I'm in Southern CA so make up air isn't an issue. I'm ok going with lower CFM but then it gets louder if we run it at higher speed. What CFM do you have?

smm5525,

Why would make up air not be an issue in SoCal? Did you mean that you did not need to worry about warming the makeup air? Makeup air is about depressurizing your home when using a vent hood and potential back drafting from other gas fired appliances in your home. Do you have any other gas fired appliances in your home?

I would look into an insert that is 24" deep, otherwise it will not cover your front burners. That is much more important than increasing the width of the hood.

We won't have any gas fired appliances on at same time or if we did we can open windows. That's my understanding re: make up air.

I think 22" deep hood will be fine. We aren't too concerned with completely covering the cooking surface. Just don't want a monster sized deep hood :)

smm5525,

The understanding the makeup air is about open windows is incorrect. Your hood is expelling air out of your home at 1200CFM. Depending on the size of your home, you could cause a back-draft or depressurize your home in a short period of time. Depressurization will cause windows to break and back draft any gas appliance into your living space. This is very dangerous. Opening a window will not replace 1200CFM of air every minute, only a mechanical system will do this. You would need 150mph windows to replace 1200CFM. I am not sure what size window you would need to get the 150mph air into your space.

Makeup air can be uncomplicated. There are a few options that don't deal with warming the air which you don't need in SoCal. You may want conditioned air but you should not have too much of a problem since you don't have a ton of humidity to worry about. Broan has a unit that is activated based on turning on the hood and is linked to your central HVAC if you are using one.

Give a little bit of information:

1. Do you have central HVAC?
2. What is your style of cooking? Wok cooking, indoor grilling etc
3. What is the largest capacity burner on your induction cooktop?
4. What is your budget?

Good luck!

1) we have central HVAC. Two story 3500 sq ft home. I thought my contractor said we need not worry about make up air but I think they were going to look into what's required.

2) sautéing and searing. No frying no indoor grilling.

3) see photo below

4) budget we are flexible but trying to not spend too much on this. We've lived without a proper hood so far and it's just not a huge priority for us. I don't ever see running it at highest speed. I read higher CFM will allow operating at Lower speed for less noise than getting a lower CFM running at higher speed.

OK, let me make an observation; if one had a displacement blower (like the Rootes blower on an unlimited dragster) one might be able to pull 1200 CFM against a significant back pressure, or even possibly lower house internal pressure to the point that a window would break. For normal kitchen hood blowers, however, slight pressure differences across the blower cause a reduction in flow rate. At some point modest back pressure will kill all flow and the window is out of danger. How modest is modest?

For example, in the case of a Broan-NuTone 801642, (used by Wolf), its rated 1200 CFM at zero static pressure air flow rate drops to 700 CFM at 1 inch of water column differential pressure. (Approximately 407 inches of water column equal one atmosphere, so one inch is 0.0025 atmospheres.) The blower flow rate approaches zero CFM when the pressure difference is 2 inches, w.c.

As noted above, one important purpose of MUA is to avoid back-drafting
of combustion appliances, which for some appliances occurs above 0.03
inches, w.c.

A second purpose of MUA is to allow the blower to move a good fraction of its rated flow rate. Even with windows wide open and no screens, the pressure difference across the blower will be significant due to: pressure loss across the baffles, pressure loss passing hood transitions, duct turbulence, and exterior cap pressure loss.

With MUA supplied by other means than screenless windows, there will be some further pressure loss moving air through the MUA ducting, possible screening, and in colder climes, past the heat exchanger or heater.

To look at it another way, when the blower is running the pressure loss
will be just that which limits the flow rate to that which the blower's
fan curve shows matches the pressure loss. There is always MUA, and it
always equals the flow rate that the hood can expel air at to the
outside. If this is inadequate for containment of captured effluent by the hood, then the MUA has
to be improved to allow more flow.

The VaH blower fan curves, data from which has been seen on VaH's web site in the past, shows an even more steep decline in performance with pressure loss than comparable Broan blowers. However, VaH's scheme of using a squirrel cage fan as both a blower and a grease vapor expeller eliminates the bafflepressure loss, so VaH can compete so long as the ducting is short and the MUA is adequate.

kas

Would MUA be an issue for a lower CFM like 600?

In some locales 600 CFM is above the threshold for requiring MUA by code. Otherwise, the usual follow-up question is how tight is your house? A modern tight house will have limited leakage and the result will be possible back-drafting and certain reduction of flow rate. In other words, much more information is needed to answer such a question with any confidence in the answer.

As you are the OP and have already presented a plan for a hood with an aperture of about 7 square feet, your hood requires an actual flow rate of about 630 CFM for good performance. This is already above the 600 CFM zero static pressure flow rate value, and even if you skimp on the hood to a smaller aperture, it is likely that you will only achieve in practice 400 CFM with that blower and catch-as-catch-can MUA, which will support only a 4.5-ish square foot aperture with enough velocity for the hotter effluent plumes.

There is really no way for me to disguise the fact that a pro kitchen requires a pro ventilation system to achieve adequate smoke removal performance and tolerable aesthetics (smell as well as looks). By extension, I believe that even a modest kitchen for which low noise, odor, and grease are goals will require a significant ventilation expense. The alternative is to give up trying to capture and contain all the effluent and instead depend on open windows to provide partial effluent removal, not just make up the air removed by the hood.

kas

Thanks for the explanation. I will look into make up air because I probably want at least 650 CFM.

I live in Los Angeles County and we have some pretty strict codes and I'm sure this is addressed there.

Does anyone have a brand recommendation?

I think we had to have MUA for anything in excess of 400 cfm based on the following Seattle code, and I'd be surprised if most major metropolitan areas didn't have something similar:

M1503.4 Makeup air required. Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

As far as brand recommendations, we currently have a 42" Zephyr Monsoon II 1200 CFM insert, but, despite doing as much research as I could beforehand, we don't like it and are planning, unhappily, to bite the bullet and replace it. As mentioned in other threads, I expected it to be loud on high, but I also expected it to hum along quietly on low. "Low," however, is still 450 CFM, and there's a "thank god" sentiment whenever it's finally turned off. The product literature says low is 3.5 sones, which, according to an online conversion chart, is about 50db. Before we bought the insert I downloaded a decibel app to my phone to figure out what 50 db sounded like and it wasn't bad, BUT, when I turn the fan on low and set the phone on the stove top 35 inches below the hood, the decibel app reads 80-82 db. That's uncomfortably loud for us, and you can't hear the Sonos speaker that's 12 feet away set at a pleasant level--or people talking either, for that matter. In short, it sucks a lot of air, but also your sanity.

We've bought a Wolf liner that has a dial rather than pushbutton settings, inline silencer, and Abbaka rooftop fan, but they're sill in the boxes so I can't comment on how they work or sound. I do know where you'll be able to get a good deal on a very slightly used Zephyr though!

Haha! Thx for the info. My appliance rep recommended a Wolf with 1200 CFM and external blower. But since the fan would be mounted right outside the hood vent my contractor said it wouldn't make much difference external vs internal blower.

My MA insert just got installed literally yesterday