Use the slab-heating manual and the intended finished floor assembly.
The WarmlyYours Slab Heating installation manual distinguishes bare concrete from slabs with a floor covering:
- For normal bare, stained or stamped concrete, its cable instructions specify 3-inch spacing.
- Where the slab will have a covering such as tile or wood, its cable instructions specify 5-inch spacing for a maximum of 15 W/sq. ft.
- The listed Slab Heating mats are rated 20 W/sq. ft.; that does not make them interchangeable with a cable layout intended for a covered floor.
Use the product’s approved layout and the finished-floor manufacturer’s temperature limits. Have the installer check the locally adopted electrical code and product listing.
The old article’s 33 W/sq. ft. and 16.5 W/linear-ft figures and NEC section numbers should not be used as universal current limits. Cable, panel and floor-covering provisions depend on the equipment and code edition. The 15 W/sq. ft. instruction above is specifically the manufacturer’s published covered-slab guidance.
Source: Slab Heating installation manual (installation requirements, mat table and Appendices C/D).
