How It Works – Step-by-Step

 1. Gas Combustion Begins

• Natural gas or propane enters the burner.

• Combustion occurs in a sealed chamber, producing hot gases primarily composed of:

  • Carbon dioxide (CO₂)

  • Water vapor (H₂O)

  • Heat (thermal energy)

 2. Primary Heat Exchange

• Hot gases flow through the primary heat exchanger.

• Water circulating through this exchanger absorbs most of the sensible heat.

 3. Condensing Stage (Secondary Heat Exchange)

• Before exhaust gases are vented:

  • They pass through a second heat exchanger (usually made of stainless steel).

  • Water vapor in the gas cools and condenses into liquid form.

• As it condenses, it releases latent heat of vaporization (~970 BTU/lb), which is absorbed by the incoming cold water.

  This step is what makes condensing systems significantly more efficient.

4. Condensate Management

• The condensed water (a mildly acidic liquid, pH 3–5) is collected and drained.

• Often, a neutralizer kit is used to raise the pH before disposal.

 5. Low-Temperature Exhaust

• Exhaust gases, now much cooler (~100–140°F or 38–60°C), are vented through PVC or CPVC plastic pipes instead of metal flues.

• This reduces installation costs and increases safety.

Thermodynamic Concepts

Performance & Efficiency

• Thermal Efficiency: Typically 90%–98%, depending on usage and system design.

• Uniform Energy Factor (UEF):

  • Traditional gas heaters: UEF 0.60–0.70

  • Condensing heaters: UEF 0.90–0.98

• Energy Savings: Can reduce gas bills by 20–30% compared to standard gas units.

Design Variants

1. Condensing Tank Water Heater

   • Similar to standard tank models but with condensing exhaust handling.

   • May have larger secondary heat exchangers.

   • Good for households with consistent hot water demand.

2. Condensing Tankless Water Heater

   • On-demand heating.

   • Very compact, highly efficient.

   • Ideal for space-saving and endless hot water.

Maintenance Requirements