Your best bet is a CKD kitchen designer. A good one will know this stuff cold. If you get a professional range, you need more ventilation. However, depending on where you live, you could need make-up air, which is costly.

A kitchen designer can help you balance your cooking needs, your space, your budget, etc.

A person at an appliance store is a salesman. The one you visited with was doing his job (“we will order it for you.”)

They’re not HVAC contractors. You are expecting too much. And you are expecting spoonfeeding for free too boot. You need to take the bull by the horns, and do your research - there’s a ton of info on this forum. I doubt that the appliance salesperson has as much info in his/her head as what you can learn on this forum.

Things you need to know:

- what your existing duct size is that goes from the hood to the outside. Since it’s set up for a microhood, it is likely 6” diameter or smaller. It needs to be 8” or 10”.

- learn all you can about MUA, and be prepared to spend money on it. Alternatively, forego MUA but then you must keep the exhaust’s cfms under 400.

- determine what size hood you can fit. Ideally it should be 6” wider than your cooktop, and 24” deep, but you may have budget constraints so figure that out.

- start researching brands and the sizes offered given your budget. Look for hoods with baffle filters.

Salespeople don't always have product knowledge.

You can post your questions here, in Kitchens, and there are some REALLY knowledgeable people to help you. That's what I'd do.

I understand all of that. I'm replacing a 30" 4-burner gas range with another 30" (4 or 5 burner) gas range, so I would think the answer would be something like "you need at least X CFM for that, and anything over Y would be overkill - and if you have over 450 CFM, you need makeup air" (which I already knew from local codes).

I'm not opposed to hiring a kitchen designer, but it seems like it might be overkill for a design that is essentially an update of an existing layout...and I'm not clear on how they're compensated (flat fee, percentage of purchases, project budget, etc). I've already got my contractor, who I've worked with for 17 years on this specific house, so he knows it pretty well.

It sounds like you already know what you need to know:

• Size - 36"W x 24"D (for 30"W range)
• Exhaust - no more then 450 CFMs if you aren't planning/willing to do make-up air

Now you need to determine the size duct you have. If you need a wider one, can you replace the existing with the correct size? Only you or your Contractor can determine that.

See Shannon's post above.

"And you are expecting spoonfeeding for free too boot."

Not really - I'm trying to find out as much as I can about the issues I'll need to solve in the project, including research on here. If it takes paying for a kitchen designer to size the hood, I'll pay for that. I'm happy to do as much legwork (or Google, or calculations) as it takes. If I were selling appliances, and a customer asked me something that I couldn't help them with, I'd try to point them in the right direction ("I can help you by.....referring you to this HVAC guy, setting up a consultation, or putting you in touch with a kitchen designer")

I'm happy to pay for advice, whether it's contracted advice or built into purchase. I was just a little put off with the 'tell us what you want and we'll order it'. I can do that online.

Suppose you recently married a Chinese lady who likes to cook with a wok, and you're buying her a professional, high BTU 30" range with wok burner. That will require different ventilation than if you're wanting to simmer spaghetti sauce all day. We don't know how you cook, and neither does that appliance salesman.

I got lucky. I bought a 30" 5-burner Bosch gas range and 30" 600 cfm Bosch vent fan. My kichen designer thought about the MUA, but knew I wouldn't run it full blast and knew the electrical, plumbing and gas inspectors in our city wouldn't care.

My kitchen designer and I discussed all the microwave possibilities. We settled on a small countertop unit, which I got rid of because I never used it.

It's possible that it was the hood guru's day off.

Many years ago, we did a down-to-the-studs kitchen remodel. When the Thermador downdraft died, we knew we wanted to replace it with real hood (and an all-gas no electronics range) So we went to the local 90 years in business appliance place, and talked to their hood guru. We explained what we were doing, the range we wanted to buy, and walked out with a suitable object. I honestly don't know exactly what the suitable object is, in fact, but it is suitable. So I don't think your expectations are unreasonable. Of course that was pre-supply chain anything.

Thanks for all the comments so far, even the ones that are exasperated by my approach. I'm just trying to get educated before laying out a significant amount of $ (even if I need to spend part of that budget getting educated).

I've seen the calculator that Shannon_WI pointed out, and it mainly comes down to 1) How big is the kitchen (to determine # of air exchanges) and 2) How many BTUs does the range put out?

The range location in this case is ideal - it's on an outside wall, and can vent directly out, so no worrying about turns or small in-the-wall vents. We can go as large as we need. The kitchen 'size' is 11X13, but it's open to a 10X13 breakfast nook, and right next to an open family room with a vaulted ceiling. So, is the kitchen volume just the 'kitchen' part, or does it include one or both of the other rooms?

For the BTUs, it's going to be somewhere between 40K (current) to 60K (pro-level 30") range. If running all the burners at once, that could need 400-600K CFM, but I've never ran more than 2 at the same time. I know that today, the microwave/range hood, which SAYS it has 400CFM max, sets off the smoke alarm every time I use the broiler, generate ANY smoke, or just heat up a pizza.

Because the microwave only projects about 13" from the wall, and may be overly generous about the CFM rating, I may be able to solve this with any decent dedicated range hood that does 400+CFM. I just don't like using the smoke alarm as a timer. When it goes off, the food's already 'done'.

One more thing: your gas line if you're on natural gas. I would have a kick-ass professional range, were it not that I converted from an electric range to gas, and the existing line, after accounting for our gas furnace and fireplace, only had enough BTUs left for a domestic range.

You may want to explore the induction range options. Induction requires less ventilation. No waste heat to deal with. And there are other positives. Much info on this site.

I’m with Dan. Most folks these days are looking to get rid of gas ranges and go to induction which is cleaner, safer, and requires less ventiation. You will find a wide array of basic hoods that can pull the very limited heat and effluent of an induction range. Good luck.

There are appliance stores and then there are appliance stores. Some are very good at having nice displays and ordering what you want. Others have knowledgeable staff. You may need to go to the high end store. But go to a different store. Or two more different stores.

I've read some of the advantages of induction cooking, but I'm likely to stay with gas, which is still still seen as more desirable in this part of the country (DC Metro area).

There's a home improvement show coming up at the end of January - I'll see what questions I can get answered prior to that, so I can be well-informed before the show. I'll be buying appliances from somewhere, we'll see how that works out.

I happen to like gas but the easy way to figure out the hood is to read the info from the maker of the range you are buying. I agree you need a KD who can help with all the needs and wants . A salesperson is exactly that they seel you what you want.BTW the whole point of the show is they give you advice and you need to get your choices of appliances nailed down

Doesn't the range you want specify the hood size? I have induction so mine was easy.

In the spirit of the season: Holy Mackerel! There are scores, if not hundreds of messages here from just myself describing the method of determining capture area, calculating CFM, duct size, consideration of MUA approaches, minimizing noise, etc. From @clinresga a decade ago to @opaone in recent years, along with others, many have joined in this pursuit of performance adequacy/excellence. I can't believe that any significant hood research was performed reading threads here, much less checking out the various references scattered about within them.

Before I started my kitchen reno in 2008, I spent the last 5 months of 2007 reading most threads on the Kitchen and Appliance forums for background, and then researching kitchen ventilation -- the least well understood by the forum members -- by downloading and reading the many on-line papers on the subject. Some effort really means a lot of effort. You have to live with your choice, and it has to balance cost, aesthetics, and most importantly from my point of view -- performance. That means, at a minimum, knowing what performance means in the context of kitchen ventilation.

Let me know what I failed to adequately explain and I will be happy to expand on the subject.

This is why you need the KD. You want handholding and being walked through the multiple interactive Venn diagrams thst encompass the bariations of options. Plus, you need a lot of advice on your makeover too. Get yourself up to an appointment at Jennifer Gilmer’s showroom. Then pay them a design retainer to coordinate and hand hold.

@David Hollingsworth - Take the offer above, @kaseki has forgotten more about kitchen ventilation than most will ever know....

Thanks for all the input, and I may take @kaseki up on that offer. I've gotten in touch with an experienced / recommended kitchen designer who should be able to help me navigate things as well. From what I'm seeing, I'm likely over-complicating things - I'm not putting in a 48" Blue Star or Viking, it's going to be a 30" 4-5 burner range - but I want to solve my current kitchen complaint, which is that my GE gas range and microhood setup sets off the smoke alarm if I look at it sideways.

Several times in this thread the duct that you have in place has been mentioned. You have not responded. This is crucial information you will need for your purchase. If the duct was sized just for your OTR microwave, and you will not be changing the duct, then your hood choices will be limited to those hoods that are spec'd to work with the size duct you have. If you are able to change your duct, your options are much better.

People frequently say on this forum that induction cooking needs fewer cfms. Despite being corrected by people like Kaseki and others, this thinking persists. The reality is that if you are cooking something that gives off a good amount of effluent (i.e. smoke and grease spray) such as bacon or steak, you will need the same cfms to exhaust that effluent regardless of whether the cooktop is an induction or gas one.

Sorry, I thought i had posted this earlier:

"The range location in this case is ideal - it's on an outside wall, and can vent directly out,"

The exterior vent is connected to the microwave, so it's just the thickness of the wall. There is currently a 10" rectangular exterior vent that we would replace with the new duct/vent. So, we don't have any real existing ductwork to contend with, and we can size as large as we need for the range hood.

I don’t think you are asking too much. I always ask for recs at my local appliance store and always get solid recommendations, once they know what I’m looking for. You can read hundreds of reviews online, but that ends up being mind numbing —I much prefer getting a rec from someone who knows the products people like in the area, as well as which products they get complaints about.