Inspection pains around make up air and my new cc

kurtzicusMay 13, 2012

Hi Everyone,

Thought I would share some of the stories around this sensitive issue for everyone else remodeling. I live in a frequent renovation and new construction town West of Boston. I am putting a 1200sq ft kitchen and master bedroom addition onto my existing 1920's colonial. We just had our first few inspections, and everyone has started freaking out over the cc and the 1200cfm fan I had from Eurostoves.

The cc at 200,000 btu for a 48" version has made all the inspectors nervous. The MUA issue looks to be worse.

In the building inspectors mind if this were new construction completely then there would be a hers rating and that would analyze a lot of this. He is concerned about 1 will the hvac work properly with the MUA coming into the structure (to satisfy code we used an auto damper and a mua vent in the floor under the cc). To satisfy this concern he wants a review by a hers rather of my contractor's manual S calc for the hvac systems. All of this is somewhat new territory for contractors, so be ready to help them a bit in steering if you are committed to a higher end kitchen.

Issue 2 from the inspector is that he is asking us to comply with IMC 09 (mechanical code) 505, 506, 507. I am still trying to get our hands on the details here, but despite the cc being a residential time and despite the hood being a residential hood, I think IMC 507 is commercial duct requirements.

All very frustrating as there are no easy answers here. Anyone else run into these?

Thank you for reporting this comment. Undo

Hi, Kurtzicus, I live in Newton, MA, and am planning a smaller kitchen addition (less than 300 sq. ft.). I am also planning on getting a 36" CC rangetop. I know that I will have to get a 42" hood to meet the code here, but I don't know anything about MUA. Is this something I will need to worry about? Where should I go for more information? What determines whether or not you need MUA?

    Bookmark   May 14, 2012 at 8:51AM
Thank you for reporting this comment. Undo

Below is a link to one of the best discussions of MUA available. The comment section has HVAC, GC's, and homeowners from around the country weighing in. Perhaps you may find a contact on it for Boston. It is a very long but educational read, with much helpful, applicable information (be sure to read the comment thread for the latter).

Hope this helps.

Here is a link that might be useful: Makeup Air for Range Hoods

    Bookmark   May 14, 2012 at 9:18AM
Thank you for reporting this comment. Undo

The key word in the code is the word ''commercial''. The CC range is rated for residential. I would keep pointing that out.

Much of the problem the inspectors are having is: They haven't seen that much cooking power in a residential kitchen.

Here is a link to the IMC

Here is a link that might be useful: IMC

    Bookmark   May 14, 2012 at 9:32AM
Thank you for reporting this comment. Undo

Hi Soibean,

The link that sparklingwater posts is a great one. And not to scare you, but the basic issue is that even if you do everything to what you believe is code, you can still get stuck in all sorts of trouble.

To Bill's point, this is a residential range that my inspector is trying to hold me to 506, 507 in the IMC (which are commercial codes -- thanks Bill for sending).

I've satisfied all the MUA requirements (electronically dampered and approximately equal to the air going out), but the inspector is now requesting a manual S and HVAC analysis of the MUA on the house, and a full review of the ventilation by an HVAC engineer.

It's difficult.

    Bookmark   May 14, 2012 at 10:40AM
Thank you for reporting this comment. Undo

Old Story where camel gets his nose in the tent!!!

Best thing would be to move to New Hampshire, where they
"Live Free or Die" or that's what I use to read on the car license plates!


    Bookmark   May 14, 2012 at 12:15PM
Thank you for reporting this comment. Undo

I'm wondering if I can get by with a 600 CFM hood, since I won't be running anything close to six burners on high (never more than one or two at a time), and won't have a grill on the rangetop. If I did that, would I be able to avoid the whole MUA issue? At what CFM does MUA begin to be a real issue?

    Bookmark   May 14, 2012 at 12:36PM
Thank you for reporting this comment. Undo

The issue is very complex, and since the AHJs aren't engineers in all of the respective areas they have to work in, they tend to be conservative -- that is, get someone else to take responsibility.

The last sentence in the previous message above can't be answered in general. If a house had no combustion appliances (other than the stove), then no matter how tight it was, there would be no hazard from lack of MUA. There wouldn't be much ventilation air flow either, if very tight, but that is a different issue.

What MUA does is keep the house pressure close to that of the outside, which is important so that combustion appliances such as furnaces, hot water heaters, gas dryers, fireplaces, etc. are not backdrafted. A second, but also substantial purpose is to allow the ventilation hood to have a flow rate not restricted by house pressure.

Often there are one or more combustion appliances, and it is important that the house pressure not become negative enough to backflow any of them. This means that the differential air pressure may have to be limited to no more than 0.03 inches of water column.

The MUA path has restrictions that will cause pressure loss, so in many cases an MUA blower is needed to boost the flow. This boost may need control itself, further complicating the air flow into and out of the house.

If the MUA is well balanced, pressure-wise, then it won't affect the air conditioning. But, (!) it is a system that bypasses the air conditioning, and may require heating, cooling, and filtering depending on the needs of the household. If one were to demonstrate that the MUA keeps the house pressure close to ambient for various hood flow rates, then I would hope an inspector would understand that the air conditioning would not be impaired, although its purpose might be partially defeated by cold or warm air being directly dumped into the kitchen.

Ideally, say in a large office building, all the MUA flows into the air conditioning/heating system circuit, so no additional drafts are created. In a commercial kitchen, the MUA is dumped into the kitchen area, and heating and cooling are sized to deal with the flow rate. In a house with existing a/c and heating, the flow in the a/c is not large enough to keep up with the kitchen hood blower, so the separate MUA circuit is added, but only run during periods of serious cooking.

Generally, the heating rates that a furnace can supply via room registers or hydronic heaters are inadequate to deal with high flow rates pulled through windows or an MUA duct in the winter, so additional heating of the MUA is required. (A high BTU oil furnace might be an exception so long as it had a separate loop to a heat exchanger in the MUA path. Commercial MUA will typically use electric coils or gas heat for heating.)


    Bookmark   May 14, 2012 at 3:21PM
Thank you for reporting this comment. Undo

Hi Soi,

Code says 400cfm or less and no MUA required. Problem is that 400cfm for a cc isn't quite enough. But, I know of a job just last month in newton with a 36" cc where the only requirement was a passive "flapper" MUA system and the hood had to have an auto on. This was directly from the inspector as te guys doing my kitchen just did that one.

Good luck, really give that article a read.

    Bookmark   May 14, 2012 at 3:24PM
Thank you for reporting this comment. Undo

I basically did the same thing you did to your house and I'm in Andover. I did a 36" CC Range top. We installed a 8" Braun MUA unit that is tied into the HVAC Return. We really need 2 MUA Units.

FYI, with our master bedroom (above the kitchen), our house is now so tight that we can not properly vent shower steam out (not enough make up air). If you haven't already closed the walls up, I would at least make a provision for MUA in the bathroom, in case you need it.

    Bookmark   May 14, 2012 at 3:53PM
Thank you for reporting this comment. Undo

Wondering why our architect never mentioned anything to us. I would hate to wait for the inspector to show up and tell us we need to remediate. I will look into the "flapper" MUA option. I'll also ask the contractors who bid on the project if they have any experience with this in Newton.

    Bookmark   May 14, 2012 at 4:07PM
Thank you for reporting this comment. Undo

Hi Tony,

Interesting. This house isn't that tight as it's a 100 year old colonial with now a 1200sf addition on it. If I need to add MUA to my new bathroom I can do that as a retro-fir fairly easily. Out of curiosity Tony what CFM fan was your kitchen exhaust?

Soi: I was on my phone before I couldn't give you the link. The active MUA unit is this one:

The passive MUA unit just has a little pressure flapper and if has a negative pressure it swings open, is this one:

It's a MD6 or a BD6. There are other manufacturers.

Tony, I am perhaps in a bit of trouble because I used a 6" MUA given how leaky the house is and frankly, it's a big house. The house has 35,000 cubic feet of air in it, and most of it (certainly more than half) is wide open to the kitchen. With a 1200CFM fan, although big, that means I would essentially be changing the air in my house 2 times an hour (60 minutes/ 35000/1200). That didn't feel absurd to me.

Also, from a Manual-J and heat and cooling load calcuation: most of the MUA is going to come in from near the stove (under it) and go up the kitchen vent along with the effluent, so I'm estimating that perhaps 50% or less will actually be mixed with the air in the structure and therefore need to be heated, since the MUA is introduced close but under/behind the stove.

Tony: that's a great question you can help me with, do you notice colder air when your kitchen hood is on? For me it's a really bad idea to run the MUA into the return-air duct because I have a hyrdo air unit, which is obviously a water coil. That just feels like trouble.

    Bookmark   May 14, 2012 at 4:59PM
Thank you for reporting this comment. Undo

Thanks for the help, TonySak and Kurtzicus. I will definitely check with an HVAC person - I want to do this correctly. My DH is getting scared off and wants me to switch to a 30" residential range instead of the cc, which would be a huge disappointment. I've had my eye on the cc for so long! Could either of you give me an idea of the cost involved in putting in an active MUA unit? Some of the other threads on GW suggest that it is in the $5k-7K range, which would probably be a deal-breaker for us. Assuming we plan for this ahead, we could put the unit wherever it makes the most sense. Our 1910 colonial has a gas furnace, gas-powered water heater, and high-velocity A/C, if that matters. We've made a lot of improvements to seal up the house, so it's not very leaky - who knew there could be a down-side to that?!

    Bookmark   May 14, 2012 at 8:16PM
Thank you for reporting this comment. Undo

One way to avoid backflow is to isolate the furnace and water heater from the air path to the kitchen and put in their own passive MUA.

While it might seem that the MUA will go up the vent with the effluent, in one sense this is more conceptual than real, and in another sense always true. The reason is that the cooking effluent is mostly mixed with room air anyway -- it is room air that carries the water vapor and grease -- so whether you think of the MUA being entrained with the cooking effluent or being part of the cooking effluent, it is needed one way or the other.

It is best to put the MUA into the kitchen to avoid changing the temperature of other rooms, but it is necessary to do so in a way that doesn't cause cross-drafts or turbulence in the rising effluent. Else, the hood has to grow larger.

A large old house will be leaky, and just how leaky (pressure drop vs. cfm removed) can be measured by persons performing heat loss analysis. However, there are reasons why in some seasons one wouldn't like house air leaking out through the cracks, and in other seasons one wouldn't like outside air leaking in through the cracks. These relate to humidity and condensation, as I recall, but I can't be more specific from memory right now.

My feeling is that if the only restriction in your MUA path is the damper, then you shouldn't need a control system and an MUA blower. If you add a furnace type filter (as opposed to, say, a sparrow filter), the pressure drop could be substantial (a tenth of an inch or so) and you will (ignoring house leakage), have a pressure drop too large for the combustion appliances.

Without knowing the druthers of your inspector, it would seem to me that if you could demonstrate at full hood operation with windows closed that the house pressure drop is small enough, he would accept your system as adequate.


    Bookmark   May 15, 2012 at 9:54AM
Thank you for reporting this comment. Undo

The old part of the house has field stone foundation and was built in 1914. Our fan is 1200 CFM. I think people are still figuring out the balance between a tight house and make up air. A tight house seems to create more "new" problems. Even in the old, house bathroom, steam doesn't get sucked out like before. It ruined the paintjob in 3 bathrooms.

We really need 2 MUA units for the hood.. The hood said we needed 2 but we only put 1 in to try it, and 8" Vent is pretty f'n big. When the hood is on the damper opens proportionally to the hood speed. When the fan is on high, it still sucks in air from down the chimney. We get a smokey smell in the winter time. If we're not careful ash will come in. If you put the fan on high and open a kitchen window, its like there is a hurricane outside.

    Bookmark   May 15, 2012 at 10:59AM
Thank you for reporting this comment. Undo

TonySak - if your MUA goes into your HVAC return, how does it affect the performance of the system in summer/winter? Is the MUA separately conditioning the air? This seems like the expensive part of the whole affair.

Kurtzicus - Are you conditioning the air coming from your MUA into your kitchen? If yes, what system is available residentially? If no, are you worried about cold air in the winter and warm air in the summer in your kitchen when the fan is running?

    Bookmark   May 15, 2012 at 1:33PM
Thank you for reporting this comment. Undo

It was recommend by Broan to install like that. During winter if the fan is on, air gets drawn into the cold air return of th HVAC, heated and into the house. I like the idea of getting conditioned fresh air in. During the summer time (heat not on), air still enters and either gets cooled if ac is on, or just passively entrees they house.

I have 2 hvac units. This is going to be the only way to get more make up air into all our upstairs bathrooms too.

    Bookmark   May 15, 2012 at 1:37PM
Thank you for reporting this comment. Undo

Hi Soi,

I'm not conditioning the air coming into the kitchen separately. I am prepared to do this in the future if need be through some sort of ERV or other appliance, but really we were going to run with it as-is and see how it performed as well as how often we used it. This is also the whole argument that kaseki is commenting on -- my MUA is close but not too close to the hood, and not close enough to disturb the cooking effluent, but question is how much of it will just spill in and freeze the kitchen in the winter?

To some extent, if you're using the hood on 1200cfm (high, it's variably controlled) once or twice a week for 30? 60? minutes, is it really worth it to put in a seperate conditioning system? Now, we have a thermostat that has a number of temp sensors on it, and we're putting one in that area of the kitchen, so the makeup air will come in, and the heat will turn on, and the kitchen will be dampered to get a bit more than it needs, but the first floor is a very open plan, so my hope is it's ok.

Perhaps I'm way off base. I'd be happy for people to tell me otherwise.

I do not know the cost of the conditioning ERV or other units, the $5-$7k seemed high, but I would certainly estimate $2-4k after all the requisite issues you'd have to deal with.

    Bookmark   May 15, 2012 at 2:52PM
Thank you for reporting this comment. Undo

Usually, surface cooking will not require full hood cfm, and when it does, the time period will be fairly short unless you are running a barbicue for a lot of people. (Boiling down maple sap for hours would be an exception.) However, I believe if you live in a cold climate such as NE, you will find even 5 minutes of really cold air at 1200 cfm to be very annoying, even if only half is mixed into the general kitchen air.

Although I use a heat exchanger fed by my hydronic heating system (construction not complete), electric coils could do the same job and use modest amounts of electricity over the period of time needed for most cooking, if not modest for short periods on cold days when you are frying.

You might want to check Greenheck's web site for any electrically heated MUA systems that are small enough for your situation. You didn't describe the hood plumbing to the outside, but given a nominal (zero static pressure) 1200 cfm fan, baffles, hood transitions, and ducting, the MUA capacity you need is whatever the bathrooms can pull plus maybe 70% of 1200 cfm. This value will very much depend on how close your MUA system comes to minimizing house negative pressure.

There are some fan curves on Broan's web site that can be used to appreciate how quickly the cfm can drop as the pressure loss across the fan increases.


    Bookmark   May 15, 2012 at 7:20PM
Thank you for reporting this comment. Undo

Bottom line - the MUA concept is for your own safety. You don't want to start pulling CO from your HVAC into the house. I freaked out when I started our reno and heard about this whole concept. So changed to a 350 cfm unit (induction, so can get away with it)
Now, the rules are kind of weird and different states/communities have different rules and regs and enforcement.
Most cold weather states have a MUA rule of over 400. So, if you have 399, you are OK, but if you go to 401 - up the creek without a paddle - you have to install something
Most areas started to enforce this recently and some in the middle of the renovation. (Minnesota is under 300!)
Of interest, many areas don't require ventilation at all - but if you do, stay under the limit or MUA.

Now, we could go onward to smoke detectors - if you make changes to the house, you might need to bring the house to code in this area.....

    Bookmark   May 15, 2012 at 10:44PM
Thank you for reporting this comment. Undo

Kas, all very good and thanks.

A2, I'm not debating the merits of MUA, just perhaps writing another thread on the topic to warn people.

My plan was to
A) supply MUA near the stove
B) oversupply the first floor w heating and cooling capacity by a bit (example more registers, multi zoning, and multi stage equipment)
C) see what happens. Live with it. Adjust, put in a duct heater if we found we needed it, put in supplemental cooling if needed, etc.

I think the inspectors issue is really about arty and back drafting, and that's about my family, so I do respect it! But I think around HERS rating he's mixing up concepts a bit. Bu a blower door test will tell us some pressure data that will help solve this... To be continued,

    Bookmark   May 15, 2012 at 11:15PM
Thank you for reporting this comment. Undo

A great thread. I just wanted to clarify what "active" means.

take this range of options:

1. a duct to the outdoors with a simple flap e.g. Broan BD6.

2. a duct to the outdoors with a servo-controlled damper hooked up to the hood's blower switch e.g. Broan MD6T.

3. a separate blower that pumps air in at roughly the same rate the hood extracts it e.g. With or without additional heating/cooling ("tempering"), e.g. the commercial Greenheck units.

In some conversations I have heard "active" used only for (3), with both (1) and (2) called "passive." Above, "active" seems to cover (2) as well. Clearly it's with (3) that it starts to get expensive.

(I suspect that if you *really* want to be sure and not backdraft something, (3) is the way to go -- (1) and (2) are opening up a little nearby hole, but the pull from the hood is going to affect every available hole to the outside as long as there's a pressure differential.)

    Bookmark   May 16, 2012 at 2:23AM
Thank you for reporting this comment. Undo

(I see my last message had a few errors due to the start of a cold, so please bear with me for the next batch.)

With a big enough MUA hole (duct), and particularly with a fan switch powered damper, the pressure drop to the interior will be low. Six inch duct is probably not enough for 1200 cfm, by the way. I would use 10-inch duct and damper in that case. You may need to go to sources carrying Honeywell parts to get a horizontal damper of this size.

I think that a 3-D set of spaced out electrical coils might allow minimal further negative pressure. I can assure you, though, that if a furnace filter and water-to-air heat exchanger are used, the pressure drop across them will exceed the backdraft pressure (-.03) for unblown appliances like gas water heaters, as well as most fireplaces. An oil furnace probably won't start to backdraft until the pressure reaches around -.06 inches. (However, the damper above the furnace can leak at less negative pressure.)

To go active is a pain, as it is difficult to directly control the MUA blower on the basis of the voltage at the ventilation blower. Throw in a fireplace, bath fans, maybe other ventilation fans and various window open states and the only measure of proportionality is the pressure in the kitchen relative to the outside.

For this, to start, one needs a differential pressure sensor (not a big deal). One needs a shielded port outside that isn't susceptible to wind (a big expensive deal) unless the attic is used as the outside reference, is therefor highly ventilated to approximate the outdoors, and a low cost shielded port is put where the drafts are minimized). Then one needs a controller that powers the MUA blower such that the negative pressure is reduced to near zero.

Now one is in the realm of servo control. A manual setup would require a knowledge of servo control theory and its underlying mathematics, complex algebra. Fortunately, sources such as Fuji sell auto PID controllers that can figure out for themselves how to set up the loop dynamics to achieve a stable system. Fantech, for instance, sells a blower power supply with an embedded Fuji controller.

Unfortunately for me, I need an MUA blower that is larger than the Fantech unit will support, so I have a separate Fuji controller and need to find a suitable power supply that can operate from a 20 mA control loop and power a 16-inch axial in-line fan. TBD.

Looking forward to your success. Suggest obtaining a differential pressure gauge anyway to see what your situation is as you experiment.


    Bookmark   May 16, 2012 at 11:56AM
Thank you for reporting this comment. Undo

Tis a good thread. Sorry for some of my incoherency last night as I feverishly typed before my iPad battery went to zero.

Kas, Colin: active is a pain, I agree too much of a pain and not required by code regardless.

What is a good idea is to get a sensor and/or do a test or two and see how it all fits together. This is the inspectors request basically with the HERS rating (although I still think he's mixing concepts).

We're going to do a 1200cfm blower door test, off the kitchen door, which will simulate the fan (with the fan plugged up) running and have the rater get some technical data on what the pressure is inside & out as a starting point.

Oh, by the way, regarding passive residential MUA venting there is a company out there besides broan with these (10" version of the broan MD6):

    Bookmark   May 16, 2012 at 2:05PM
Thank you for reporting this comment. Undo

Where do you even find the rules for Newton? I keep looking places, doing google searches, but really, coming up with nothing. How do you know 400cfm & less is OK w/0 MUA according to code? How do you know you need a 42" hood over a 36" stove, or does that vary at all? Stove/vent placement is driving the whole kitchen design just now!

Maybe I can just go with 399 cfm (figuring on a Wolf/whatever 30" range, no grill) & add passive MUA? I've got gas hot water/steam heat (one of each) + a gas water heater so I KNOW I could have serious issues. Plus a wood fireplace, but that's less likely to kill us all.

If you don't mind sharing, what're the names of these contractors who work in Newton who actually understand MUA? It really feels, reading around, like so many people don't "get" this, and I don't want to get bad advice that messes up my house.

The bathroom fans do work in my house, it's not that tight. Though best not to close the bathroom door...

    Bookmark   May 16, 2012 at 10:28PM
Thank you for reporting this comment. Undo

meganmca - I'm not sure about the rules for Newton, and for all I know it varies by inspector. Regarding the 42" hood over 36" range, my architect told me that it was a Newton rule (that is unevenly enforced, but why take a chance?). As for 400cfm, I got that number from other discussions on this forum and have no idea what the actual Newton rule is, if any. My architect never even mentioned MUA and apparently never had to address it in any Newton residential kitchen projects before. I am taking it as a safety issue (gas furnace, gas hot water heater) and pursuing it for that reason. The architect suggested calling the city inspector directly. That might be the best way to get an answer one way or another. I am thinking of reviewing my plans with an inspector before proceeding so that I know I'm covered.

    Bookmark   May 17, 2012 at 8:52AM
Thank you for reporting this comment. Undo

In general, the hood should overlap the hot part of the pans to capture the rising and expanding effluent. The amount of overlap would depend on pan size, cooktop configuration, and height of the hood aperture above the cooktop. There is also some expansion angle variation with type of cooking etc. An on-line paper exists on this subject.

This is too much work for most inspectors, or for at matter most inspectees, so the 3 inches on a side overlap rule somehow sprang into being.


    Bookmark   May 17, 2012 at 10:46AM
Thank you for reporting this comment. Undo

Sorry to hi-jack this post but I find on Garden Web "hot" posts are the best ways to get answers, because other individual new topics tend to get ignored.

My question: If you were to put a passive MUA intake vent in your kitchen, where would you put it? Near the range, below the range, behind the range, in the ceiling across the room, etc...?

    Bookmark   May 17, 2012 at 2:06PM
Thank you for reporting this comment. Undo

This a great thread and lots of good information.

Makeup air for commercial kitchens only need to have an 80% replenishment rate proportional to the exhaust rate. And the IRC M1503.4 is rather vague, stating "Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate". So this leaves enough latitude for variations of a single concept. The single concept of the makeup air code enforcement is to provide a point of controlled air infiltration during operation of a high CFM range hood. The principle of mass balance relating to this is "air out = air in". The house is going to breathe one way or another...but if we can cut off the path of least resistance before it draws from a hazardous location then we have supplied a reasonable and effective solution for the makeup air requirement. So, essentially all that needs to be done is to allow for a planned opening that will provide replenishment air at approximately the same rate as the hood exhaust. Like kaseki stated earlier, the intake opening needs to be proportional to the exhaust opening to avoid restrictive air turbulence. Think of it like a culvert during a rain storm. At first the water flow is equal on both sides, but as the water rushes into one side at a greater rate than the other can expel, it begins to dam up waiting to get through the opening. The same can happen with make-up air. If the exhaust/evacuation rate is greater than the point of infiltration, then negative air pressure is still going to be present. Concerns for equal air exchange rates are what confuse and stall most code officials when they are addressing residential makeup air for the first time. And the question is posed for a method of measuring equalized air pressure during operation of the range hood. A simple and easy way to measure for negative pressure during hood operation is to open your front and rear entry doors to allow the internal pressure to balance. Then turn your vent hood on the highest setting and hold an anemometer up to the exterior exhaust opening and measure for optimal air flow rate. Then close your entryways and measure for a pressure drop. Your range hood will not function at its optimal exhaust rate if negative pressure is present. Because if there is less air to evacuate, then the hood exhaust rate is going to decline. If you install a fresh air intake proportional to the exhaust opening that is synchronized with the operation of the range hood, then the pressure should balance. Your house just needs an extra set of lungs to help it breathe while the hood is in operation. Residential makeup air doesn't need to be over-complicated or even expensive.

Takkone - The fresh air intake needs to be installed in an area where the homeowner will not feel a cold or "biting" draft during extreme outside temperatures. Elevated positioning above the upper cabinets works the best. It makes sense in a commercial kitchen to install a makeup air vent at the base of the cooking station, but in a residential setting the homeowner is going to have "frosty" toes in the winter. The same rule applies for behind the cooking surface. Plus, aesthetics play a big role in this location. Kitchens are mostly designed to have their focal point around a decorative backsplash above the cooking surface. And I doubt anyone is going to be happy with a louvred grille mounted in their beautiful backsplash. A common location for a passive makeup air opening is in an upper cabinet that is not used often. Like the cabinet above a built-in refrigerator. The intake can be turned upwards in the cabinet at a 90 degree angle and capped off with a grille that is hidden by the crown molding. Or you can locate an additional register cover on or near the ceiling. Some makeup air systems can even be connected to the air circulation fan in the HVAC air handler unit. This will draw the air through the furnace filter prior to distributing it in the home.

And lastly, "flapper" style negative air pressure dampers are going to cause more issues than solutions. It will be noisy during wind storms and marginally effective as a path of least resistance. A motorized damper in a normally closed position is what best suits this application.

Hope this helps.

    Bookmark   May 17, 2012 at 9:13PM
Thank you for reporting this comment. Undo

Thanks, both of you! I wish I could just look up the rules online, it would be so much simpler...

    Bookmark   May 18, 2012 at 9:55AM
Thank you for reporting this comment. Undo

One reason for the 80% rule for commercial kitchens may be to keep the kitchen pressure slightly negative relative to the dining area. This minimizes cooking odor and smoke egress from the kitchen every time the door to the dining area is opened.

Residential open kitchen designs can't be so easily isolated, so it is important that good effluent capture and containment occur as it is generated. This requirement not only imposes derived requirements on the hood and ventilation system, but also requires that the MUA not be too turbulent at the cooking zone, as turbulence can cause effluent to spill out of the cooking plume and miss the hood. So one wants the MUA to spread out and slow down before it gets to the cooktop.

I can only say good luck in meeting all requirements. Ventilation test kitchens have the luxury of large size and large blank walls that diffuser panels can be put into to keep the MUA laminar and low in speed.


    Bookmark   May 18, 2012 at 10:34AM
Thank you for reporting this comment. Undo

kas - as the resident :-) expert on MUA, what do you think of a design where MUA is introduced above the hood but pointed either toward the ceiling or straight out (i.e., not a curtain of air toward the floor)?

I'm not sure how many options I will have for MUA placement since the molding for my cabinets will go up to the ceiling, so placing MUA in the cabinet above the refrigerator seems like it might not work. I was thinking of introducing MUA behind the hood and pointing it toward the floor, so that it would come out underneath, but it seems like people are getting "cold feet" about this approach.

    Bookmark   May 18, 2012 at 10:58AM
Thank you for reporting this comment. Undo

Try Googling MUA kits. As you can see, there is a dearth of proven, off-the-shelf products that are available for easy purchase or widely used. The ideas and codes have gotten very far ahead of reality. There is really no excuse for consumers having to make this stuff up as they go along.

    Bookmark   May 18, 2012 at 1:11PM
Thank you for reporting this comment. Undo

If you use a diffuser that directs the air across the ceiling so that it curls around and spreads out before returning toward the cooktop, then that should be ok. I used the ceiling at the far end of a hall visible to the cooktop to introduce the air with the hope that it will expand and slow down on its way to the kitchen. Mine is heated, although not, yet, powered. My kitchen is now open to the LR and hall. A closed kitchen would pretty much limit one to the ceiling, especially if the source were the roof.

Note that the intake on a roof has to be at least 10 ft from the exhaust, and chimneys, and DWV vents, etc. I would also put it lower and upwind.

I'm thinking of turning my "expert" mantle over to Nateman72 and retiring. ;)


    Bookmark   May 18, 2012 at 7:40PM
Thank you for reporting this comment. Undo

Hi Kurtzicus,

Do you have any updates on your MUA situation? I hope your inspector backed off and educated himself.


    Bookmark   May 28, 2012 at 11:10PM
Thank you for reporting this comment. Undo

Hi All,

So last week we had a BPI inspector and HERS (they do energy/sealing/blower door-type testing) inspector to the house. This is covered by BPI and not by the HERS/Resnet system.

He did a blower door test at:

a) the design 1200 cfm of the kitchen exhaust
b) the maximum he could do

while simultaneously measuring pressure both inside the house and outside. All windows were closed, any holes taped over, and the MUA was closed. There is apparently a BPI standard here on combustion appliance limits versus depressurization: check out page 14 -

In any case, the test was $300, and included a measurement of the cubic feet of air in the house versus the allowed limits/air changes per hour, and depressurization limits in the above standard. Long story short we passed with no problems at all, it's an older somewhat leaky house and his analysis was that at 1200cfm NO makeup air was required at all, and given that we had installed a 6 inch damped unit we'd be golden.

He's written a memo for the inspector, which I have yet to bring by, but I will see how it goes.

HOWEVER, the inspector has also asked for a Manual J and Manual S on the building because he is concerned that the additional heating and cooling load of all the MUA will mean that we're undersized. The HERS part of the guy I used had a good chuckle at this, because it's more of a fundamental question if you would design the heating/cooling system for a fan that you're going to intermittently use in a residential kitchen.

Food for thought. I'm going to try and convince the inspector to skip the manual J/S analysis now that the combusition safety has been proved.

    Bookmark   June 13, 2012 at 9:13PM
Thank you for reporting this comment. Undo

I am resurrecting this a bit to keep a log of where I am.

I took delivery of my new cc and my modern air hood some weeks ago from Eurostoves, had it installed, and got to the point of final inspections just now.

Big problem: inspector not happy with the cc: too much power for a residential kitchen. Not happy with 1200cfm fan still, so we've resized to 400cfm, which everyone has convinced me is the right thing to do.

I warn everyone: be very very wary of the cc's and MUA issues and inspector's in general around the issue of the stove design/setup. Great stove, but I'm not getting any progress on some key issues, including whether or not my hood has an "auto on" feature tied to the operation of the stove, and how to demonstrate that auto on feature.

I'm afraid I'm going to end up scrapping my hood and cc at a point in the process where it just stinks.

I haven't been a first time poster on this forum, so please don't think I'm saying this just to be negative about a product.

But, at this point in the process I'd warn everyone of these issues and tell you to be prepared for some nightmares around how the hood works with the stove and how the MUA comes into play and the fact that despite all my planning and energy auditing and engineering can still end up out of luck.

    Bookmark   July 23, 2012 at 6:00PM
Thank you for reporting this comment. Undo

Hi, kurtzicus. I'm glad you came back with an update, sorry to hear how difficult this has been for you. Would you be comfortable sharing what town you live in?

We have just put our project out to bid. So far, of the four highly-recommended contractors we have interviewed, not a single one knew anything about MUA. When I described the issue, one suggested I switch to induction, another suggested cracking a window. Not a single one has ever installed MUA, and I'm certain they've done high-end kitchens with powerful ranges. Pretty discouraging! At this point I am seriously considering a switch to induction and using a lower cfm hood just to avoid the whole issue.

    Bookmark   July 23, 2012 at 7:42PM
Thank you for reporting this comment. Undo


    Bookmark   July 24, 2012 at 8:58AM
Thank you for reporting this comment. Undo

I'm going to guess that the town might be Needham. I used to live there and I know people who still live there and have either recently renovated or torn down and rebuilt there (within the last five years). They have a reputation for being tough and have VERY conservative interpretations of the codes. This is just my hunch based on nightmare stories from these friends about how projects dragged on because inspections. There is a backstory for the conservatism, but I don't have all the details.

I don't think kurtzicus' story is an indictment on any product, because it would apply to across all brands with similar specifications. But what it does do is arm anyone doing a renovation with information about potential issues that may arise, whether or not they are warranted.

kurtzicus, I wish you all the luck in your project. Hopefully it'll all have a good ending and you won't have to scrap your plans.

    Bookmark   July 24, 2012 at 9:38AM
Thank you for reporting this comment. Undo

kurtzicus..... Don't give up yet, if you care to give me a call I will arrange for Capital and CCB innovations to get involved in an attempt explain to your inspector that things can be resolved to everyone's satisfaction.

    Bookmark   July 24, 2012 at 10:14AM
Thank you for reporting this comment. Undo

It would really bother me if an inspector said, "You can't install a stove designed for a residential setting in a residential setting."

    Bookmark   July 24, 2012 at 2:34PM
Thank you for reporting this comment. Undo

The problem is that the inspectors need to understand MUA before making sweeping decisions that dramatically affect the house holder. That is why if Capital and CCB make contact with the inspector things may get resolved.

    Bookmark   July 24, 2012 at 3:19PM
Thank you for reporting this comment. Undo

Obviously, the inspector is well beyond his competence--both intellectually and legally. MA code does not even require a hood at all. A hood is not a piece of safety equipment.

That said, of course these idiots can make trouble and expense for homeowners.

So install a cheap range and hood from Craigslist and do what you want once your home is moron-free.

    Bookmark   July 24, 2012 at 8:35PM
Thank you for reporting this comment. Undo

I like the idea of the craigslist stove and swap later. I tend to get very frustrated on things like this.

But alas I'm trying to work the system properly to succeed. I will happily let you know the town, just give me a few weeks to get it all resolved. I don't want us to be bad mouthing my inspector while I'm still trying to get it done. It's a suburban Boston town just on 128 near rt 2. Thing about the inspector is that I respect the guy for trying to make sure all is safe but auto ons and grease clear outs on ductwork and the wanting my MUA install validated by building sciences energy raters has all come back ok, but at the end of the day he just has a nasty gut reaction I think to a really big btu stove in a residence and all the conundrums that come with it.

Trevor I will give you a call, you and Eurostoves have been great but I haven't engaged you with this issue yet because I didn't want to be too much of a bother, but seems like it's time to get some reinforcements.

    Bookmark   July 25, 2012 at 3:43PM
Thank you for reporting this comment. Undo

If it's the "Honest Abe" town, then I feel for you. The inspector just started there a couple of months ago. Guess where he came from? Needham. How do I know? My friends in Needham.

    Bookmark   July 25, 2012 at 8:39PM
Thank you for reporting this comment. Undo

Well, describtion of a town kurtzikus is mentioning leads me to believe it is one jscout is also mentioning and it just happens to be town we are moving to.
Really would like to hear what the resolution to the inspect issue was, since we have about the same setup in mind.

    Bookmark   July 7, 2014 at 10:37AM
Sign Up to comment
More Discussions
DCS double wall oven--reviews?
I'm in the market for a double wall oven and saw a...
New Bluestar RCS model - Any Info? (RCS366BV2)
Most of the 36" RCS models are RCS36IRV1 right...
Need feedback on KOBE Range Hood
Hello! I'm looking at buying a KOBE range hood. The...
Ordered my BlueStar!
I ordered and paid my deposit on my BlueStar on Saturday....
Debbi Branka
How much Hood CFM to get for Wolf's 6-Burner Rangetop?
Let's say I use all 6 burners at once sometimes (not...
Sponsored Products
Sarah 22-Inch Stone Decorative Pillows, Set of 2
$70.95 | Bellacor
Madsen Leather Bumper Chaise - Brighton Volcano Brown
Joybird Furniture
Mosaic Tile: MS International Building Materials Rustique Interlocking 8 in. x
$12.98 | Home Depot
Chelsea Ivory and Ivory Round: 5 Ft. Rug
$183.95 | Bellacor
Judy Royal Blue Lamp
$140.95 | Bellacor
Roddy Chair - Lucky Turquoise Blue
Joybird Furniture
Besa Milo 4 Pendant 3JV Light with White Frost Glass - 3JV-MILO4WF-BR
$526.50 | Hayneedle
Besa 1SW-1779HV-SN Halva Mia Wall Light - 1SW-1779HV-SN
$180.00 | Hayneedle
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™