We have taken up an old hardwood floor and are about to have carpet installed. The old, rough planks are exposed, there is an extremely heavy radiator along one wall and one end of the brick hearth is about 1/4 inch higher than the other. Do we need to put down a layer of plywood? Is there an easier option? Can Floor Leveler be used on a small area such as a hearth so that tile can be laid over top? Can this be done by New Year's Eve. Thanks.