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  • OT - oven hood venting

    A builder has told me that it's common for oven hoods to have filters and as such don't need to be vented outside. Is this true?

  • #2
    Yes - they are known as "ventless" or "ductless" hoods. They are common in large apartment buildings or mobile homes/RVs where vents may not be practical for a variety of reasons.


    Edit: I'm not convinced they ever work as well as the real thing. Plus, the filters get plugged up. If you are thinking about replacing your hood, go with one that vents to the outside. (Remember, it is no longer legal to vent directly to the attic...)

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    • #3
      The recirculating hoods here use carbon filters which you need to replace regularly. My hood that vents to the outside uses metal filters which I can throw into the dish washer.
      If you can vent to the outside that would seem preferable. (unless you live in a cold area, where you will pay the price in your heating bill)

      Igor

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      • #4
        If you live in the frozen assed north as I do, you will find that a tremendous amount of cold air comes in thru that "through the wall" vent. That means plugging it up with a piece of fiberglass insulation for 6 months of the year, rendering it unuseable anyways, and you have to remember to take the insulation out when spring comes. I think that a "through the wall" vent works better, but they are a lot more trouble.
        Brian Rupnow
        Design engineer
        Barrie, Ontario, Canada

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        • #5
          Originally posted by Tony Ennis View Post
          A builder has told me that it's common for oven hoods to have filters and as such don't need to be vented outside. Is this true?
          Yes - I just replaced our over the range microwave and it has a built in vent fan that can be configured either to the outside or inside. The inside path goes through a charcoal filter. The old microwave was the same.

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          • #6
            Much has already been said about the cold north. Ours vents into the garage (actually the fan unit hangs on the wall in the garage). And I can feel the cold by the stove. This also means there is ductwork that is penetrating our garage wall, which in theory should be a fire break of sorts ... so also not good.

            After seeing our neighbors house burn, the Sun morning before Christmas ... that hole in my wall will not be there come spring. Their fire started in the garage and spread from there. They had a couple of penetrations (compromises) in their firewall, and that is where the fire spread to the rest of the house.

            After that, I started thinking about what would happen if ... when thinking about our garage and that 4" hole for the duct came to mind. Is it likely to happen, no. But looking at their house now, it is obvious where the penetrations were in the fire wall ... I will not take that chance.

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            • #7
              The range hoods and microwave/hoods that allow venting on the inside of the house through use of a filter
              are a joke. ALL of them now are made in China, and the quality if awful. The filter is as flimsy as a piece of
              wet toilet paper and the seal for the air flow in the unit itself is another joke of sheet metal origami.
              If you think you can get away without an outside vent hooked up, you are cheap, lazy, and fooling yourself.
              If you fry anything on the range with oil, you need a real working exhaust hood. You also need one with a
              real grease filter. The only ones to get are the kind that are a screen, about a 1/2" or more thick, and
              composed of many layers of expanded aluminum mesh screen. These will trap the grease vapors and
              keep it out of your duct work. They also have to be cleaned very regularly, like every 3 or 4 times that you
              fry something. Use a strong solvent like lacquer thinner to soak them in. The fan hood should also be of
              decent quality construction, with wide flanges to seal against the filter and the fan housing. So many
              are cheap sheet metal that does not isolate the air path, and fills the whole hood ( and/or microwave )
              workings fill with grease, should anything get through the filter (some small amount always will).
              All consumer grade hoods and hood/microwaves are poor quality construction. You really need to look at
              exactly what you are buying. And no 4" round duct is going to work. Use at least 3-1/4 x 10 ducting or
              larger. If you try to use the 4" round, the tiny blower fans with those whimpy shaded pole motors are
              not going to push any air.
              Ask yourself this... Do you want a range hood that actually gets rid of greasy air or do you want just
              to have a hood or microwave that looks nice and is cheap??????? I guess if your wife doesn't cook and
              you eat out all the time, go with cheap and lazy. If you actually cook and take pride in your house and
              kitchen, then buy something good (think more like a dedicated hood and commercial quality blower and
              vent shutters). Look through the Grainger catalogue and see what kind of stuff is available to hook it
              all up the right way. (Or let Larry low bidder contractor hack up your kitchen and install junk that doesn't
              work anyhow).

              ---Doozer
              DZER

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              • #8
                I would think one good bacon session would ruin any "filter".
                Andy

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                • #9
                  JME, but dam near everytime Ive removed one of the "ventless" hoods its full of nastyness and has a good amount of mold in every crack above/behind/around/inside it. Personally, I'd also suggest that those who've had issues with cold air backfeeding into their vented hoods shoot the person who installed it and their likely cheap vent. A quality install with a quality vent on the outside wont leak.
                  "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

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                  • #10
                    i'm not a fan of the ventless style of filters either, but i'm a little perplexed by a couple responses...

                    if you block your exhaust vent with insulation, do you not cook with the stove for those 6 months? or do you just let any grease build up on the insulation and exhaust pipe until spring?

                    everyone i know that has a vented hood (and clothes dryer vent for that matter) experiences a little heat loss through the vent pipe. how would one avoid that? a few aluminum flappers covering the hole in the vent pipe won't stop the cold, but anything that will insulate it isn't likely to be light enough to flip open under the exhaust alone.

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                    • #11
                      My microwave//exhaust fan could be used either way, but I set it up to exhaust into the attic space, which is ventilated of course. The top of the unit has a backdraft damper, nothing more than a sheet metal flapper, that prevents airflow back into the house. We rarely deep fry anyting, we use it more to just get rid of hot steamy air. Actually, if we are cooking and have several burners going and heatb uildsup, the fan comes on automatically to cool down the cook area. So far it has worked fine.

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                      • #12
                        I personally find that a hood that doesn't vent outside is useless for getting rid of heat when canning food in the hot summer/fall (obviously) and is also useless at getting rid of pan fried steak smoke, but maybe 50% effective when frying in general. Maybe only 10% effective when frying fish specifically, may as well save the energy and noise and leave it off.

                        If you're spending the bank's money so a marketing brochure can have a checkbox labeled "oven hood" then its well worth the money even if it only works half way at best. On the other hand if you're spending your own money for your own use then its a complete waste, just spend it on whiskey and women instead. Or, frankly, spend it on tobacco, so at least you can enjoy breathing smoke and fumes rather than spending the money and being annoyed at breathing smoke and fumes.

                        Personally I don't find the noise appealing, so shopping online for a quiet-ish one is probably a good idea.

                        A remarkably low airflow seems to work wonders. What you're trying to ventilate can't be worse than a hot air gun, so I donno about suggestions for something NASA would use for a space shuttle wind tunnel, or five times the size of my HVAC ducts. Think of your clothes dryer duct, that thing handles 3000 watts of condensing steam, so unless you've got industrial cook gear like a KFC would have, something the size of a clothes dryer duct should be, and seems to be, adequate.

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                        • #13
                          Originally posted by brian Rupnow View Post
                          If you live in the frozen assed north as I do, you will find that a tremendous amount of cold air comes in thru that "through the wall" vent. That means plugging it up with a piece of fiberglass insulation for 6 months of the year, rendering it unuseable anyways, and you have to remember to take the insulation out when spring comes. I think that a "through the wall" vent works better, but they are a lot more trouble.
                          You can get a fitting that has a little flap door on it. When the fan is off the flap is closed sealing off some of the down draft, when it's on the air flow blows the flap open.

                          JL.....................

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                          • #14
                            An insulated flap that opens when the blower is turned on would be easy to build and seriously reduce any heat loss. The only thing the filter style hoods do is move the smoke/grease/smell around, they do absolutely nothing towards getting rid of it.
                            And as mentioned, never vent into the attic, mold and moisture damage will follow as well as having the insulation become water logged.

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                            • #15
                              I remodeled the neighbors kitchen which had the vent going into the attic. Even though the attic is vented well it was an eye opener to see the mold that was growing on the underside of the the roof sheathing. Same deal where he had the bathroom vent tucked into the eves. I ran new vents to the outside and he had to have the mold cleaned up. Not as cheap as the duct and vents. In the near North here we insulate the duct or use the insulated type. Unless you live in a wide open space why would you not want to keep your air quality as good as possible? Mike

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