MacDuffco's Ultra-Fin is a hydronic radiant heating system designed specifically for wood-frame housing. The Ultra-Fin system uses 1/2" tubing to circulate hot water throughout the underfloor joist spaces, where heat from the tubing is conducted to attached aluminum fins. The fins transfer the heat and warm the air in the joist spaces, creating hot air convection. The heated air warms the floor uniformly. MacDuffco Inc.