"What's the difference between flue type gas water heater and exhaust type gas water heater?"

"What's the difference between flue type gas water heater and exhaust type gas water heater?"

Summary

Flue-type gas water heaters rely on natural convection exhaust and require a dedicated chimney; exhaust-type uses mechanical exhaust, providing safer and more efficient combustion and installation flexibility.

Compared with the direct gas emission of flueless gas water heater, flue type emits gas to the outside through smoke vent, which solves the problem of indoor air pollution to some extent, and it is a remarkable progress in technical safety for gas water heater.
The primary difference between a flue type (often referred to as natural draft) and an exhaust type (forced draft or power-vented) gas water heater lies in how they vent combustion byproducts and manage airflow. We can see below structured breakdown:
 Ⅰ. Venting Mechanism
- Flue Type (Natural Draft):
- Relies on natural convection (hot gases rising) to vent exhaust through a vertical flue or chimney.
- Requires a dedicated vertical pipe or existing chimney for proper draft.
- Susceptible to back drafting if airflow is disrupted (e.g., negative indoor pressure, blocked flue).
- Exhaust Type (Forced Draft):
- Uses a fan or blower to mechanically expel exhaust, allowing flexible venting (horizontal or vertical).
- Less dependent on natural airflow, reducing backdraft risks.
- Often called "power-vented" or "forced exhaust" (FF type in some regions).
Ⅱ. Air Intake
- Flue Type: Typically draws combustion air from the surrounding room (open combustion), requiring adequate indoor ventilation.
- Exhaust Type: May still use room air for combustion but can be paired with sealed systems (balanced flue) that draw outdoor air for safer operation.
Ⅲ. Installation Flexibility
- Flue Type: Needs proximity to a chimney or vertical flue, limiting placement options.
- Exhaust Type: Can be installed farther from chimneys, with vents routed through walls or roofs, offering greater flexibility.
Ⅳ. Safety & Efficiency
- Flue Type: Higher risk of carbon monoxide leaks if venting is compromised. Efficiency may vary with draft conditions.
- Exhaust Type: Safer due to active venting; often more efficient combustion due to controlled airflow. Consumes electricity to run the fan.
Ⅴ. Regional Terminology
- "Balanced flue" systems (sealed combustion) are a separate category, drawing outdoor air and venting exhaust via coaxial pipes. "Balanced flue" systems is more safer.