Which MUA thingy is this?

The simple Broan servo dampers like the MD8T are turned on with standard household current and have no sensors at all. They can be used with other hoods as long as you can tap into the switch that turns on the blower.

But what you're describing toward the end of the message sounds like a much more complex piece of equipment.

It really has no connecting parts to the actual switch.
you punch a hole in the vent duct pipe, insert the air pressure sensor, mount the electronic switch onto the pipe, and run the low voltage wire to the damper that is installed elsewhere in a duct vent pipe to fresh air. This pipe is hooked onto the air return to your furnace.
I'd love to use this with the Zephyr. But Broan is saying no its only for "compatible" Broan Range hoods but the paperworks say only Broans with above 300 CFM - enough to trip the air presssure switch.
But it attaches to the VENT PIPE not the range hood switch.

Here is a link that might be useful: broan make up air damper

It is a rare manufacturer who will rate his components for another manufacturer's products that he hasn't tested.

This Broan MUA scheme appears to depend on a pitot tube in the duct to generate a pressure differential with the household air. The differential air pressure actuates a switch that allows power to go to the damper control. It will probably work if one blows on the pitot tube.

So, it would seem that the requirement is to have enough flow in the duct to actuate the switch, which means that the combination of duct diameter and cfm has to yield the same or higher velocity as the Broan hoods with which this device is intended to work.

kas

Thanks Kas
It does seem quite simplistic and much less $ than the HAE the HVAC guy was discussing. Although we may need this in addition. However the code says MUA and I get the concept. This seems like something that actually just comes on with the range hood.
I do like the Zephyr because I can vent out the back for a bit cleaner ducting solution. So was wondering if anyone has any pros and cons about Best vs Zephyr

Noticed the word 'Universal' in the description. It wouldn't be 'universal' unless it worked with other systems.

There are long threads here on passive vs. active MUA, and may be worth reading for background. The issue is how well the MUA keeps the house negative pressure smaller than about 0.03 inches of water (depending on the appliance). More negative can cause reversal in combustion appliance exhaust leading to CO in the house.

Having no combustion appliances, or having such appliances in their own room with their own MUA source, can alleviate the requirements on hood MUA.

Filtering the MUA against dust, or even against just insects, increases the negative pressure. There may be locations where there are no insects and such filtering is not needed (such as a ship at sea).

kas

kaseki
I've read most I think, of the threads regarding MUA here
but really have not been able to resolve this issue with anyone connected to my build.
HVAC guy : "dont go over 400 CFM total for you house" We'll do a air exchange unit anyway cuz you house is tight.
Kichen appliance store salesman HIGH END by the way:
You really dont need to go any higher than 400 cfm. I dont know what is available for MUA
Inspector: Well code says if the Hood pulls more than 400 CFM you need MUA dedicated to the hood. But it really should match your range. But add in your fireplace and bath vents too.
I just need documentation that you have Correct MUA for your hood if its over 400CFM in addition to the other venting in your house.

My question now is how do you calculate this negative pressure at the before drywall stage when you are trying to determine what !@#$ hood/range/MUA combo to install in the house.?
I did have a different HVAC guy at the bidding stage tell me that to determine the fresh air needs of the house they would do a "blower door test" after drywall. No way to really tell prior how tight the house actually is.
This is Bass ackwards to me and has nothing to do with the negative pressure issue.
AS this should be solved prior to drywall.
What am I missing?

I can vouch for Best being an excellent hood. I have the 58.5" insert recessed into a cabinet above a 36" Wolf.

My situation isn't exctly like yours, but FWIW, I used an inline Broan blower b/c it's the same as Best but less $$.

It's quiet, great capture, looks great, awesome halogen lighting, etc.

ppbenn, if you see this-- what did you end up doing? We are in a similar position now, where everyone is telling us something different. The 400 cfm requirement is new in our county and the contractor is telling us he's betting the inspector won't notice either way (but who wants to be first?) Appliance salesman recommended a Zephyr so that we could hook up only some of the CFM (not sure yet how that works) and then add them back later. I'm thinking we'd rarely need to run it at more than 400 cfm due to our cooking style, but it might be quieter than running a lower capacity hood at full speed.

Don't think this will help the OP but Zephyr has their own MUA "thingy" now

Around $150.00 I think

It looks like I received a question above that I didn't notice. Sorry.

A point that may provide some clarity is that actual MUA flow rate is always balanced with output air flow rate. Seal up a house and turn on your hood, and the air that flows out will be whatever leaks into the house at the negative pressure that the hood fan can manage. It might only be 100 cfm at 0.1 inches of water.

Deliberate MUA makes up for this sealing with a big hole to the outside. Depending on what is in the path of this hole (such as filtering) the output air will increase until it is balanced with the MUA at some new combination of pressure and flow.

The goal is to have enough MUA to allow the hood fan to reach its flow capability at 0.03 or less house pressure. Note that the pressure loss in the hood and ducting is still in play for the hood, so if rated for 400 cfm it may still only move 300 cfm, even with perfect MUA (no MUA pressure loss).

A blower door test is probably the best way of finding out what air flow a given house is capable of leaking as a function of pressure. This can be used to specify the amount of MUA needed. Or, with some MUA system installed, what the overall house + MUA system is capable of doing.

A blower test can be dispensed with if you build a pressurized MUA system capable of moving the total cfm required for all exhaust fans while overcoming calculated pressure losses in the MUA ducting/filtering.

Ultimately though, the final test is determining what house pressure results with MUA when the hood is on high. One hopes that the AHJ would accept a pressure test that shows that the pressure drop is low enough that combustion appliances won't backdraft.

kas

Could mua problem simply be solved be wireing in the furnace fan to the hood fan.via the switch......and not a fancy unit. If its new construction this is easy...and you'll have enough mua for what ever ya want ?...just tossing that out, and kinda wondering.....

"Could mua problem simply be solved be wireing in the furnace fan to the hood fan.via the switch"

I doubt this would pass inspection. Your furnace fan will probably pull in enough outside air for its consumption, but never enough to supply other appliances.

lori - just saw this - we are still building away and getting the house trimmed out so this MUA headache has been put on the back burner.
I bought the Zephyr DCBL Monsoon (I think it pulls around 700 cfm) and the Broan MUA unit. The ducting is behind the drywall but we haven't finished the kitchen yet. I have not chosen a range yet.
My HVAC guy will put a hole thru the wall in the basement under the range and hook up the Broan via a duct to the existing air return to the 1st floor geo unit. This will only remedy the range hood MUA.
We will have a blower door test closer to finish to determine if/which air exchange unit will be needed for the whole house.
This is new territory for our township inspector also but he is up on it and I am sure we will have to remedy a few details. I am putting it in the HVAC guys hands. I know the inspector wanted to know the total of CFM of all fans in house.