Where is the duct located in your kitchen? What are the problems, if any, with your present cooking setup which is what?

While recirculating range hoods are not ideal, they are helpful. The Prestige brand is one of the best of that type according to some owners here.

I"m gutting and renovating.

A 6" duct is embedded in the building, so its physical limits are permanent.

No need to consider recirculating. Miele can put more than 400CFM through a 6" duct and claim it is done quietly too.

There are several brands that are claimed to be okay with a 6" duct. Shop around. Miele is not the only one.

In what area of what room was the original inlet to the ductwork located?

It's in a column in the kitchen.

Could you describe your condo's exhaust a bit more? The very first thing that came to mind is, if you're blowing more air into a common duct than is already being drawn out as it is, are you going to be blowing your fumes into your neighbors' units? I suppose if every line has its own backdraft damper that risk would be "somewhat" alleviated.

I have no idea how condos are set up. Just thoughts off the top of my head. But I have been in some high end, modern NYC buildings where there is decidedly no air forced from the kitchen into the building's ducts. What the building supplies is what you get, 24/7, no more, no less.

The advisory from my condo Board is that the common duct and the building's blowers are so oversized (built in 1982) that any size blower in the apartment will be fine. That's better than being told the opposite, but it's still not clear.

What we all have right now are low-end hood fans with blade motors. Everybody upgrades when they renovate.

Before going back to the building's resident experts, I'd like to figure out what the physical limits to a 6" duct are. My building's experts don't know. They are just people who learn on the fly just like any other owner renovator.

I'd also like to know whether I can find an inline blower or something just as good. VAH, Thermador, Best, Broan, Nutone e.g.

David

In my building every 4 individual apartment ducts are combined into a common duct.
Oversized external blowers take the "mass" from these big common ducts.
I just need to get air over to that common duct; but i have to go through a 6" duct.
The 6" duct cannot be increased in size. Mine runs about 4 feet until it dumps its air in the bigger duct.

Three years ago we put in our bathroom a remote inline ILF fan in an ILFK kit. Nutone Broan.
Love it. It's such a nice little air noise pulling a lot of air. Like taking a deep breath very slowly.
Love the little button shaped hole in the ceiling that we can close when we want to.
http://www.nutone.com/product-detail.asp?ProductID=10476
I called them and asked for a Variable Speed Control for it.

Then I asked about the HLB3 in the kitchen and a Variable Speed Control for it too.
Got that too: VS64 rated for up to 5 Amps; more is better; I could also get a 3 Amp one.

The outstanding question is whether silent/quiet operation is still going to be in the cards
given that the output vent diameter would be reduced from 8" to 6" over a few feet length.
I'm not sure how to determine the increase in noise and the reduction in strength that will
come from installing an 8" inline blower on a 6" duct.

Later I'll get part numbers for filters and cover grills to suit SO's preference,
if we go with this blower.

David

Any chance you can use an inline blower sized for 8'' ducting and just use transitions to hook into the condo's 6'' duct? The Fantech FKD 8XL is rated at 836 cfm at zero inches of pressure. It's a great fan based on my experience with it. Fantech does not have an inline unit sized for 6'' duct. Now obviously you'd not achieve the 836 cfm due to duct resistance, but it would certainly outperform any dedicated 6'' inline unit, not that I know of one offhand.

I get it now: fantech.net is local; fantech.com is in Australia!

Inline Centrifugal Fans working on a 6 inch Duct are FG6x.
The FG6XL, 483 CFM, draws 1.5 Amps.
The FG6 is 303 CFM drawing 0.7 Amps.

They are designed for the duct, and they pull enough air.
I'll keep exploring the accessories and other fans. Looks good.

David

futuro futuro vent hoods also use 6" ducting. Check out their website

Fantech and Nutone-Broan make inline blowers. I haven't found any mention of variable speed controllers on Fantech's web site.
--Other companies make hoods with fans in them. Futuro Futuro, Thermador, Miele, etc.

-david

davidro1: we have fantech with var speed control. Any rheostat will work as long as rated adequately. See link below for Fantech's own controllers (scroll down to "Variable Speed Controllers."

Here is a link that might be useful: Fantech accessories

You want to examine the fan flow versus pressure drop curve to be sure that the fan can operate into higher pressure than it might have to with a larger duct. Broan, for one, publishes such curves on their website. Fantech also publishes the data.

Generally, it is easier to build a fan to blow air against back pressure, than pull the same flow rate from a similarly restrictive duct, so a hood mounted blower should do well in this case (other than noise). However, the fan blades have to be designed for this purpose, which can be inferred from the fan curves.

kas

Yes, I have seen the curves on Broan and Fantech. But I am not yet able to figure out how to transform duct size and distance into an estimated increased air pressure. Although one can then see the estimated air displacement, no information about additional noise generated is provided and might never be.

I am confident I will find an inline blower that works since the the distance is only a few feet and the smallest inline Fantech fan is made for 6" duct to begin with. Also, Fantech sells silencers that can be added to the line before I close the ceilng.

David

I believe that there are some on-line calculators for pressure drop in various configurations of duct shape and size. I don't have time right now to hunt for them. The pressure loss through whatever is used as an outside rain shield will also need to be considered. In any case, the point of the exercise is to determine whether the fan is in the right ballpark, not which seat will be the recipient of a home run.

kas