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Thoughts on These Make Up Air Systems?

Allan C | Posted in General Questions on

Scott Gibson’s recent article https://www.greenbuildingadvisor.com/article/sizing-a-kitchen-exhaust-fan?source=W20004EN&tp=i-1NHD-BC-GYU-1aTZpa-1o-YbBQ-1c-rs3-o3kwf-l6r0YHDddH-1mCCKk&sourcekey=W20004EN&utm_campaign=green-building-advisor-prime_eletter&utm_source=eletter&utm_medium=eletter&utm_content=gba_prime_eletter&cid=63642&mid=1455130178  prompted me to renew my search for a proper make up system for a new house I’m building.  Having researched it and read all the blog posts here including Martin’s  https://www.greenbuildingadvisor.com/article/makeup-air-for-range-hoods has led me conclude that there are lots of moving pieces and not a great deal of manufacturer or building code help for this.

I plan on installing a 1400 rated vent hood with an exterior mounted blower motor and have looked at the Electro and Fantech make systems which are somewhat expensive (not prohibitively though).  Broan also makes a fixed 8″ universal damper that is designed to work with Broan and Best Hoods (don’t plan to buy either hood)

I came across this economical system from CCB innovations, but I can’t find many reviews or feedback on it. https://ccbinnovations.com/  From appearances it looks like it should work well.  I can match the size of the intake to the exhaust hood vent size (1o”).  It’s designed to open when it senses flow in the vent hood and feeds air into the home’s cold air return.  It can also be wired to start the furnace blower when the damper opens.  So the make up air will pass through the furnace filter and be drawn in by the furnace blower and be conditioned by the home’s HVAC system if necessary.

Am I missing something?  Seems like a simpler and cost effective solution compared to Electro of Fantech.  I would have to design and place those systems with a separate intake vent in the house.

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Replies

  1. user-7621788 | | #1

    If 1400 cfm is actually leaving the house via the kitchen hood fan, 1400 cfm will not enter through the same size hole without a fan blowing it in. Of course what actually leaves is determined by the exact same amount of MUA coming in somehow. MUA through HVAC equipment might work, but it might cause flue gases to condense where they shouldn't (primary HX) assuming its a 90+ furnace. Furnaces are not MUA units unless in small OA quantities...1400 cfm is ALOT of MUA!

    1. Allan C | | #2

      I doubt that the actual airflow is anywhere close to 1400 cfm. These are marketing numbers with no zero resistance and no exhaust pipe. Even Vent-A- Hood uses effective cfm to market their hoods. They say their 600 is like someone else's 1200. This is one reason why it's so foggy trying to implement a MUA system.

      The electro and fantechs have active blowers, but the CCB is aided by the furnace blower. The Broan looks to be passive perhaps the least effective.

      I'm not quite sure I understand your point about condensate. Variable and multiple speed furnaces have cool air circulating thorough the furnace continuously.

      I've seen so many new houses with professional ranges and hoods ignore MUA requirements. It's bit of a frustrating area to account for.

  2. user-7621788 | | #3

    If the furnace is heating while you pull in cold OA, your return air mix temp might be cold enough to allow flue gases to condense in the primary HX where they will do harm. Carrier says 55 degree minimum RA temp for example. Conversely in the summer, if you bring in warm/humid air, humidity might condense on the outside of the HX where it will do harm, not to mention maybe causing supply grills/ducts to sweat inside the home. Furnaces are not MUA units! A small % of total furnace airflow from outside should be fine (10-20%?) however that may be only 100-200 cfm. You must follow the furnace manufacturer install instructions on temp rise/OA limitations.

  3. Allan C | | #4

    That's good to know, thanks. It's been decades since I did any flowrate and pressure drop calculations, but I don't think 55 degrees will be an issue. The MUA system has a 10 inch duct probably 20 ft in length. It will mix with air from a 20x25, if not larger, return duct. At around 70 deg, inside air, I doubt the mix will drop below 55, but that's something I can check with the HVAC engineer when the system is designed.

    Interestingly enough, Electro just released a non heated version of their MUA units designed to "zone off an existing gas or electric boiler for heat" (Their words). Not much information on that system, so I will have to call them next week to get more info. Could be a very viable and nice solution.

    Just to clarify, there is no intention to have the furnace act as a MUA unit. It's distributing and maybe heating the air from a dedicated MUA system be it the CCB or Electro. I agree with you that an HVAC system with an HRV would never be able to sustain MUA requirements. Thanks for the input!

  4. Jon R | | #5

    1000 CFM when it's 0F outside needs 76k btu/hr to heat it. Will you have that much excess furnace capacity?

    Outside makeup air into the furnace return causes closed door rooms to be pressurized.

    You should use fan powered make up air delivered near the exhaust fan.

    1. Allan C | | #6

      Yes, it's a big house. I expect the furnace sizing to come back at 100k btu/hr if not more, but will need to get all the options and speak with the HVAC engineer. The blower systems require a large electrical heating load which is a disadvantage. The other disadvantage with the blower system close to the exhaust fan is the MUA is hot and humid in the summer

  5. Tom Wheeler | | #7

    Check out NS Builders build. I am planning to do similar with the hood, but with a filtered, fan powered fantech MUA system.

    This is the first one
    https://youtu.be/RJ-WF7gaiXA

    Smoke show to see if it works
    https://youtu.be/u2uVaTMXd_8

  6. Allan C | | #8

    That's a very interesting solution! It's also a bit complex and requires quite a bit of custom work. The intake vent will be challenge to locate away form the exhaust. I would have liked to see them use multiple smoke bombs on the stove to see how the draw was from the cooking service.

    Another issue I can see is that since the intake air is so close to the exhaust and makes up a large portion of the exhausted air, the hood would would have to move a higher volume to have the same effective performance compared to the intake being a bit further away. Looks like it would be quite costly to implement as well.

    But very cool indeed. Thanks for sharing.

  7. Allan C | | #9

    Just an update on where I have landed on this. After a discussion with Electro technical support, I have decided on their packaged air make up system with heat and venting it into the cold air return of the house (One of their recommended installation methods). The heat will only activate if the external air temp is below 50 degrees and the unit is programmable for flow rate. It can sense current on exhaust fan circuits or be wired to directly trigger on exhaust fan activation. There is also a low voltage trigger for the furnace blower.

    The electro unit is considerably more expensive than the CCB Innovations product but is much more robust. The CCB unit is better than nothing, I suppose, but has many limitations.

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