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Hood vent and MUA calculations--kas? opa?

3 months ago

Hi all: hoping the kitchen ventilation crew is online. I need "validation" on plans for our second kitchen reno. Need to finalize decisions on ventilation based on these specs:

  • Same Lacanche Cluny 1400 we used in the other house. I think about 55K BTU.
  • Custom hood liner from ModernAire, roughly 60"x18" so 7.5 sq ft capture area.
  • BAD duct run, it's the only possible option. 10" duct but three 90 deg turns and a total of about 30 ft of run.
  • Plan to mount a Fantech blower in the attic (currently thinking FKD-10XL plus LD10 silencer).
  • Contrary to my contractor and the HVAC guys ("just run some duct with a baffle into the kitchen") I want to use active MUA. Since none of the HVAC contractors I've contacted out here (relatively rural area) have any experience, I'm hoping to use an off the shelf solution, the Fantech MUAS 1200 system, which seems an appropriate match.

So here are questions:

  • Am I in the ballpark with sizing the exhaust fan given the long duct run (here's the performance specs for the FKD fan: Fantech FKD-10XL performance). Is there a need to upsize? If so, does transitioning in the attic to 12" duct compromise that?
  • The MUA unit would go into the crawl space. Where would you duct the return air? From the crawl space, I could return it to a duct in the floor (easy), wall (harder) or ceiling (harder still). Ny big objection is the blast of cold air in winter across my feet if we duct into the kitchen, say under the range. How far away can I supply the MUA? Is down a connecting hallway (no door) 22 feet too far? I guess adding the MUAH 10/10 would be a partial solution. But there's still hot humid Georgia summer air. What about ducting into the HVAC return duct? I thought there were arguments against doing that.

I'm sure I've missed something. Appreciate any feedback.

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