Venting hood range through roof or wall
We are redoing our kitchen hood range ductwork and were wondering what our best option was.
Option 1 is going straight through the attic and up to the roof, about 7 feet, no elbows to a roof vent.
As it is, the vent would be located about 8 feet from the ridge. Is there a minimum or maximum distance from the ridge we have to consider? Or from other elements on the roof?
Our worry here is possible leakage, as we live in a snowy region (near Ottawa, Canada).
Option 2 is going through the attic but then using 2-3 45 degrees elbows to exit through the gable, along the wall. This ductwork would be about 9-12 feet long, but since we’d have 2-3 elbows that count for 5 feet each, we are looking at a 19-27 duct length. Note that the maker of the hood recommends no more than 35 feet.
Could there be an issue with our rake overhanging about 14 inches? Also is there a minimum distance from windows to consider?
Our worry here is loss of efficiency to the range hood.
In both cases, we will completely insulate the ducts.
Any thoughts on the best course of action?
thanks!
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Replies
The sidewall vent under the gable eaves is going to be the most water-resistant assembly since you will not have to contend with rain water running down the roof. I’m assuming your air barrier is at the floor of your attic so in either case you are penetrating the air barrier at the same spot.
Either one can work but my vote is for sidewall. It would be a good idea to replace any perforated soffit vents with solid blocking soffit vents directly about the vent exhaust, so that you are not dumping the vent hood exhaust back into your vented attic. I know for plumbing vent stacks this is a requirement, but I think for HVAC exhaust it is just a good idea.
I’m not an expert but I do recall in my area (North Carolina), the code specifies certain distances from windows, doors, openings so it would be good to check on the specifics in your area.
I'm looking at the 2018 IRC. Chapter 15, Section M1503.3 is the "Domestic Cooking Exhaust Equipment" and it says:
"Duct serving domestic cooking exhaust equipment shall not terminate in an attic or crawl space or area inside the building." But it does not specify any distance away from openings to the building.
- Contrast this with M1502.3 for dryer ducts, which does have a 3' distance to any openings rule.
- General exhaust ducts that fall under M1504.3 also have a 3' distance to any openings rule, I think things like bathroom exhaust fans would fall under this category.
- Plumbing vent pipes also cannot terminate under the overhang of a structure where the overhang includes soffit vents (P3103.1.4).
All this to say there is not a specific requirement that kitchen exhaust hoods terminate some distance away from openings, but again I think it is a good idea. Definitely check if your local jurisdiction has a different requirement though. Re-circulation hoods that dump the air back into the same room are allowed by code, so it would be silly for them to require ducted hoods to have such a strict termination rule.
https://codes.iccsafe.org/content/IRC2018P7/chapter-15-exhaust-systems
I can't think of any reason proximity to the ridge vent would be an issue, but locating the vent directly under soffit vents is not ideal, as they will pull exhaust air into the roof vent space. But even with that, and the additional length, I would still choose the sidewall over the roof. Roof terminations can leak, will definitely contribute to ice dams by melting the snow around them, and if you aren't fastidious about cleaning the filters, you could get grease running out onto the roof.
In talking to some hood dealers and a manufacturer, I've learned that using more than one 90 degree bend is inadvisable for proper operation but are designed to operate efficiently with one bend. More bends would require more exhaust power, increase noise and prematurely wear the motor out. I don't need to do any 45 degree bends so I didn't ask. I think 2 may be alright but not 3.
If venting though an external side wall, common sense dictates that you want it to extend beyond the overhang of your soffit to prevent fouling of that whole area of soffit, wall, adjacent window, etc.
I'm not a contractor but I've heard it said that roof penetrations higher up, closer to the ridge line are better than lower down. I think that's because snow and ice naturally thaws there before it does closer to the eaves. I believe I learned that info here in fact.
Socold,
The less roof penetrations the better, both to avoid potential leaks, and blockages from snow.
Directly under a soffit might be a problem, but even 18" lower would be fine. Range hoods exhaust in the region of 200 to 400 cfm, so the discharge is pushed well away from the wall and beyond the soffit. You can see this clearly on cold days.
Wall, always.
Never the roof, unless it the last option.