DWHR double-walled heat exchangers meet the Uniform Plumbing Code, Section 603.3.4; 1995 CABO (Council of American Building Officials) One and Two Family Dwelling Code, Section 3402.3.1; 1998 ICC (International Code Council) One and Two Family Dwelling Code, Section 3402.4.2.1; and the 2000 and 2003 ICC International Residential Code, Section P2902.4.2 – Heat Exchangers.