Hi,

I can't help you with your choice, because we went with a Prestige hood with an in-line blower and duct silencer. But I installed it myself and perhaps I can provide some advice. You have to use rigid duct and so you will need a good source of duct supplies. HD didn't cut it for me, but I needed 10' duct. I would say you want to find a good Heating Venting Air Conditioning (HVAC) shop. You will then need gloves and a tool for cutting the duct. Any good leather gloves will work, but I'd recommend Mechanix gloves-- I love these gloves. How often can you start a role of tape wearing gloves? Sorry, I got off topic, but those gloves are really great.

In terms of cutting, I'd recommend getting a angle grinder with a metal cutting bit. You can use tin snips, but they require work and in the end, the duct looks like it was chewed by a garbage disposal.

Assembling the duct is mostly straightforward. You want the seams to be in the movement of the air-- you don't want the duct seam to be adding friction to the air. After you connect the duct, you need to seal it. Generic duct tape is a no no- as ironic as it sounds. There is the expensive stuff ($15 a roll that is formulated for heat ducts and code approved), but you should consider using mastic. Mastic is applied with a caulk gun and is terribly messy. Please take off those beautiful Mechanix gloves before you apply and and put on some disposable gloves.

Make sure the duct is supported -- the HVAC store can sell you a roll of metal duct strapping that is predrilled. You just cut what you need and affix it to nearby studs. Let me know if you have questions.

Here is a link that might be useful: Mechanix gloves

Thank you so much, these tips are all so helpful!

And those gloves look pretty cool - and not overly costly for what they seem to be.

Don't forget you need 3 sheet metal screws every connection, that is code requirement, before you do any taping.

That is the hardest part for me, I used self tapping sheet metal screws but didn't work so good, I ended up drilling 1/8" holes first. It's hard to get the drill around the duct in some cases.

Tape selections are very confusing, I finally found a tape that says it's for HVAC use, it wide and works great. I included a link it's sold at home depot.

Personally I didn't have a problem using tin snips, it helps to draw a line offset from the edge you want to cut, then just use the tin snips to follow it precisely. If you don't have one, it's preferred to have "offset" tin snip that would help alot.

Here is a link that might be useful: extreme weather foil tape

In the search you are about to do, you will be looking at squirrel cage (centrifugal) blowers, so that is good. That in itself is not a guarantee it will be good, as some centrifuge motors are noisy too. I'd look at the family of companies operating under Nutone, Broan, Best-by-Broan, Venmar, etc. as your basic reference for powerful and quiet centrifuge blowers.

Duct size is the thing. The bigger the better. You can oversize the duct too, and that is good. Less noise, less resistance, more flow. No question.

Often the lowest speeds of many blowers are quiet and make it enjoyable to turn it on and leave it on. The highest speed may be quiet too, in some models; is this a requirement or not? Many people say that they don't care about noise when the highest speed is on, since it is a situation that requires maximum power and nothing else matters for those minutes.

The more air you blow out the duct, the more makeup air is needed to replace it. Two things determine whether you normally have makeup air coming into the house naturally: your climate (in some climates you normally close windows for many months of the year), and your building's construction (in older houses there are leaks everywhere so air comes in through the electric receptacles in the wall... and this is bad air not good). Do you have a whole house air exchanger, an HRV or ERV?

Your hood's canopy ("sump") should be larger than the 30" it has to cover, and placed low near the cooking. (e.g. 24" above the cook surface).
A.) Avoid cross breezes (positioning panels, obstacles, walls, cabinets, doors around the cooktop,)
B.) Place the sump as close as possible to the cooktop,.
C.) Have a place for smoke to collect inside the sump.
(i.e. not to have the bottom of the vent hood be a flat plane where the filter is at the same level as the bottom edge of the hood).
D.) Plan where makeup air will come from.

In several other forums these topics have been discussed. Compared to what the kitchen forum people say, in the HVAC forum the guys say less CFM is OK. Answering your 1st question is risky since you asked about a "minimum" and this could spark controversy. Do you mean to say minimum for the highest need situation? If so, there is no objective answer. Restaurants need triple the CFM that a residential kitchen needs, just to be operable. To be really safe at home, get a hood fan that shuts down when it sense fire. Then, for the other use of the word "minimum" (lowest speeds): get a variable speed controller.

The rated CFM is not your true CFM once installed since it has to push against resistance (duct corners, and length) and in any case this is not the CFM you will use daily, it is the High level which you will use only very rarely. For regular use you will have a lesser CFM.

HTH!
David

Here is a link that might be useful: Sizing a range hood

Wow David, you are a pro!

We live in the Pacific Northwest so we have windows shut for months out of the year. And our house was built in 98 so it should be well insulated.

How can we tell if we have an HRV - is that ticking thing on the wall about the size of a lightswitch that sticks out an inch or so in the upstairs bathroom and makes occasional clicks and ticking noises and has little sun and moon icons on it? I was told it was for air exchange when we moved in.

So if we have an HRV, does that mean I don't have to worry about the make up air, regardless of how big the ducts are (how much air goes out)? Or do some type of hoods (or all) have some type of mechanism to produce make up air?

Considering I've never had any sort of hood (our OTR microwave isn't even hooked up for the exhaust option), I guess even the smallest CFM amount will be a vast improvement. Quiet and well-functioning are the 2 most important things. I don't mind it being louder for the rarer occasions when I need really high power.