It really depends on how tight your house is. 1200 CFMs will suck a lot of air and if the house is tight you run the risk of backdrafting your furnace. Generally with anything over 600 CFM you need makeup air and places like MN require makeup air with anything over 300 CFM. Personally, since you don't have a grill, I think you would be fine with 600 CFM - others on this forum will disagree with me, but I think manufacturers and salesmen oversell hood requirements.

Thank you weissman, but I already have the 1200cfm motor mounted on my roof, so I gotta use it. If I did need makeup air, would it be cheaper to just kick it down a notch with a 900 cfm unit? I guess I'm trying to figure out what would be cheaper and better, a smaller motor or makeup air? I wish I had found this website BEFORE I made all my purchases. And how will I know if it's backdrafting my furnace, which is downstairs from the kitchen?

Changing the motor might be cheaper than putting in makeup air but there are different kinds of systems I think - active and passive and ones, with and without heaters. I'm not an expert - others on this forum can probably advise you better - but you'd probably need someone like an HVAC expert to give you an estimate. For now, I'd just open a window if you use your hood on high.

If you don't get any responses - repost with a more descriptive title that includes the words make-up air.

I would do a search of MAKE UP AIR or MAKE-UP AIR on this forum and on the Kitchen forum. You maight find some more useful info.

Where are you located? How many fire places do you have?

Hi guadalupe, I'm located in Southern New York State. WE have one fireplace.

Haus, I did the search, and now I'm finding that people are have problems with Wolf AG ranges....Yikes, I have one of those too......Oh NOOOOOO have I opened a can of worms?

1200 cfm is a lot but I still think your problem would likely be handled nicely by simply having a variable-speed control. In warmer weather with doors or windows open there would be no problem. In colder weather, when the house is closed up, keep the power down. How much would depend on how "tight" house is when closed.

My place is 3000 sq. feet. My 600 cfm blower (sucker?) will, indeed, draw from the fireplace when everything is shut up so can be troublesome in the winter. In warmer weather a single open window solves the problem.

If you you want "perfection", install make-up air source. For many situations I think its overkill. I like the option of full-blast when conditions allow it.

it is not necessary to operate any hood at high speed, low is more than adequate unless you made a mistake and are burning food or creating smoke with frying, woking or grilling. It is more important to operate the hood if you are using the gas oven, if it is an electric oven it makes no difference. Gas ovens have high output burners and need air for better temperature and to handle the oven pollution. Operating the hood on low will reduce the cfm and lessen your need for any make up air.

I'm a little late to this discussion, but isn't it pretty straightforward that instead of replacing the entire blower, you just turn your down? There is nothing that would require you to run the 1200 cfm blower full blast all the time, and if you run it slower, then it will be no more of a problem than if you mounted a smaller blower.

That's particularly easy if you have an infinitely variable speed control, but otherwise, just run at "low" or "medium" instead of "high."

This is a recurring debate and weissman and I tend to be on opposite sides. My take is that, as long as code does not require it, you are not in an extremely "tightly" built house, and assuming that you live somewhere reasonably temperate where at worst during the winter you could crack a window if you were searing, grilling, etc, then makeup air is not required. I know my HVAC contractor and hood supplier are both comfortable with our lack of makeup air with our 1200 cfm blower, but we're in Georgia with a house that is far from tight.

You have to take it all into perspective and determine if your make up air requirement, if any at all, is active or passive. Of course, even if not required by code, then you should assess need.

Active is forced back into the dwelling and, as others have pointed out, some codes are so restrictive as to require the air to be heated and/or cooled. Passive, as I have coined it, is merely a source from which the unit can pull from.

I never considered that codes might require an active source especially in residential but have learned very differently listening to others here.

I do not know whether my area requires make up air but it never came up, even during inspection. Because of the CFMs I put in this house, I inquired about the advisability of a fresh air source and was told it was called replacement air and that I should consider it since I was putting in 2500 CFMs. So, I had a vent to the outside put in to provide a source for the unit to pull from, similar to the fresh air requirements for most fireplaces (and which is code for my area). It vents directly under the range and to theoutside. Until that vent was active, I cracked a window when venting above about 1/3 speed. The fresh air source and, before hooked up, the cracked window worked fine. I discussed the issue with the distributor and an architect both of whom agreed I needed make up air but both of whom agreed my passive system/source was fine. The architect was very familiar with the active forced systems especially in a commercial setting and felt that active systems in a residential setting were overkill. As an aside, I believe all modern furnaces are required to have their own dedicated fresh air source which should mitigate most if any backdraft risk from a vent hood.

In our last house which was new contruction and very tight, we had a 900 CFM hood and had never heard of make up air nor was it ever a problem.

I say keep what you have and, at most, put in a fresh air source...or crack the occasional window if necessary.

As usual breezy makes good points. In particular he distinguishes active vs passive makeup air and also addresses in passing the issue of heated/cooled air.

In my mind, the difference between passive makeup air and opening a window is quite small. The main advantage I can see to "formal" makeup air is that the airflow is directed into an enclosed area, avoiding drafts of cold or hot air. Otherwise both options work equally well in preventing backdrafting etc.

With the window approach, as long as the temperatures are not extreme, a decent HVAC system should be able to compensate nicely for the flow of hot/cold air in through the window. The makeup air system does have the advantage of not relying on the operator remembering to open the window.

Really the only setting where I think makeup air has a clear advantage is if you go to the expense and complexity of installing a heat exchanger. This allows some of the heat of the air being exhausted (in winter) to be used to heat the incoming fresh air, thus reducing the lost energy from pumping heated air outside. That is an appealing idea, but the expense is significant for the amount of time we spend with the hood going full blast. So, we're going with the open window.

Thank you all, yes I will probably run it at lower speeds most of the time. But my concern was if I do need to run it at high, am I in danger of harming my family. And if it's sucking all the fresh air out of the house how will I know? I'm probably being more concerned about this than I need to be, but it seems that this whole kitchen renovation process has made me a nervous wreck. Can you tell that I can't wait until it's all over with?

josie, RELAX! take a deep breath (unless you have your hood on high:)). You should be fine. There is little risk you are going to deplete your house of all fresh air.

clinresga - sorry, I did not mean to make a real distinction b/t the cracked window or my set up except that maybe the proximity of my replacement air vent is closer by a few feet (at most). I cannot really tell the difference b/t the cracked window or the vent system.

breezy: no, that's exactly how I read you. I agree that there is no real practical difference, just a bit less hassle if the venting is there all the time instead of having to open the window. I certainly agree with the others that the OP is worrying too much about this--she should do fine.