An unlisted water heater is being installed in a combustible-framed alcove. What is the minimum required clearance on all sides and rear, and what must be done to the floor?

• 12 inches on all sides and rear; the combustible floor must be protected in an approved manner.
• Clearance per manufacturer's instructions; floor must be concrete.
• 6 inches on all sides and rear; floor protection is not required.
• 12 inches on the sides and rear, 18 inches in front; floor protection is not required.