TL;DR: Have kitchen hood, need to vent outside, Roof and walls are not an option.


My only options at this time are:


1. Recirculate

2. Take over a Soffit Vent and Duct it out here.


I've reserved myself to taking a 6" rigid round duct into a 3.25x10" duct and flashing it into the soffit vent I'll be re-purposing.



I wanted to go through the roof but that option is off the table.







Unit Specs: 900CFM blower. Approx 20 LF of ducting. Duct Mastic: Check. Aluminum Duct Tape: Check.



Thanks for the help....

900 CFM? Must be a higher-end hood.

Typical vented residential hoods can easily be vented with a soffit grille. I believe some supply house even have boot boxes that connect to the soffit grille with either 10x4 or 7" round duct. I'm impressed you have mastic AND tape, most folks ("contractors" included) would use one or the other, but not both.

Mastic is good to paint on big joints, but I've had to go into too many crawl spaces because my HVAC sub fucked up the jointing to ever want to be bothered with it. I'll do Both and do it once.

 

Funny part is that anyone who worked for an HVAC contractor probably started out with a "pookie" brush, sealing the outsides of joints and buttering up the insides prior to connection.



At the very least you know you won't be blowing greasy air into your attic.

Yep. And they still end up with leaks under the insulation.... It really fucking blows my mind. I will be Mastic'in the joints and then sealing it all with the good 3M aluminum tape for good measure

 


I plan on taking a sheet of duct and cutting a 3.25x10" slot in it and inserting my 3.25x10 duct into that, nipping the end to turn it back up to the sheet (mastic+tape sealant) and then placing that over the soffit hole. I'll have to remove the micro-mesh soffit webbing and replace it with a larger mesh to avoid gumming it up with grease / fumes, even though my unit has Grease-channel traps at the induction point.


Any recommendation for a 6" Round or 3.25x10" rectangular Backdraft damper?


It will have to be Spring or counter-weight closed as the damper will be Horizontal or wrong-way vertical for Gravity dampers to function.

At 900 CFM you probably need makeup air to be up to code.

What hood do you have? I bought a Zephyr Typhoon when I had my kitchen redone 3 years ago.

I have one of these: http://www.xtremeairusa.com/shop/product_info.php?cPath=3&products_id=747

 

Those look nice! I bought the Zephyr because I wanted some power but I have the rectangular duct opening right behind the hood. I'm in a condo and cant make structural changes.