I dont know anything about makeup air, our builder said it could be installed in-line with the hood (Independant INBQ) but again our appliance folks said they have never heard of it.

Could someone enlighten me as to what exactly a make-up air system entails?

What viable work-arounds exist? (or are we violating our home warrenty if we try?).

I am also going to be looking for any manufacturer sites and calling Independant to see if they can straighten me out, any other sites that could help me figure out what we need to get done would also be appreciated.

Thanks!

* Does 2006 IRC apply to your jurisdiction?

* How did he compute 3 Pa? How does he know the physics to determine that?

Make-up air is basically a blower system that replaces the air that the hood takes out. You can see its importance, for example, if you think about a fireplace that could have the smoke "sucked" into the house, instead of going up the flue.

Another good source of moderately-priced, high-quality hoods is Prestige.

Chapter 15:
M15001.2 Indoor depressurization. Ducted exhaust systems shall not induce or create a negative pressure sufficient to cause backdrafting of naturally vented, open combustion-chamber, fuel-burning appliances, or create negative pressure in excess of negative 3 Pa. in the immediate proximity of combustion chambers of such appliances.

The builder (their HVAC engineering department) has the A/C capacity and the minimum air flow through the house, since there are minimum requirements for Energy Star certification. With this he can back out how much additional draw would be needed to violate code. 400 CFM was the number they quoted me, without seeing their model and inputs thats all I know.

I dont think the hood is the problem, we have contacted BlueStar, since they are in PA, they make hoods as well and they are the manufacturer of our range, to see what they can tell us about the regulations.

I still cant find much about make-up air systems though everything I've found is industrial.

Your builder seems to know what will and won't pass plan review or inspection. I'm not an inspector, but as I read that, it is saying that the back-drafting or pressure drop is for other naturally-vented appliances, not the range. I don't think the range even falls into the "naturally-vented" category, as it doesn't have a vent to the exterior at all. I would interpret that requirement to apply to, for examples; gas hot-water heater, gas fireplace, gas furnace, but not the range or ovens. With the exception of the gas fireplace, I would be surprised (but not completely so, as I've never modeled it), if a hot-water heater or furnace in your garage or basement experienced significant pressure changes from a 600 (or even 1200) CFM hood on a different level and through several doors.

It might be worth a call to your local building inspection department and talk with what our jurisdiction calls a "Senior Inspector" who can give you guidance. That kind of thing saved us from having to put the gas shutoff in a cabinet (rather than behind/beneath the range) as our code recently changed from "readily accessible" to "accessible" and many local plumbers (and apparently some inspectors) were not aware of the change.

At the hood (e.g. make-up air enters the room at the front of the hood, the exhaust air is drawn out at the rear of the hood)? Somewhere behind/under the range? Elsewhere in the kitchen?

I'm asking because, in a cold climate like PA, I wonder if the need to pre-heat the make-up air (complication, cost) is affected by where it enters?

Also, is it possible that having make-up air enter at the hood, close to the exhaust vent, might make the system less effective at exhausting vapor/grease from the range top some 30" below? As in, the exhaust simply removes the make-up air, leaving the cooking vapor behind?

MUA does not have to come into the kitchen. Mine enters the furnace room and straight into my duct system.

BTW, is 400cfm really enough for a 36" Bluestar???

I do have to say that I am kind of steamed that the appliance people are either disingenuous or ignorant about MUA. Had they let us know in the beginning that this would be an issue, they would have earned some points in our book and we probably would have gone with whoever they suggested for the installation (probably earning them a nice referal fee).

If I hadnt chased this down before the construction started I would have had to change everything and pay an amendment fee on each change to the original plan (nearly everything), which would have cost thousands just on the change fees.

Cooksnews - the 400 CFM definately wouldnt work with the BlueStar, that is why I need to chase this down... if I cant get the MUA worked out I will need to change the range hood to something < 400 CFM which would require a less powerful/smaller range or living with the consequences of not having the appropriate blower. Changing the range would then change the cabinet drawings, granite order, and just about everything else in the kitchen.

You can also use HVR (Heat Recovery Ventalators) or ERV (energy Recovery Ventalators). These exchange air so that in the winter months the warm air going out helps heat the cold air comming in. In the summer vice versa. The difference between a HRV and ERV is that an ERV also echanges humidity. In a cold weather climate the warm moist air in the house will humidify the air that is coming from the outside. In the summer the the humidity will be stripped from the hot air comming in from the outside.

These systems can either be ducted to your forced air system or be independent. Typically you would place vents to capture outgoing air from humid places like bathrooms, Laundry rooms & Kitchens and you would want the fresh air to enter in places like bedrooms. This keeps helps maintain proper humidity as well.

Determine the air flow needed to properly vent whatever you are going to cook on the stove, given your hood size. This may be well above 400 cfm.

Determine the duct size that will keep the air flow, when venting at full power, between 1000 and 2000 feet per minute in the duct.

Determine the exhaust fan that will pull this flow against the negative pressure of the hood and ducting when the house is at the negative pressure you intend to let the house get to before the MUA kicks in. (This may require a blower that is _rated_ 1.5 - 2 X the flow intended to go up the hood.

Design an MUA system that will supply this much air at that negative pressure. The MUA system can be a far more daunting project than choosing the cooking ventilation system.

First, one wants the air warmed in the winter, and maybe cooled in the summer.

Second, the air should be supplied to the kitchen so that it doesn't disturb the upward flow of cooking effluent into the hood. Air that flows down a hall to the kitchen, or is introduced under the stove, or via an opposite wall may be suitable. Turbulent air when it reaches the cooktop is your enemy.

Third, ideally one wants only as much MUA as one is pulling through the hood, bathroom fans, fireplace, etc. This may be the mother of all residential "tuning" jobs to achieve.

What I have planned and partly fabricated to do this is as follows, but I think your HVAC guys can probably integrate yours with your air conditioning. Or if you have the funds and roof space, you might get Greenheck to design and build one for you based on their commercial designs.

I will use a heat exchanger (think car radiator for looks) above a ceiling diffuser that has a 30 x 30 inch opening. The heat exchanger is fed hydronic heat water from my oil burner via a large 013 Taco pump. Pump control will be based on thermostats set to keep the air under the heat exchanger at around 72F AND the air over the heat exchanger above 40F. (I live in NH.)

Electric units are obviously easier to plumb and control, but do require a significant power feed, as a serious kitchen ventilation system may require 100,000 BTU/hr be put into the MUA when the outside is at minimum temperature.

The blower I plan to use for the MUA airflow will be the largest Fantech in-line unit. It will supply air against its duct losses to counteract the probable 1000 cfm I can pull through a Wolf island hood using a 1500 cfm rated exhaust fan, plus the probable 600 cfm I can pull through a 1000 cfm rated NuTone (Broan) exhaust fan pulling air from ceiling registers located above my wall ovens, plus whatever the bathroom fans are pulling at any time.

MUA fan control is _planned_ to be based on the differential air pressure between my attic (open to the outside) and my kitchen. A proportional/integral/differential (PID) controller should be capable of adjusting MUA flow to keep the differential pressure between 0 and -0.02 inches H2O (forget how many pascals that is).

The tricky part in this design is to tune the PID controller parameters so the dynamic response is good without overshoot or oscillation. Simpler control designs, such as scaling the MUA fan power to the hood fan power have their own issues. In my case, with three bathroom fans and two kitchen fans, scaling the MUA fan to the hood fan is not appropriate.

HTH

kas

The new residential code IRC 2009 Chapter M15 REQUIRES that any hood ventilation system now have a makeup air system. This may come as a suprize to people doing a remodel and expecting to get their inspector to sign off.

For EnergyStar certification, you cannot have air that is just brought in from outside as the standard makeup air system because of the loss of heating/cooling efficiency in the home.

sfjeff suggested I talk to Prestige. I originally tried to call the people we would have been buying a hood from, never got a call back after leaving a couple messages. When I called Prestige, they put me on with one of their technical folks and we have been working together to design a hood that works.

Their two best options were:

Using the basement as an air resavoir and ducting from the basement to the hood.

Develop a residential self-compensating hood (as has been suggested above). This sounds good but its pretty expensive just for the fabrication, and I dont believe this includes installation.

(As an example, San Francisco has had rather bizarre requirements on water and DWV piping -- nothing non-metallic; no ABS, no PVC, no PEX -- claimed for EQ safety, believed by most to be a strong union's "contribution" to the codes.)

Honestly, we don't need the make up air...the house is NOT tight, but in a new build it might be a very important thing. I'd certainly follow code.

We basically had to dicker with the building company for essentially 4 months, delaying the start of the house, because they were not allowed (internal regulations), to build a house that did not meet ComfortHome EnergyStar compliance. We ended up needing to request Prestige Hoods to design a one-off self compensating hood for us. The hood performed its regular function and in addition had a seperate set of ducting and 'chamber' that pulled air back into the hood from outside inlet duct ~10' from outlet duct to avoid spitting the exhausted air back into the house. Getting this designed/built/installed has run 4-5x what a regular 1200 CFM hood/blower would cost.

On the other hand, the rest of the kitchen... minus the missing wall oven, has come out great, and so we're looking forward to kicking on the hood at the start of our first meal in the house. Though I'm afraid its going to sound like a train chasing a banshee.

Thanks for all the posts and help!

Andrew

kas

Andrew

But I just bought a BS 36" and I plan to just crack open a near by window (even in winter) when I crank up the Wolf 42" hood I also just purchased. Ignoring the code side of it, will this plan work (and avoid any issue with fireplace or furnace air reversing?). Thanks

That should work perfectly well... thats the real rub of the new code set. There isn't anything wrong with whatever size hood you have if you have a ready source of external air, and a cracked window fits the bill.

You probably want to crack a window on the other side of the kitchen pretty much as far from the hood as you can. This will cause the airflow in the room to be drawn into the hood, better confining smoke and odors.

Andrew

For our more limited kitchen spaces, an ideal would be to introduce the air under all the cabinets so that it enters the kitchen through all the toe-kick spaces, but that would be a project all of its own, and the basement likely would be cluttered by ducting. If the air is entering from an attic space via a roof vent or eve vent, a diffuser that is large and well away from the hood is probably best, preferably in the ceiling of a nearby hall or in another room open to the kitchen.

No matter how the air is introduced, unless one lives where the ambient temperature is always ideal, it will have to be conditioned -- at a minimum warmed when it is cold outside. This adds complication.

If the MUA is passive (no fan), the house pressure will fall until low enough that the MUA flow through the pressure losses of its ducting, plus house leakage at that pressure, equal the hood flow that will also be limited by the negative house pressure. This is a non-trivial problem to analyze for MUA fan requirements. There are MUA systems for furnaces, so that safety issue could be overcome without a kitchen MUA, but the code is the code. Otherwise, a passive MUA must have a pressure loss low enough that the furnace doesn't backdraft.

Another approach is to do the minimum that is required by code and then open a window to supplement it when necessary. Air heating is still desirable, of course, so the window should be where the incoming air has some chance of being tempered before everyone present gets to sample the ambient temperature.

In all cases, avoiding backdrafts of furnaces, water heaters, and fireplaces is important, and the allowable negative pressure will depend on which of these is present. A fan powered oil burner will be a lot more tolerant than a fireplace that depends for its initial draft on the small (0.02 inches of water, I recall) pressure difference between a typical room in a house and the pressure at the roof.

kas

We will be installing a 48" BS with 1200cfm hood in a super tight new home. One advantage is that all appliances are sealed combustion, and the woodstove and fireplace have their own supply air.

Some questions about current MUA thinking:

1) Where is the best location to locate the MUA airstream? Under the range...in the back of the range...in the backsplash on either side of the range...in toekicks?

2) It seems a waste to heat MUA only to have most of it be exhausted. Is it really necessary to warm or cool MUA in extreme climates, if the airstream is properly located?

3) Does it make a difference if MUA is boosted with a fan, or passive, but in either case with a solenoid damper?

Thanks for the help. --Mark