Is makeup air neccessary for a 600 CFM hood?

jplaylandJuly 31, 2012

I'm in the middle of renovating my new old(1982) house. The plan is to put a 42" semi-pro (monogram/viking/...) cooktop and matching hood in/above my kitchen island.

That was the plan until I had an HVAC guy over for an estimate on a new furnace. He saw the demo in the kitchen and told me to make sure to keep under 300 CFM on the hood to avoid pulling the furnace exhaust back into the house.

From what I have found I see three options:

1. Ignore the HVAC guy, do it anyway and see what happens

2. Install a makeup air system. (heated/unheated)

3. Skip the hood and go with a DIY downdraft solution.

Each seems to have it's negative:

1. Dangerous? Against Code?

2. Heated looks to cost $2000+ unless I rig something up myself. Unheated, Minnesota winters, how quick would that cool the house down? How about the rooms closest to the vent?

3. Bad reviews on most of the downdraft products being sold. I'm not sure if my DIY solution would be any better or worse.

DIY Downdraft

I'm planning on putting a breakfast bar counter behind the cooktop. The half wall to support the breakfast bar could also hold ducts. I could install two ducts with vents behind the cooktop. The ducts would go down to the utility room directly below and each duct would attach to a 200 CFM blower motor and be exhausted out the side of the house. I would setup each blower on a separate switch. This way I could use 200 CFM on the left or right side without concern or gamble and go 400 over the whole surface.

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Get the proper and well-performing cfms on the hood you need, and add an HRV (heat recovery ventilator).

Look at Lifebreath or Honeywell

    Bookmark   July 31, 2012 at 11:14PM
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But an HRV wouldn't make up for negative pressure, would it? It would bring fresh air in continually so it'd be replacing the depleted oxygen if it's a gas stove, but if that fan is causing products of combustion to be drawn back into the house, it'd still be an issue, AFAIK.

Here in BC I think 600cfm might be a magic number at which you may need special arrangements.

It would be wonderful to have that kind of extraction power if you can make it work safely.

    Bookmark   August 1, 2012 at 12:50AM
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So, is the risk real or make believe? I mean, there must be hundreds of thousands if not millions of these 600+ CFM hoods installed, and few, even in new construction are installed correctly with make-up air.

I can't find any results for people dieing or being hospitalized for CO poisoning related to a hood.

    Bookmark   August 1, 2012 at 8:46AM
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I have a Viking range and hood, and we love them. My gas water heater and furnace are in an attached garage, and I live in a mild climate area, so my situation is different from yours,


speaking simply from the hood's operating efficiency, you need to have make up air coming from somewhere for the hood to work. Air is stupid, it will come from wherever available - leaks in the house, down an exhaust vent from a gas appliances, etc. Unless you get the model with the remotely mounted motor, the thing gets so noisy that you will rarely use it at full power. We're normally at half, unless we're cooking many smelly things. In those instances, the fan is on high, a window is cracked, and you can't hear yourself think but the exhaust works great.

Stay away from the downdraft models - they don't work. I'm not saying they don't work as well, I'm saying they don't work. We had a friend get one based on a decorator's advice, we tried to talk them out of it, they now regret the decision.

Easiest solution - use it on low or medium for most uses, and crack a window for the brief instances when you need really good airflow because you're using many burners or you need to exhaust stinky smells.

    Bookmark   August 1, 2012 at 12:05PM
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Thanks snidely, I think your "Easiest solution" is likely going to be my solution. I will also make sure the wood burner flue is closed (until I get to removing it.)

    Bookmark   August 1, 2012 at 3:07PM
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It is real.

It is talked about a lot on the Kitchen forum.

The point (cfm) at which you need to provide MUA varies by jusidiction. Usually (but not always) around 400cfm.

    Bookmark   August 1, 2012 at 3:40PM
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