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Can't Vent Kitchen Hood in Cold Climates?

Posted by mtpam2 (My Page) on
Sun, Sep 11, 11 at 1:25

Not sure where to post this, but wanted to see if anyone else has been told that too much cold air would come into the kitchen from a kitchen hood vented outside. I live in a cold climate (NE Montana). Below zero temps and wind are a fact of life for several months in our winters.

We did not have an exhaust fan prior to this remodel and I was going to get an OTR Micro. When I was looking at them the salesman at the local appliance store recommended recirculating to prevent cold air drafts. Then I found this forum and decided I needed a real hood vented outside. My husband was not too keen on venting outside (straight up and out the roof), but I thought I had him convinced. Then we had our friend (contractor) over to get some advice and he gave the recommendation to use a recirculating kitchen hood too. He said that water sitting on the stove overnight could freeze when vented outside.

Does anyone else have trouble with cold air coming in their hood? Is there something special you do to prevent it? After making up my mind to get a real exhaust hood and vent it outside I hate to think I can't do it. Any help or advice would be greatly appreciated.


Follow-Up Postings:

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RE: Can't Vent Kitchen Hood in Cold Climates?

You have a cap at the end of the duct that closes when the hood isn't running - keeps the cold air out.


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RE: Can't Vent Kitchen Hood in Cold Climates?

You need new "experts". I suggest contacting a HVAC company that understands venting. And, don't use that contractor. He doesn't know what he's talking about. And that's an even worse scenario when he's a friend.


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RE: Can't Vent Kitchen Hood in Cold Climates?

While cold air coming back into the kitchen from the vent shouldn't be a problem, given proper installation of one or more back-draft dampers, all the air that goes out the vent has to be replaced somehow. Replacement may be via leakage through the walls, through an open window, or via a make-up air (MUA) system.

For significant potential ventilation flow rates, wall leakage won't be sufficient, and the flow will be gagged if there is no other opening. In cold weather, open windows are not desirable. Most room heating systems do not have the capability to heat the room air at the rate that a serious hood can remove it.

If the air removed by kitchen ventilation is not made up with a low differential pressure, fireplaces won't work and combustion appliances may back-draft CO into the house.

The standard solution is to provide some form of MUA system. The MUA system has to heat the incoming air. Options include electric coil heating (probably the least complex, but somewhat more expensive in fuel cost), and various forms of heat exchangers running from oil or gas furnace or heater sources.

This should be discussed with the HVAC company.

OTR recirculating systems tend to have inadequate grease and odor filtration for most cooking purposes, but this limitation could be overcome by design if a regular ventilation hood were coupled to auxiliary filtration and ducted back into the living space. I haven't seen any turn-key systems described anywhere, but a suitable one should be possible to design if the space is available in the heated portion of the house. There would be a consumables cost and routine cleaning of some filter media needed.

The goal would be to have a series of ball and mesh filters to remove decreasing grease particle sizes, maybe some furnace filters, and then charcoal filters for odor. A fan designed for a high static pressure loss would be needed. Intense UV could be included for complete residual removal if a practical method for elimination of ozone is available.

kas


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RE: Can't Vent Kitchen Hood in Cold Climates?

Can't vent outside in a cold climate? Baloney. I live in Wisconsin and we also have below zero temps and cold winds in the winter. There is a hinged cap on our vent that blows open when the vent is on, and hangs closed when it is not. It does not allow cold air into the kitchen, and a pot of water would never freeze under the hood. Our municipality had no rules about make up air, but some do. It depends on how powerful of a hood you are planning to install, and what kind of cooktop you'll be using.

Cj


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RE: Can't Vent Kitchen Hood in Cold Climates?

Thanks so much for your input! I knew that it had to be done all the time, but just needed some reassurance. I have read so much about the difference a good hood makes, that I really don't want to go with the OTR micro.

Fortunately (Unfortunately?) we are DIY, and just had the contractor friend over for some advice. Husband will be doing most of it himself. We do not have any makeup air requirements that I know of (will double check) in our small town of 2000 people. Also, our 2 story home was built in the 1930's and there seems to be plenty of extra air coming in! Although less than there used to be since we replaced windows.

We have a 30" electric stove, so I don't think I will need an ultra powerful hood. Hoping to get something in the 400-600 cfm range.

Thanks again for all your responses. It really helps!


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RE: Can't Vent Kitchen Hood in Cold Climates?

You don't need makeup air. Recirculating vent fans are useless.

It seems like you may have other leaks as well, but if this vent is going to be the major heat leak, consider an automatic damper (powered---opens when vent is running, closes otherwise). It works somewhat better than a "flapper" that opens in response to blower air---obviously such a damper has to be very light, and so it can open due to differential pressure on windy days.


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RE: Can't Vent Kitchen Hood in Cold Climates?

We are in a very cold, damp area and I have a Kobe hood with a flapper. I don't deny I hear flapping when the wind really kicks up. I have held my hand under the baffles and do not feel any cold air. We went up about 1 ft and out the wall.


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RE: Can't Vent Kitchen Hood in Cold Climates?

Thanks for the suggestion regarding the automatic damper. I will check that out. I had started looking at hoods, but haven't narrowed it down to any brands yet. I will check out the Kobe hoods. Never had a hood before, and trying to keep the cost down, but get a hood that will actually do some good. Guess I need to do a search for hood threads and get serious about picking one out so I can see how big a project it will be.

Thanks again for all the replies!


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RE: Can't Vent Kitchen Hood in Cold Climates?

Check out Aldes backdraft dampers. They appear to be better built than Fantechs, although I haven't seen them in person yet to confirm. I believe I am going with the Aldes though...


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RE: Can't Vent Kitchen Hood in Cold Climates?

Thanks transy. I will look at both the Aldes and Fantechs.


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RE: Can't Vent Kitchen Hood in Cold Climates?

We purchased a Broan vent cap from local Lowes for relatively cheap. This will go on the roof and has a damper on it to keep the cold air and animals out! We live in Ohio which has its share of cold weather, and have not problems getting vent pipe installed.
The question is, do you really need a vent hood (rather than just an OTR micro? With a small electric range, you probably don't need a crazy big vented hood anyways.


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RE: Can't Vent Kitchen Hood in Cold Climates?

Disagree with ONU Rx.....

Recirculating vents -- in particular, OTR microwave versions -- are so worthless as to be nearly consumer frauds. They make a lot of noise but have pipsqueak capture areas and don't move much air regardless. And what they do move does little more than blast grease/fat/vapor products all over the house notwithstanding their nearly-worthless filters.

If you need to vent, you need to vent to the outside.


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RE: Can't Vent Kitchen Hood in Cold Climates?

Seriously? Someone told you that?

I agree with others....Find a new HVAC person.


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RE: Can't Vent Kitchen Hood in Cold Climates?

Generally, I agree with the advice you have already gotten but would say it depends mostly on the type of cooking that you do. If at all possible, I would recommend venting outside. There shouldn't be a huge difficulty with this in any climate except in the most extreme cases. The as mentioned already, dampers will prevent most of the backdraft problems. If your house is old and not air tight to start with, then the hood is the least of your concerns.

I wouldn't chastise your contractor friend too strongly. I don't know the person and he/she may have just been sensitive to the fact that this is a DIY project and venting outside does require more expertise. Only you and your husband can judge whether that is beyond his capabilities. If your range is against an exterior wall, then it's possible to vent out the exterior wall instead of the roof. Disturbing the roof might be the main concern for a DIY job especially in cold/wet climates.

Good luck.


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RE: Can't Vent Kitchen Hood in Cold Climates?

Thanks again for all you suggestions.

We don't have a grill or do wok cooking, but we do a lot of frying. Fry a lot of meat and cook a lot of soup, etc. Getting rid of the moisture in the air is one of my goals.

Yes we are DIY and I agree, I think our friend thought it would be simpler for us not to vent outside, although I really do think he believes a recirculating fan is "good enough". Unfortunately, our range is on an inside wall, so it is either out the roof, or vent inside. Or turn the vent 90 degrees and run it 5 feet through my cupboards to go out the wall.

Well, I'll continue to research and then see if husband feels it is "doable". Might need to get some help for a couple other things, so if we do, could just get some assistance with the vent also.

Thanks everyone!


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RE: Can't Vent Kitchen Hood in Cold Climates?

My range is on an inside wall too. I ran the pipe straight up an out thru the roof. I let the pipe stick up about 2-1/2 feet. They don't make a flashing for a 8" single wall pipe, so I took a flashing for a 6" class a chimney pipe which is almost 8" in dia and cut the hole slightly larger until I could just push the pipe thru it. I also used a storm collar that was adjustable. I sealed all the joints with roof cement and finished the top off with a chimney cap like that used on a gas fireplace. I taped all the interior joints with foil duct tape, not that cloth junk. I didn't want one of those vent caps that sits on the roof as we get driving rain in the summer and only have a 4-12 pitch. Then there is the snow in the winter, this is Minnesota after all. The pipe is almost at the peak of the roof, so no problems.


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RE: Can't Vent Kitchen Hood in Cold Climates?

Caddidaddy - thanks so much for that information! I will be sure and show it to my husband. I am sure he can figure it out from what you posted. He is very handy. Our roof doesn't have much of a slant either and there was a lot of snow on it last winter.
I really appreciate it.


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RE: Can't Vent Kitchen Hood in Cold Climates?

I reside in NY and above the stove had a hood that vented to the outside. I do not remember it being drafty. The vent or vent cap (not sure what you call it) outside does have a damper that closes.
The vent above the stove was removed.
A microwave was installed above the stove and vents outside. Now in the winter it is very drafty. Cold air is coming in through the filter screen and below the microwave also. It feels like a window is permanently open in my kitchen. It feels so much colder, I do not want to be in my kitchen to have coffee in the AM. The vent or vent cap outside not sure what you call it is closing when not being used.
Vinyl siding was installed on the outside of the building and the vent cap and vent was supposed to be changed and the contractor just didn't bother, or doing what was in the contract
But that is another story or should I say nightmare.
Now it is hard to change the vent cap I was told due to siding being installed.
The microwave was installed about 2 years before the siding, and cold air was coming in so I do not know if that really is the problem.
I am probably getting cold air going out in the summer when the AC is on also.
Who do I call in a HV or a microwave repair?
I do not know what to do?
Thanks


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RE: Can't Vent Kitchen Hood in Cold Climates?

Unless the damper in the microwave oven assembly (if any) is not working correctly, you need a HVAC person. You probably need one anyway because there should be a damper at the house exterior boundary to keep the duct from becoming cold enough to condense water from the air on its exterior or condense water from the exhaust on its interior.

kas


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