When we remodeled the kitchen about 8 years ago we installed a Vent-a-Hood over the range top. The hood has a chimney-like spacer with a 12"x12" cross-section that attaches at the ceiling.
It is slightly out of level. Over the 42" length it drops about 3/4". My theory is that the cause is a slight unevenness in the plaster ceiling, either due to sag in the joists or thickness variation in the plaster. Note that a difference of only 0.2 " over 12" will cause 3/4" difference over the 42" length.
Several years ago, I talked the the contractor who installed it. He proposed to carefully jack the ceiling up from below, then go into the attic and nail in a 2x4 vertical brace from the joists between which the hood is mounted and a cross-piece between two rafters above. For reasons I can't quite remember I decided against that.
Now, I'm thinking about essentially the same idea, but implemented differently. I'm thinking about attaching a length of fairly heavy chain by means of lag screws to the joists, and another length to a cross brace between the rafters above. Between the two chains I will put a turnbuckle. Cinching up on the turnbuckle at the low end should lift the joist just enough to level the hood.
Any opinions on the idea?
TIA
Ed