First of all, grease is filtered out, not vented out.

If your duct runs straight up without any turn, I won't call 15' "long distance." A 600 cfm blower should have > 500 cfm left even if you use 6" dia. duct. (Not that I recommend 6".)

Actually, the grease effluent exists as as a wide spectrum of particle diameters, only the larger of which are (mostly) filtered by residential systems. Even elaborate multistage filtering that is possible with some commercial setups can only filter a portion of the particle size spectrum. To my knowledge, the only near perfect grease collection systems use intense UV to break the grease molecular bonds.

If designed correctly, the venting system will vent most of the smaller particles not caught by the filter to the outside. This requires the air velocity in the ducting to be high enough (around 1000 fpm) that the mid-size particles tend to not condense on the duct walls.

kas

you turn it on top speed for 20 to 40 seconds.
This gets an air current flowing.
Then you lower the speed to level 2 or 1.
This is how you overcome the inertia of the air initially.

Kaseki,

You are absolutely right. I should have said grease is MOSTLY filtered out ...

The OP seems to worry about whether a mid-range blower is capable of "carrying grease" through a 15' vertical pipe. Personally, I wouldn't worry too much about that.

What if there is an elbow?

Thank you for the responses! It sounds like we should be fine, yes? Dapitou, forgive my ignorance but am I correct in assuming that the vent pipe should be greater than 6"? And I'd forgotten that "real" vents filter out at least a good portion of the grease. What I have now doesn't do anything but make noise (and microwave food of course).
Davidro1, your idea of turning the fan on "high" initially makes sense - thanks!
So - who does one hire to install the vent pipe? An HVAC contractor, since the "V" stands for Ventilation? Or would that be included in the installation of the vent hood, if we go with a separate vent hood and microwave instead of a microhood?
This forum is an amazing source of information and I sincerely appreciate the assistance!

Yes, the bigger the pipe, the better. Suppose 8" pipe is used. A 45-degree elbow = 3' and a 90-degree pipe = 6'. I copy those numbers from the planning guide that came with my hood. Different manufacturers may have different numbers.

In our older home, we had a hood rated at 600 cfm. The duct goes up 3' to the ceiling, makes a 90-degree turn, and then travels between joists for 18' to the exterior wall. That's equivalent to 27'. According to the planning guide I have, it should lose about 100 cfm. It's a little underpowered for us but not too bad and I mainly do wok cooking on 15000 btu burners. The hood does have a good capture area, which is important. So dear ReginaLiz, a microhood won't work!

In our older, older home, we hired a handyman to install the hood. But not any handyman though. The guy needs to be a licensed electrician since there is some electric work involved. Hope this helps.

LOL, from the post title, I wondered if you were posting your frustrations from Siberia.... :-P

Instead of a round duct of X inches diameter, you can use one size greater diameter.
Also, a round duct can be transitioned into a rectangular duct. This is good when one dimension has to remain less than a specific small number in order to fit a space.

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What if an elbow?
No big deal. Not at all.
An elbow = an obstruction, easy to calculate.
An elbow is the equivalent of a few more feet of straight duct.
It's not anything harder to understand or to work around.

=

Thank you all again for the additional information - I'm starting to get more comfortable with this. Dapitau, I've accepted that I will have to sacrifice some of my very limited counter space for a microwave but it's for the greater good. Davidro1, good to know that we can modify the duct to rectangular, as our route to the roof is limited. Finally, Cj47, thanks for the chuckle! Fortunately I'm not *that* frustrated - yet - and we're nowhere near Siberia; we're actually in Texas and it was in the 80's again today.

I would be looking for something in the 700-900 cfm range. Reason being, at high speeds the hood will be noisy. Getting an oversized unit means you can run it at a lower speed.

As for installing it, it depends. It doesn't sound that difficult from your description, so I think an HVAC guy would not be interested. A general construction type (handyman) could probably do it without too much effort. Since you're replaceing a OTR microwave, the electrical would be no more difficult that a disposal or dishwasher.

Sharp makes an over-the-counter microwave oven that would use cabinet space instead of counter space, if counter space were more important.

kas

Combination microwave/range hoods rarely exceed 300cfm - some do 400cfm but you'll need a separate exhaust fan for seriously long duct runs, especially if there are several bends in the ducting.