crack open a kitchen window in my 1960's era house when I crank my 1200CFM fan.

In the wintertime, the "detector" for whether or not this is sufficient will be the fireplace: If, during cooking, I get poor drafting, smoke in the house, or a CO2 detector goes off, we'll know we need to do more.

If I was really concerned, I probably would have gone with one of the Best by Broan hoods that integrate with their MUA system. If I remember right, that system opens a damper letting air into your existing ductwork creating passive, unconditioned makeup air when you turn on the fan.

    Bookmark   July 8, 2011 at 3:46PM
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I believe that the MUA issue is also code-driven in many areas, so to some extent it is not optional.

I live in a 160+ year old house so the notion of a "tight" is completely irrelevant, if not a joke. I don't plan to have MUA, though not really for that reason.

For me the decision was based on analysis of safety concerns. I heat entirely with wood so I have active fire in my house 24/7 in the winter (I live in northern NY). However, these are in air tight woodstoves that are completely sealed, including the combustion air path so it would take an extremely powerful fan to make mischief there. My domestic hot water is heated in an electric water heater. If my situation was different (even in my leaky house) I would be more likely to consider MUA.

If I had a gas water heater, gas or oil furnace or boiler (without sealed, direct venting), or open hearths, then I think MUA would be mandatory, for safety reasons. While you could refrain from using the fan if you had a fire in your FP you couldn't, as a practical matter, avoid the use of water heater or furnace while using the fan.

My gas range is a 6-burner, double-oven model, with high-ish BTUS. (It's nearly 20 years old, so while it was a fire-breathing novelty when it was new, the BTU-escalation race has since surpassed it. Still, it isn't my Mother's gas stove!) I am contemplating a 900-1200 cfm vent. The range is 48" wide, so size and cost will come into my decision. I don't do a lot of high-heat meat cooking, or deep-frying, but I'm sick of the film left behind by the un-vented cooking I am currently doing.

The question for me is where my cooking style falls on the need for ventilation. Since I plan to buy a liner and the fan guts and make my own cover, I think, but I am not sure, that I could change things out if ny first choice of cfms proves to be undersized. I'm sort of putting off this decision since it's hard to get real answers about this area and I am not using a contractor.

I doubt I would like opening a window in my climate in the winter, so I plan to re-evaluate the situation regarding MUA after the fan is installed. I would need to provide heated MUA, which I think would be very expensive.

I expect homeowners with modern air-handling HVAC systems in modern construction, whether primarily for heating or cooling, would have different needs from a house like mine. The code requirements (and safety concerns) might be the same, but the functional issues may be very different.


    Bookmark   July 8, 2011 at 4:11PM
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In my jurisdiction, make-up air is required for any kitchen vent installation of 350 cfm or greater. I have a 600 cfm unit and required heated make-up air. NOT CHEAP!!!! Like, $8K to install a $2K appliance. And my house is not new. Building codes apply not only to new builds, but to significant renovations.

My MUA system was designed by HVAC specialists. When the vent is turned on, outside air is sucked into my household ducting. The inlet is nowhere near my kitchen, but rather in my basement utility room. When the air is so cold that it would overwhelm my furnace's capability, an in-line electric heater warms it up. By introducing MUA at this location, and conditioning it as required, the entire house temperature is not adversely affected by using the kitchen vent, nor are turbulent air flows established which would give my home that "wind tunnel" ambiance.

    Bookmark   July 8, 2011 at 4:24PM
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Circus Peanut

Aloha, I mention Alabama and Texas simply as examples of climates where folks spend a lot of money & energy to condition the air their homes, and are thus more sensitive to yanking windows open like the rest of us do, so they are more familiar with the technicalities involved. (In old homes, there are no deliberate makeup air systems provided with combustion appliances - we had to do some reconfiguring for the gas furnace when we foamed our basement tight for the first time in its 90 years, for instance. Prior to that, it just drew air in from around the 6 unsealed window frames & bulkhead door.)

I recall there has been a good article or two linked on this forum in the past, on calculating residential makeup air needs. Here are two I've seen go by:

Oversized Kitchen Fans - An Exhausting Problem

    Bookmark   July 8, 2011 at 4:27PM
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Designing makeup air without any determination of how tight the structure actually is is a complete waste of time.

At the very least a blower door test would be needed to determine how much infiltration is already present before hemorrhaging money on a system that may not be required.

The codes have become a way to drive business by adding requirements, and this is the reason many of the code making boards are stacked with representatives of various industry groups.

The entire BOCA (Building Officials and Code Administrators) organization was the ultimate example of this. It has now morphed, but continues its methods.

Simply opening a window IS a legitimate solution in wide areas of the country, yet in their thirst for consistency they try to ram single solutions down everyone's throat.

It has been well known for a long time that vapor barriers are not useful in a wide swath in the US with mixed heating and cooling needs throughout the year.
Yet the code officials continue to place the requirement in the model codes.

The needs of a house in the northern parts of the country are not the same as the south, or even the vast areas between the two extremes.

    Bookmark   July 8, 2011 at 4:36PM
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Please check out the Appliance Forum also. This question comes up a lot over there. If you search around there, you'll see how others have done MUA systems.

MUA is code is many areas. In my municipality, it is required with any hood at 400 or more cfms REGARDLESS of the age or "leakyness" of the house. That hood strength isn't nearly enough for the larger, pro, powerful ranges/cooktops/rangetops a lot of us put it.

My former GC told me he puts in 1200 cfm hoods around here a lot and has never been tagged for not putting in MUA. In fact, he asked the city inspector about MUA and was told that the city has never enforced the code. My 1971 house, while leaky, will be a lot less so with the reno we're doing. He advised me to just do what I want for hood cfms and that it probably wouldn't be an inspection issue. If I feel I need MUA (don't know how I'll judge that) while cooking, I'll crack a window.

    Bookmark   July 8, 2011 at 4:48PM
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Word-on-the-ground in LA is the inspectors care *deeply* about the presence of a damper in the system, but totally ignore the MUA-thing. It sounds esoteric-enough, even if it's on the books, to ask around first. Especially if it turns out to be 4x as expensive as the appliance itself, to install enough MUA. Geesh, cooksnews. That kinda, um, sucks (get it?).

Second breezy's advice to check out the appliance forum on this topic. There are multiple threads with massive amounts of wisdom over there, as well as many folks who provided much of it, still. So impressive.

Also, you can try searching via google, say, this way: make up makeup air -- or some variant thereof. The search engine tells you what forum it's pulling up. Point is, searching via GW is a waste of time; use google in a site-specific way instead.

    Bookmark   July 8, 2011 at 5:10PM
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"Designing makeup air without any determination of how tight the structure actually is is a complete waste of time. "

Hardly! It may result in some overdesign, but some of us would prefer to err on the side of caution, than spend a lot of public resources enacting and enforcing individual codes for individual houses.

I doubt those responsible for my local codes really care what kind of vent hood I buy or how efficiently it operates. But I do like to think they care about how well my furnace works, whether it has enough fresh air available for combustion, and that its by-products rise up its own chimney, instead of through my house and out the kitchen vent.

It may be fun to debate the motivations behind code requirements, just like one can argue about income tax laws. But in the end, whatchagonnadoaboutit???

    Bookmark   July 8, 2011 at 8:00PM
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Don't have much to contribute re: MUA but if you're contemplating a 1200 CFM I will tell you this --it is loud on high. Very loud. I have the Prestige 1200 CFM in a copper hood with a 10 inch duct to the outside. We thought about doing a remote motor instead but that would have put the noise out on the terrace -- not a good option either. The vent works very well and I am also surprised at how quickly it gets oily but also how easy it is to pop out the baffles to clean in the DW. The only real negative is the noise. I don't know if there are differences among the brands but you may want to check this out.

    Bookmark   July 9, 2011 at 7:10AM
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Considering how cost prohibitive it is to install a MUA system, unless your municipality reguires it, I can't imagine putting one in. A homeowner can waste a lot of conditioned air instead of installing one of those systems.

Even if it's not required by code, I got the impression from those who did post that many don't concern themselves that ultimately the expensive vent with super power cfm doesn't really pull off the power they purchased. A few of you indicated opening the window (which seems the only reasonable cost effective way to go) but most seem to just ignore it. I'm going to check out the appliance forum to see what they say about the inefficiencty w/o the MUA. I realize that it's just another thing to think about, but to me it's like buying a fridge that won't cool right unless I open a window twice a day. If you have to do it, you have to do it, code or no code.

Perhaps the extra noise that I read about at high speed may be due to MUA. It's the noise from the evaporative cooler that quickly alerts me that we have closed the house off too much. Opening the window could quite possibly quiet the vent and actually make the vent work properly. Is everyone just using their "broken" vent and thinking it's working?

    Bookmark   July 9, 2011 at 7:57AM
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"Hardly! It may result in some overdesign, but some of us would prefer to err on the side of caution,"

Then omit the hood entirely, windows have worked for a LONG time.

Excessive "caution" can be as bad as doing nothing, but at least you are only wasting YOUR money (as opposed to the Code Administrators that ram through requirements).

    Bookmark   July 9, 2011 at 10:42AM
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@aliris, in fairness that's because California code requires the damper, but not the MUA except for commercial installs... ;) Same here in Northern California---they just checked that we had a damper.

Basically, see if your local code requires MUA, and if it does, proceed accordingly. If it doesn't, you can try it without if you don't have a super tight house. (Our 100-year-old relatively leaky house is fine with a 700 CFM hood in a 235 sf room without any makeup air, but our friends' well-insulated 50-year-old home can't have the furnace and the 600 CFM hood on simultaneously without causing weird gushing sounds---they have to crack a window or door then.)

The extra noise at high speed could be a MUA issue, but it's also very likely to be a venting issue---if you have a long or turning vent or a narrower one, you'll hear it a lot more at higher speeds than one that is straight up and out or wider. That's just about how much air you're moving and how quickly, though. Ours is only 780 CFM on high so it's not a huge deal either way, but we also aren't venting a professional stove. We only use it on high when we're frying/stir-frying/etc. (or when a huge pot of water is steaming). Otherwise, it's typically on one of the two middle settings, neither of which is terribly loud.

As I understand it, the lack of MUA is most likely to affect the operation of the vent if you're in a situation where your vent really isn't getting any air---it's moving the air out faster than it is being replaced in the room, and thus running out of air to circulate. If you're not in that situation because you have a larger space, leaky house, window cracked, etc., you don't have that issue because your vent *is* getting the extra air it needs---just not via a formal MUA system. That's probably what should be your deciding factor. (You can also run the CFM calculations to make sure you really need a 1200 CFM vent, too, if that's what you're considering---some professional high BTU ranges definitely do, but many middle-of-the-road ranges don't need that much.)

    Bookmark   July 9, 2011 at 1:03PM
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This thread is making me wonder if people are checking for their small animals and small children after using their high powered hoods...I'm picturing a chihuahua plastered to the baffles...LOL

    Bookmark   July 9, 2011 at 1:40PM
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Kode, we can't forget to stand back and laugh through all this...thanks for the laugh!

    Bookmark   July 9, 2011 at 8:00PM
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"Then omit the hood entirely, windows have worked for a LONG time."

Yes, but I like to cook and eat, even during the 4+ months per year that my windows are frozen shut.

    Bookmark   July 10, 2011 at 5:45PM
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aloha, sorry, I have not been around over the weekend to see the question you asked.

I crack it about an inch. And yes, it gets cold in the winter here, but.....when I'm cooking on that beast, I enjoy the cracked window anyway and the breeze.

Kode--I always did joke that we have to keep an eye on the dogs when running the vent hood....It is quite powerful, but I love that.

    Bookmark   July 11, 2011 at 10:29AM
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