Haven't used either, but so long as the MUA ducting is large enough to not cause significant pressure drop they should be fine. Note that the pressure drop, even without any filtering, will be the sum of the duct loss, intake loss, and kitchen ceiling diffuser loss. These are a function of flow and should be investigated to ensure that the MUA, while working great in supplying the kitchen hood, doesn't end up with a net pressure drop that affects any combustion appliances that use air that is connected to the kitchen.

kas

Thanks for the quick response kas,

Is there any harm in "over doing" the make up air? For example, putting in two 10" passive ducts?

Or, is there a standard formula for calculating loss?

I have a Broan servo damper http://www.broan.com/display/router.asp?CategoryID=100444 that looks just like the FAMCO product and works fine. While the current-sensing option is possible, I run mine right off the blower switch, which has a simple on/off output in addition to the variable output that drives the blower. Yours may have that too.

Kas is the expert, but based on my experience I would see no harm in overdoing MUA, assuming you don't upset the overall heating and cooling of the house. Worst comes to worst you could disconnect one of the servos.

Thanks Colin,

That damper looks great but Broan says it's only for use with Broan hoods.

I'm going to check in on the hood I want and see if it has such an option, that'd be really great.

"Broan says it's only for use with Broan hoods."

Then they're fibbing. They want to convince you to buy more Broan stuff. I'm using it with an Abbaka blower.

The basic model (MD6T or MD8T) has a very simple 24v AC servo, and comes with a transformer that steps down from the standard household 120v AC. So you just need simple household current to operate it - on open, off closed.

Overdoing MUA in my mind would be using ducting so large that you have to seriously modify your house. The lower the velocity of the air, the lower the pressure drops in each of the three minimum components I listed above, so otherwise bigger is better.

But, proportion is needed. Using, for example, 16-inch square duct to fit to a 16-inch square diffuser would be a waste because the diffuser pressure drop would dominate the duct pressure drop. A diffuser of the order of two to three feet square would be called for, because the air has to change direction at the diffuser blades, and hence has to have some pressure drop. The larger the diffuser, the lower the velocity changing direction and thus the lower the pressure drop.

You might not need to box out and reinforce joists to use such a large diffuser, just use a large enough diffuser that the area of a joist passing over it represents a small fraction of the diffuser area.

Hart and Cooley make diffusers in many sizes and diffuser blade configurations, but expect some significant expense for sizes that your local HVAC distributor has to special order.

kas

Duct loss calculators may be found on-line. An intake system's loss (vs. cfm) would likely have to come from the manufacturer. I think Hart and Cooley provide some data for their diffusers. I don't have a catalog at hand to check.

kas

Hi SeaKoz,

I am also purchasing a Wolf hood (liner) with Wolf external blower. Please post the response from Wolf about the Broan damper.

Hi MJOcean,

Wolf's solution was to use _their_ passive air damper. Wait, you didn't know they sell one? Neither did I. They don't advertise it on their website!

It's part # 820071. They sent me the installation manual, I've uploaded it to filebin so you can grab it.

Here is a link that might be useful: Installation Manual

The Wolf system looks very very similar to the Broan, or could it be the same unit ?

my virus software blocks filebin, but do they give you the servo's voltage?

I'm really excited about the CCB Innovations MUA solution!

Refresher/update for those who've read my previous posts: I've ordered a CC 60" range and a 72W x 27D Modernaire hood with 1400 CFM external Abbaka blower. Broan's dampers, but I needed to cobble a lot of pieces together. Shelter has conditioned air and HVAC tie-in, but is complex and not cheap (mid-$1K's). So I'd decided to just use the "crack" method (a window, that is). I live in San Diego, so that wouldn't be too bad... but my wife wasn't having it.

So I asked Trevor at Eurostoves if he knew of a good MUA, and he referred me to Modernaire, who sells the CCB Innovations (http://www.modernaire-hoods.com/MODERNAIRE_2/Makeup_Air.html). The damper (6, 8, or 10") is powered but it's a passive system; negative pressure from the range blower brings in outside air. There are two possible configurations: 1) outside air to diffuser; and 2) outside air to HVAC return air intake.

I was intrigued by the HVAC tie-in option. The HVAC filters the fresh air, and when needed, heats or cools it before pumping it into the house, with no redundant, expensive conditioning equipment. But I was concerned that the separation between the hood's blower and the damper/outside air would result in poor air replacement. So I asked Trevor, and because it was relatively new, he referred my questions to the owner of CCB, Nathan Trant, who called me right away. (Kudos to both Trevor and Nathan for responsiveness!)

So Nathan explained it, and it makes a lot more sense. This is how I understand it (some blanks filled in by me): the range hood blower creates negative pressure, which sucks in the HVAC vent output, which transfers the negative pressure to the return air side. Outside air gets pulled in preferentially over house return air because of negative pressure in the return air. It makes sense to me, anyway.

The beauty of this system is its simplicity. It offers conditioned makeup air at under $500 by using passive equalization from existing blowers rather than adding another blower, and using existing HVAC to filter and condition the air rather than adding heating elements and other complexities.

Kas and others, I'm interested to hear your analysis of this system. Do you think it will be efficient enough to effectively prevent any negative pressure/backdrafting, or do you see potential problems? Thanks in advance.

David

Unless the furnace blower also turns on, some negative pressure has to exist in the house and ducting back to the furnace filter, at a minimum, else no air would move through the furnace from the MUA intake across the filter. Whether this does anything bad to combustion appliances, such as the furnace, is hard to see from here. It would depend on degree and if or how the furnace burner was connected, air-path-wise, to the kitchen.

Turning on the furnace air blower when also opening the MUA damper might compensate for the furnace filter pressure drop.

kas

Kas, yes, that's how it works. The switch assembly gets inserted between the hood and its duct, and it is wired to the furnace using the R and G terminals. When the switch activates at 160-400 CFM (depending on duct size, I'm assuming 400 for the 10" I'm getting), and this turns the furnace blower to the "fan on" position. Again, I assume that the return air duct and the open MUA damper will equalize the negative pressure generated by the blower.

This apparently doesn't affect the auto-on A/C or heat function, so if the MUA lowers or raises the indoor temperature too much, the thermostat will kick on or off the heat or A/C according to the setting. To me this sounds like the most direct and simplest way to get filtered, conditioned MUA.

David

I thought of this as well but this only works for those that live in mild climates.

If you live in an area where the outside air is going to be below freezing, you risk cracking the heater coil.

There are companies here in Canada that sell MUA that also condition the incoming air:

http://www.thermolec.com/images/all/FERflyer-web.pdf

But my understanding is these are over $1000

Here's another site that sells MUA that are cobbled together from various parts:

http://www.epsalesinc.com/products.php

TWGG, I never even knew it was possible to crack a heater core, but then I'm a Californian. I have had frozen coils in my A/C in California during the summer, obviously not for that reason. (I think they said it ha run too long continuously or something.) That explains why you would put heating coils before the HVAC tie-in.

So everybody cool with the dynamics of how this system works? I'm gonna place my order soon. I hope it works as well as it sounds like it works. It makes sense to me, anyway!

David

TWGG, I never even knew it was possible to crack a heater core, but then I'm a Californian. I have had frozen coils in my A/C in California during the summer, obviously not for that reason. (I think they said it ha run too long continuously or something.) That explains why you would put heating coils before the HVAC tie-in.

So everybody cool with the dynamics of how this system works? I'm gonna place my order soon. I hope it works as well as it sounds like it works. It makes sense to me, anyway!

David

Looking at it one way, if the hood pulls 1200 cfm and the furnace supplies 400, there will still be negative pressure. However, considered as a pressure vs. flow device, if the furnace fan provides a pressure boost more or less equal to the pressure drop in the MUA path from outside to the kitchen, then you should be golden.

kas

Thanks, kas. I'm hoping our furnace is good for more than 400 cfm; I'll climb up and look at it on Friday. I'm also hoping the negative pressure will boost the furnace fan. I'm a bit concerned that when the range hood is at max it will boost the HVAC's kitchen registers and cannibalize from the other vents; I guess it'll encourage us to minimize the use of the max setting when we have guests over on a hot (or cold) day.

David

Hi SeaKoz,

Thank you so much for the link for Wolf. Will you be using that unit for your MUA solution? Our house is +/-35 years old and we are installing a 900 CFM external blower, not sure how critical MUA will be under these conditions.

Hi MJOcean,

I haven't decided yet if I'm using the Wolf or the CCB Innovations, I think it'll come down to which one is cheaper as they both operate in the same manner.

My house is a 1956 and I'm definitely putting in some sort of MUA solution. In my previous home which is a 1906, the lack of MUA was noticeable... If the chimney flu was open when the range hood was on, we would get air coming in through the chimney, not pleasant!

MJ, with an older, poorly sealed home, MUA may not be as critical. But if you've weather sealed all the windows and doors, it could make your fan perform at way less than 900 CFM, which would limit its effluent capture.

In another thread Kaseki mentioned measuring the drop in pressure with a "BAPI differential pressure gauge/transceiver". You could try that without MUA and see how it works. Another poster suggested an anemometer to measure air movement, so if it's a lot less than 900 CFM, get MUA, though some could be duct loss, at roof cap, etc.

David

Hi,

Thank you SeaKoz and David. I think I'll pursue the MUA. SeaKoz please write in when you decide which system you decide to use. My renovation (including addition) does not begin until September so I have plenty of time to investigate.

I don't know if it's OK to post prices, so I'll just say the CCB Innovations solution is under $500. (And I'm not talking $499.)

David,

Do you have a part number for the CCB product that integrates with the HVAC system? I couldn't find it on their web site, but maybe it's new enough that they haven't posted it yet.

I'm in a mild climate (Bay Area) and a passive system like the one you've described sounds perfect.

Thanks!

Laura

I don't have a part number, but I posted a link to Modernaire.com who carries the part. Here it is again. http://www.modernaire-hoods.com/MODERNAIRE_2/Makeup_Air.html

Broan makes a damper which is compatible with their hood controls, and maybe others. Basically just needs a wire that switches to 120V whenever the hood blower turns on.

Here is a link that might be useful: Application guide for Broan MUA damper

I'm a little late to this conversation, but I too have this same problem, and trying to see what others have done for a solution. A couple of things I've thought about regarding placing the MUA in your HVAC return air duct, after reading this thread.

As kaseki pointed out with the diffuser, you now have the added resistance of the furnace (strip heater, heat exchange, etc.), an A/C coil, and a filter (dirty or clean) that you'll have to compensate for when sizing the MUA. If the furnace blower kicks on it may not be as big of a problem, but if not the vent hood has to pull the MUA across all of those items.

In the colder climates, even if the cold outside air didn't crack the heat exchanger, the furnace now has to heat the cold outside air, which it will only be able to warm up so much on one pass through the system. Same situation with hot, humid air in the summer. If the vent hood is on for very long, soon the whole how is going to be filled with unconditioned air, as it is being directly pumped throughout the house. Whereas if you just put the MUA vent in the kitchen, a few feet from the vent hood, the outside air has a better chance of being sucked out by the vent hood. And if not, the unconditioned air will have to mix with the rest of the air in the home before making its way back to the HVAC unit.

We have installed the CCB Make up-- on our new (still underconstruction home) We have the a Modernaire Exhaust Hood with an Inline FanTech 1200 fan with muffler. The Make up air vent opens up/turns on every time the exhause fan is turned on. No matter if it's on low or high. I was hoping it would only come on when the fan was turned on Med-high to high...but it comes on immediately. I am sending Nathan with CCB an email asking if there is a sensor to eliminate this problem.

While a less sensitive air switch may be sufficient, you could also use a weak spring loaded damper in series with the motorized damper such that some house negative pressure has to occur to proportionately open the MUA duct path. This would likely require some tuning.

Also, Honeywell may supply differential pressure controlled dampers that might be suitable. You would want the negative house pressure to not fall below 0.03 inches of water unless all combustion appliances are isolated from the pressure drop in the kitchen.

kas