Switching from a Recirculating Range Hood to a Ducted System
I tried my luck last week on the topic of HRV/ERV in a Northern climate (https://www.greenbuildingadvisor.com/question/northern-climate-hrv-recommendations), and the forum of GBA was exceptionally helpful.
Let’s try round 2.
Since the range hood market seems to take an exceptionally non-science based marketing approach I am looking for the best functioning for my situation which is likely a common one for many people – changing out an old recirculation unit to a properly ducted one.
A couple of notes to explain the situation:
– 1941 House, Halifax, NS Canada
– considered a makeup air system but due to ducting run limitation that has been ruled out.
– House is also not super tight, but it’s getting tighter. Will likely never approach <1.0 ACH.
– plan to open a window and take the heat loss penalty during winter
– stove will be induction (30″)
– ERV system present (max 100 cfm) – not a factor I am considering at this point
– I frequently cook, and sear meat, which creates a lot of steam/smoke
– I will be building a box around it, so looks are not super important, effectiveness is main focus
What I am looking for is:
– How to limit heat loss penalty for new range hood exhaust penetration? (most manufacturers dampers seem to be sub par at sealing…) Do I add additional dampers to combat this?
– General recommendations on size (cfm, depth, width)
– If you have the science to support this, even better.
– General recommendations on positive experiences with products (negative is okay too, but the focus is to solve this issue)
– Cost – ideally I want this solution to be widely available to everyman/woman, if your recommendation features a $5k range hood, it doesn’t solve the issue.
I’ll look to add some detail on products that I will add to this thread as it continues.
Alright GBA – let’s solve this thing…
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Replies
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I'm doing a lot of thinking on this subject as I conjure up designs for a new house... I set my default "solution" to a recirc range hood (going to be on an island) but am keeping in mind that I might want to go with a full exhaust one.
While I'm more of a fan of simple-is-better it might be the case that there's going to have to be some complexity added. I'm thinking that the only way to really get decent sealing to happen is via something that's electro-mechanical. Just tie the power (or relay) to the hood's exhaust fan switch. Here's something that I just ran across (for an idea- no idea of cost as it's for industrial applications):
https://ebaircontrol.com/product/bubble-tight-industrial-damper
Poor filtration of grease is going to cause issues with any damper. Build-up on an electro-mechanical one is going to be a costly defeat. It might, however, take a while before it gets there (depending on the distance from the hood).
Regards to your findings that the recirc hood wasn't sufficient, could you elaborate a bit more? It's seeming that a window-open situation is almost always going to be required for certain types of cooking (my wife's Filipino - try dealing with smells from cooking fish! - I'll have a nice covered porch!) I'm wondering whether my ventilation system (ERV) plus a recirc hood (with good filtration) plus an open window wouldn't be that much less effective than a direct exhaust hood plus ERV plus an open window.
As far as the exhaust vent damper, check out this previous discussion:
https://www.greenbuildingadvisor.com/question/looking-for-good-quality-3-25-x-10-wall-cap-with-backdraft-damper-for-kitchen-exhaust-fan-recommendations
My recommendation there is from Imperial; the particular one might or might not be the right size any given setup, but someone else linked their full catalog:
https://www.imperialgroup.ca/product/venting-flexible-duct/general-venting/
I recently updated my range hood. A couple notes from what I found (sorry no science or proof to back it up):
1) Exhaust to outdoors is better than recirculating for obvious reasons to me. A filter cannot remove CO and many other things, including moisture (a big reason to vent in my opinion).
2) Make the duct run as short and straight as possible (long sweep connectors for turns). This is for both efficiency and sound reasons.
3) Round ducts present less surface area per cross-sectional area than rectangular duct, and allows you to make 90 degree turns in any direction equally well if needed. I used 7" duct which is similar in volume to the 3.25"x10" duct but with less surface area, and I have a left hand bend that rectangular can't efficiently make. (I actually went through the hassle of swapping ductwork from my old unit because it made this strange and highly inefficient left-turn 90.)
4) Capture efficiency is not just a matter of CFM but of the range hood size and location. I have a 30" induction stove as well, but went with a 36" hood. Height-wise, closer to stove is better but obviously there are trade-offs there.
5) In part due to the above, and due to efficiency, I don't think high CFM (above 400) gets you anything good.
6) It's frustrating to compare models via the specs. But I did buy largely based on the sound level specs (sones) and I am really happy with how quiet the Broan BCDJ136 is (note they have many similar looking models but not all with the same sound specs. This unit has 2 squirrel cage style blowers. I was also impressed with Zline specs, but they tended to be pricier). Sound level is really important because it means we can set it to low or medium and still listen to music and talk without noticing the hood hardly at all. That means we use it. Every time.
7) A feature I found I really like is the timer turn off. Pushing a button sets the fan to turn off in 10 minutes. This allows remaining odors to be removed and for the ductwork to dry out, reducing grease runback.
My house really isn't tight, and so I decided to basically ignore make-up air concerns and airtight dampers—choosing to just install the standard 7" round Broan cap (seems fine to me given the relative non-tightness of my house).
Minor note: CO is not a concern with induction ranges.
True that it's not the concern as with gas. And even electric resistance puts out more harmful chemicals (such as particulates I believe) than cooler induction.
Burning of food will still create some CO (does it not?) but it's probably pretty minor, and likely less harmful than other particulates and whatnot.
Either way, 'bad stuff' is being created and a filter isn't apt to remove all of it.
Yes, I think the real difference when you don't use gas is that if you are boiling or steaming something, there's no need to run the hood. But if you are frying or similar, it's still smart to vent.
Yup.
I will say that with the broan model we have, the low is so quiet (whisper), that we usually run it even for boiling to rid of the excess moisture (keep dew off things). The low is admittedly very low cfm (doesn't even quite fully open the damper), but I don't mind that since medium suits general cooking (and is also quiet) and high suits heavier frying (more noticeable sound).
Not trying to sell this particular brand/model (as I'm sure there are other models with similar sound specs) just touting the benefits of a quiet hood.
I should maybe note that circular duct may not always be more efficient, depending on the setup of the fans (the direction they 'throw' the air). I believe the quietest rating for the unit I have is actually with rectangular duct coming out the back (wasn't an option for me). For a short duct run, that may be best, while longer runs perhaps would see benefits from round, depending on the specific unit.
thanks for pointing that out - that elect resistance cooktops give off harmful particulates … could you pls share article(s) with this info pls? i’m planning on an induction cooktop for our upcoming build but thought maybe i should switch to an elect resistance one because of potential high EMF emitted from induction cooktops — no luck trying to find info just yet so any help is appreciated
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Matt. Similar boat here and I’m breaking ground in the next 60 days. Please let us know what your final decision is.
To update:
Right now, I am leaning towards the following:
https://victoryrangehoods.com/shop/range-hoods-on-sale/built-in-range-hoods-for-wood-hoods-on-sale/30-36-inserts/powerful-built-in-range-hood-insert-liner-30-inches.html
- 6-8" duct
- at 8" this can go as high as 750 cfm (high and rarely needed but when searing I don't want the fan to not keep pace)
- 0.7-4.8 Sones
- able to build my own box around the unit
- 19" depth
- reasonable cost v quality ~$600
- cannot confirm quality of damper
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