The Ultra Fin system by MacDuffco Inc., uses aluminum fins to heat wood-frame houses. It was designed to simplify existing models of radiant heating. It uses 5/8-inch O.D. composite tubing installed 3 inches below the floor, through joists. Heavy-gauge aluminum fin is attached to the tubing in each joist space using six pop rivets. Uses less than one-third of the tubing required by most radiant systems.