Gas Water Heaters with Tank

Estimate peak-hour hot water demand across all fixtures likely to draw simultaneously, then compare against the unit's First Hour Rating (FHR), which accounts for both tank capacity and recovery rate together. Tank capacity alone can be misleading — a smaller tank with a higher BTU input can outperform a larger tank with a slow recovery rate.

Atmospheric units rely on natural draft rising through a vertical flue and draw combustion air from the surrounding room. Power-vent units use an integral blower to push exhaust through smaller-diameter pipe, often horizontally, giving more venting flexibility. Direct-vent units draw combustion air from outside through a sealed intake, which improves safety and efficiency in tightly sealed mechanical rooms.

Only with a manufacturer-approved conversion kit that changes the burner orifices and adjusts the gas valve regulator — natural gas and propane burn at different pressures and BTU content, and running the wrong fuel without conversion is a safety hazard. Many manufacturers offer dual-rated units or approved kits; check the rating plate and installation manual before attempting a conversion.

Check the sacrificial anode rod every 2-3 years, sooner in areas with aggressive or softened water — once it's consumed down to the steel core wire, the tank itself begins corroding instead, which is the leading cause of tank failure. A rod showing more than 6 inches of exposed core wire should be replaced.

Requirements vary by jurisdiction and by unit type (atmospheric vs. power/direct-vent), covering vent pipe diameter, slope, termination clearances from windows and air intakes, and combustion air supply to the space. Always follow the manufacturer's installation manual and local plumbing/mechanical code — venting is one of the most commonly cited issues in gas water heater inspections.