Effectiveness is influenced by capacity of unit. If you are trying to mount a 270 cfm fan more than 30" above cooktop, then it may make noise but will do little to clear the air. If it is 1000 cfm, then it can be higher than 30". So the answer is "it depends". Most people don't mount them more than 36" above the cooktop unless it is a really high powered unit.

With white fixtures, keep your floors and all tile white or a stone that is mostly white. You can paint the walls above the wainscot (which might be glossy painted wood or beadboard, or you might employ a cabinet for the sink that was painted a very soft sky blue. One narrow trim piece of tile running through the white tile might be the same tone of sky blue. Then, add blue linens / towels / etc. [houzz=] Now, consider what other colors are in your home and select one that is clear and soft and lovely with white. You might use that color instead of sky blue. I used sky blue because it is the color of water and therefore always appropriate in the bath, but you can make the bath flow with the colors you have or plan to have in your home. If this was a master bathroom instead of a common or guest bath, I would shift the choices of stone and tile from white plus white to a lovely off-white, cream, or almond tone - like travertine. Use a neutral like chocolate on the cabinet and add color only with linens and perhaps some art on the wall. [houzz=]

Thnks a lot gor taking your time from aura interiors.i admired your work been a follower too....im waiting till my kitchen slab is fixed in black granite galaxy.... My idea right now something young and luxurious looking which black n metallic will give... Any suggestions regarding toughed glass for kitchen is it durable... Houzz has so much to offer...great help... Thnks again

Thanks for both of your responses CUBSpaces team and Shweta from Shades studio. It really gives a clarity about possible consequences. I am now doubt free about changing whole things in Bathroom as it will be interconnected. However will appreciate your opinion on few things: 1. Kitchen wall tiles: I have those from countertop height to roof(almost area of 6X15 feet) which are good and not hollow. I changed countertop 5 years back without any damage to these tiles. It might cost me another 10-15 K, but I feel the whole process and quantity of wasting old good tiles makes me little sad. 2. kitchen countertop: Made new around 5 years back. I don't expect to get it all intact. But large pieces can be cut and can be used as top for other freestanding structures like dishwasher, front load washer, heighten base cabinets, etc. 3. Plywood: I don't mind giving enough labour charges for old sheets recycle. I am planning to use doors, loose sheets(like kept on bed frame of settee frame.) or parts of big frames like settee. I am keen on reducing waste than to save money. You can see various DIY ideas by western people, who remove or sand laminates and re-paint furniture, or carefully remove hollow tiles and re-attach them. Some are also re-painting ceramic tiles. I am just asking myself: Are we creating more and more waste by use and throw approach every 10-15 years, just because we can afford it?