GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Secondary Damper for Kitchen Exhaust Vent

C L | Posted in Green Building Techniques on

In a PGH /green and reasonably tight house, should kitchen exhaust have a secondary damper the same way bath exhaust does or is the damper that comes with the hood sufficient?

If a secondary damper is needed for kitchen hoods, will the Panasonic EZ vent work?  The Panasonic EZ vent has been reviewed on this site as an exterior termination with a reasonably good secondary damper for bath exhaust.  However it is plastic and only comes in 4″.
1. Can the secondary damper and termination for a kitchen exhaust be plastic?
2.  Can the Panasonic EZ vent be used to exhaust a 300 cfm 6″ kitchen exhaust (by adding a 6″ to 4″ reducer before the connection to the EZ vent)?
3. If the EZ vent wont work, is there a suggested secondary damper termination combo that could be installed within the soffit area?

The kitchen exhaust hood has a single (flimsy)  rectangular damper at the top of the hood.  The rectangular duct transitions up to 6″ round hard vertical duct.  The 6″ round metal duct takes a 90 above the ceiling and runs about 7′ to the exterior soffit, where it connects to semi rigid flexible metal duct for about 2′, in which it turns down to exhaust out the soffit through a plastic grate with no damper.  There is no option to re-route the duct to terminate the exhaust on a wall or the roof.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. GBA Editor
    Kiley Jacques | | #1

    I’m giving your question a bump. While you wait for experts to weigh in, take a look at this Q&A thread—particularly the comments from Peter Shepherd.

  2. Expert Member
    Josh Salinger | | #3

    CL,

    Our team has been looking for a well sealed secondary damper for range hoods for years without any great luck. If anyone out here knows of one, please let me know. If anyone out here knows of a damper manufacturer, please let them know there is a market opportunity here...

    We have been using the Fantech models suggested by Joshua Van Tol above as these really are the best we can find. I would not use the Panasonic as reducing the 6" duct down to 4" could cause a lot of static pressure and really mitigate the amount of cfm's exiting the hood itself. I would use 6" rigid duct with as few bends as possible and pair it with the 6" Fantech damper, though I understand you may not have a lot of options due to the existing conditions.

    We have taken to sealing and insulating our hood ducts similar to how one would treat an HRV exhaust or supply duct. It will have unconditioned air in it which can create a cold vein and potential for condensation on cold seasons. We use mastic and an insulation sleeve with a vapor closed membrane on the outside of it. Some hoods and layouts work better than others for this.

    We have also used a dampered make up air that turns on automatically with a pressure activated switch. We use the Broan model: https://www.supplyhouse.com/Broan-MD6TU-6-Automatic-Make-Up-Air-Damper-w-Pressure-Sensor-Kit?gclid=CjwKCAjwtdeFBhBAEiwAKOIy57kQSZ9P_8_t0u8rqwrTfnv575_Z4BHPdE50SYXSA_EA7NbVVK5-uhoC158QAvD_BwE. We try to locate it either under the range or in the toe kicks of the cabinets. If it's a slab on grade or this isn't possible we will put it on the ceiling as near to the hood as possible.

    We have been taking the air tightness hit on these systems when we pressurize the house. We have noticed that the dampers work surprisingly well when the blower door depressurizes the house as the dampers get sucked into the seals. For our PH projects we simply make sure we have enough wiggle room to meet the pressurized score- which is averaged with the depressurized score anyways.

    It's not a perfect solution, but it seems like a design problem, not a technical problem. It is also probably good to remember that the benefits of exhausting the cooking and combustion fumes outweigh any penalties one would get from this (relatively minor) air leakage at this location.

    I'll keep my eyes peeled to see if anyone out there has any good leads for a solution here.

  3. Rednets1_MN | | #4

    I had this same question/concern and looked to Europe for an answer. I found a product designed by Naber in Germany called Thermobox 150 (150 mm = 6in).

    https://www.naber.de/en-thermobox-150-s13027/

    I have not installed the product yet, but with it's magnetic 3-wall design seems far more robust and airtight than any inline dampers I could find locally in MN, or frankly anywhere online/in North America.

    I plan to install the Thermobox 150 in all of my HVAC through-wall vents to the exterior: Kitchen exhaust, ERV exhaust, and reversed for the ERV fresh air supply.

    Hope this helps.

    Josh

  4. C L | | #5

    That Naber is an interesting product, but is through the wall vent only. I don't have that option - I need to vent through the soffit.

    The fantech backdraft damper is probably the way to go, but it looks like it needs to be installed vertically and plumb, and that is not realistic working through a 6" hole in an existing soffit. I think I need a damper that is integral with the grill so it can be supported by attaching to the soffit.

    I found one other option at Lowes for a soffit vent with integral damper: https://www.lowes.com/pd/IMPERIAL-8-5-in-L-White-Plastic-Soffit-Vent/3126431
    That leaves me selecting the lesser of two evils between the 4" Panasonic EZ Vent, and the Imperial I found at Lowes. It comes down to better ventilation when the kitchen exhaust is on, or a slightly better damper to stop air leaks when the kitchen ventilation is off.

    EZ Vent Cons:
    - Reduces to 4" which per Josh's comment above, may create too much static pressure and impact the exhaust.
    - Fairly difficult, but not impossible to install in a retrofit application
    EZ Vent Pros:
    - When the kitchen vent is not in use, the EZ vent damper seems like it is fairly reliable and reasonably tight
    - The EZ vent looks better than the Lowe's Imperial, and can be turned to vent outward instead of straight down
    - I have induction cooking (no gas), the hood is 300 cfm at it's max, and some tables indicate you can use 4" duct to vent a kitchen hood up to 400 cfm (although 6" is recommended). My duct run is short, and I only have one 90 before the air hits the 4" dampered section of the EZ vent - the second 90 to turn down the soffit is within the larger portion of the EZ vent, after the damper.

    Lowe's Imperial 8.5" soffit vent Cons:
    - Reviews indicate the spring may not last long
    - Damper may not be as tight as desired or even as tight as the EZ Vent
    Lowe's Imperial 8.5" soffit vent Pros:
    - Seems like the least impact on kitchen exhaust
    - Easy to install

    I may just install the Lowe's product and see how it does. I can always replace it with the 4" Panasonic EZ Vent if it is way too leaky, or maybe someone will come out with a reasonably tight soffit grill/damper system for a 6" duct...

  5. C L | | #6

    Bought the Imperial product at Lowe's. It is better than I expected it to be, but could be better than it is...

    It includes a horizontal butterfly damper that relies upon a spring which may loose tension over time, and sag. The reviews also indicate the spring rusts out. I will probably try to replace it with a stainless steel spring, and have an extra one on hand in case the original sags.

    The 6" neck of the device where the butterfly flaps open is not as deep as the flaps, so the flaps do not fully open. They could have made the neck about 1/8- 1/4" longer which would have let the flaps open a full 90 degrees.

    When the butterfly damper is closed, there is a slight gap between a horizontal flange on the neck and the perimeter of the damper flaps, at the hinge on both sides of each flap. However the flange is a great place to put some thin neoprene which should make this thing much tighter when closed.

    There are tabs that stick out from the perimeter of the neck, apparently intended to create holes in and "catch" the 6" flexible duct. I would rather slide the duct over the neck, and secure it with a worm clamp and tape. I think the tabs will just tear the duct, so I'm considering cutting them off.

    The plastic is sort of lightweight and flimsy - definitely a lower grade of plastic than the Panasonic EZ vent, which I've installed in other areas.

    However, for $13 and immediate availability this device is a cut above the rest and gives a nice secondary damper for a 6" soffit vent.

  6. C L | | #7

    Installed the Imperial product, but now I see that on the Lowe's website, Imperial finally gave an accurate response to the Net Free area of their 6" vent as 5.29 square inches.

    The smallest portion of the Panasonic EZ vent is through the +/- 3.5" flapper, which would have an area of about 9.621 square inches.

    So does the 4" Panasonic actually have more free area and thus greater airflow / less restriction than the 6" Imperial product?

  7. Expert Member
    Josh Salinger | | #8

    Something seems fishy. If the net free area is 5.29 sqare inches, and one divides that by pi, then that would translate to a roughly 1 3/4" diameter hole. I wonder if the information they gave is off...

    1. C L | | #9

      I don't doubt they could be wrong, since they originally posted the free area was .3047 sq in, but the 5.29 seems feasible.

      Their claimed net free area of 5.29 = Pi (1.3) squared. If the radius is 1.3, the diameter is 2.6. So they claim to have a free area equal to a 2.6" hole with absolutely no blockage.

      A 6" unobstructed round opening would have an area of 28.26 square inches. This thing is not unobstructed

      - First, before air gets through the damper, the damper hinge obstructs a good portion of the opening all the way across. Lets call it 1" wide x 6" = 6" si
      - Second, before the air gets to the grill, the damper flappers obstruct part of the grill opening. In the photo from their website they show the flappers only partially open and a gap, making you think it could open more. But the edge of the flapper furthest from the hinged ends hits the grill, stopping the flapper from fully opening. They could have made the neck 1/4" longer to solve for this, but they did not. So that obstructs some air. The second photo posted here is with the thing as far open as it will go.
      - Third, the face of the grill is at least 1/3 plastic, which also obstructs air.

      Panasonic does not publish the net free area of their 4" EZ Vent, but I think it may be more than this 6" vent....

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |