Heatco ensures INNOVATION, QUALITY, RELIABILITY in all of our products. HDA OEM Insert Provides 80% efficient gas heat ranging from 150,000-600,000 BTUH input HDB OEM Insert Provides 80% efficient gas heat ranging from 180,000-600,000 BTUH input HDG OEM Insert Provides 80% efficient gas heat ranging from 050,000-400,000 BTUHinput