How long does the floor take to heat up?

This will vary depending on the construction of the sub floor. For example, uninsulated concrete subfloors will take considerably longer than plywood sub floors. Heat-up times will depend on such variables as the thickness of the tiles and the design of the sub-floor however, here are some rough guidelines:

• Concrete with insulated tile-backer board - 3/8": 1 hour
• Un-insulated concrete slab: 2 - 8 hours
• Insulated concrete slab - insulation under screed: 2 - 5 hours