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Furnaces

Residential gas heating furnaces are commonly categorized by how they burn fuel, move exhaust gases, and control heat output. Below is a clear overview of the main types you’ll see in homes.

Gas Furnace


1. Natural Draft Furnaces

These are the oldest and simplest type of gas furnace.

  • How they work: Hot exhaust gases naturally rise and exit through a chimney (no exhaust fan).

  • Efficiency: Low (typically around 60–70% AFUE).

  • Pros: Simple design, fewer mechanical parts.

  • Cons: Higher energy waste, less safe and less efficient than modern options.

  • Where found: Mostly in older homes; rarely installed today.

2. Induced Draft (Non-Condensing) Furnaces

A more modern and common design.

  • How they work: A small fan (inducer motor) pulls combustion gases through the heat exchanger and vents them outside.

  • Efficiency: Medium (about 80% AFUE).

  • Pros: More efficient and safer than natural draft furnaces.

  • Cons: Still loses some heat through exhaust.

  • Where found: Many homes built from the 1980s to early 2000s.

3. Condensing Furnaces

The most efficient type of residential gas furnace.

  • How they work: Capture extra heat from exhaust gases by condensing water vapor, extracting more usable heat.

  • Efficiency: High (90–98%+ AFUE).

  • Pros: Lowest energy use, lower heating bills, environmentally friendly.

  • Cons: Higher upfront cost; requires a drain for condensate.

  • Where found: Most new home installations and energy-efficient upgrades.

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