Not all 90-degree turns are equal. They can be long and sweeping, or abrupt. They can have internal guidance vanes to redirect flow efficiently. In all of these cases there is some different length of straight ducting that has equivalent pressure loss. Normally, one needs a blower map (pressure loss vs flow rate) and calculations of the same for the configuration of the ducting and losses through the hood in order to determine what the resulting flow will be and whether a larger blower is required for your purpose. This would require some research if you wanted to analyze it yourself. At the higher end, the hood manufacturer may be willing to do this for you. kas

Ah! you missed one of the versions of a comment I have added to quite a few threads. Here it is again. Because we do not get to close off parts of the hood not receiving cooking plume impact, all of the hood has to flow the amount needed at the most stressing part of the effluent plume to be contained at the hood baffle space. How much do we need? Well the actual issue is what velocity of air has to be pulled past the baffles to ensure that the rising plume is pulled into the baffles and contained, versus reflecting off of the baffles and potentially curling back into the room, thereby escaping the capture area and hence removal by the hood. Hot cooking plumes over gas burners can rise at velocities of 1.2 m/s, or almost 4 ft/s. The baffle gap is roughly half the baffle assembly area, so to entrain the plume flow, it seems that some portion of 4 ft/s or 4 x 60 CFM per sq. ft. of baffle area is needed for good containment. Actually, there is usually space under the baffles larger than the baffles proper, so adequate flow is needed all across the hood capture aperture. I believe that I have about 900 actual CFM at home, pulled through a 10 sq. ft. Wolf Pro Island hood. This is equivalent to 90 ft/s. This works over induction hobs, including searing and wok cooking with a 3500W Cooktek wok hob. As it happens, Greenheck also looked into the requirements for CFM, perhaps like me doubting that 100 CFM per ft. of hood edge had a mathematical connection to the process of cooking plume containment. They have published a range of values, and I have taken the liberty of copying their relevant table below. So take your hood area, multiply by some value you believe in for actual needed flow, then multiply by another factor to account for blower ratings not actually applying to the conditions in which they are used. (Another topic written about here more than a few times.) http://www.greenheck.com/media/pdf/otherinfo/KVSApplDesign_catalog.pdf No one has complained here that aiming for 90 CFM/sq. ft. of hood aperture allowed smoke and steam to escape into the kitchen, so long as the hood overlapped the cooking area by enough to capture the expanding plumes.

I'm assuming you've tried a basic Google search for "pivot hinge" and "90 degrees"? https://www.grainger.com/category/hardware/door-hardware/hinges/pivot-hinges?attrs=Range+of+Motion%7C90+Degrees&filters=attrs If all else fails, consider installing some sort of stop. There are stops you can put on the hinge pins of the hinges themselves, and then you can adjust them to where you want them. If you don't want to risk that the adjustment would shift, you can buy bolts to put on there (one on each side of the hole and then tighten them toward one another) Hinge-pin door stops https://www.homedepot.com/p/Everbilt-Satin-Nickel-Hinge-Pin-Door-Stop-15586/202033981 

are the 45s you are referring to 45s....or 90s adjusted to be 45s? I went to the HVAC supply today and they didnt stock 10" 45s so I grabbed a couple 90s...which can be adjusted to be 45. This will definitely be a more gradual sweeping corner (but take up a lot more space). I think I can do one of these corners (2 90s adjusted to be 45 each forming one big 90 corner) from the vertical duct to the blower, but I wont have enough room to do a big sweeping corner to to the wall vent...ill prob wind up putting a single 90 there right out the wall. I think that will be fine...minimal resistance in the (relatively) longer run from the hood to the blower, and then a tight 90 after the blower but that 90 is the *only* duct between the blower and the sweet open air. I guess when I take a step back, the only reason I am doing this is in hopes that the 90 between the blower and the hood will reduce noise a little (as opposed to having a straight duct between hood and blower). I suppose I have nothing to lose and its only an extra 20 bucks in parts. One other question for anyone who has used the fantech blower....I bought the rubber clamps they sell for either side of it. Does the duct not attach to the blower in a male-female manner (pieces of duct do with one another)? does the rubber gasket clamp onto the blower, and then onto the duct so that the metal from the blower than the metal from the duct do not make contact (thus limiting vibrations being transferred to duct work)? I havent studied the clamps (or the blower) yet but in my mind that would make sense....and if its not setup like that, and there is a male-female screw+tape attachment between the blower and the duct...i dont know what the purpose of those rubber clamps would be :)