My entire house have porcelain tiles. I would like to install hardwood over all area except the bathroom and kitchen. Can I install hardwood over the tiles without remove tiles? Some contractors told me I have to remove it. Some told me I can use specialty glue to glue hardwood to tiles. Who would be right?

Frankly you CAN go over the tile but I predict you will not be as happy with the results.

I've seen it work on one occasion but it was a "floating" floor... interlocking hardwood (possibly laminate) over a pad - the same pad they use under laminate flooring.

It just was not as level or solid as installing over good plywood.

Yes this can be done make sure tile is clean and use a good glue like bostiks best.this is not recommended because of tile height differences and if tiles start popping loose it is a nightmare to fix I have done this personally and recommended that they take up old tile but this is what the customer wanted, the floor looked great afterwards and still does no call backs after 3 years except to do more work. Good luck

A full hardwood floor is nailed to a sub floor. The comment regarding gluing is more appropriate for a engineered wood floor or thick laminate. The height difference between the old tile and the surface of the hardwood would be quite significant and become a trip hazard. Even ripping out the tile might not expose a nailing sub floor. Do you know for sure what is under the tile?

The tiles were on the slab foundation so I guess I could put the engineered wood over the tiles with glue.

Thanks

Remember to clean the floor well and spend the extra money on a good adhesive

Shop around and check installation directions from several manufacturers, most laminates are a floating floor on a foam layer and do not get glued. The same is true for many engineered lumber floors.