Natural Gas EXCEL 1.6 GPM VENTFREE (LOW PRESSURE STARTUP) INDOOR TANKLESS GAS WATER HEATER PURE COPPER HEAT EXCHANGER NATURAL GAS LIFETIME WARRANTY on Pure Copper Heat Exchanger Exclusive - Vent-Free Technology No expensive Flue required , for use INDOORS Compact size: front 11.5 - depth 6  height 16 LOW PRESSURE STARTUP - STARTS WITH ONLY 2PSI