Combustion air is the outside air that gas-fired appliances need to burn fuel safely. Without enough fresh combustion air, fuels burn incompletely, producing carbon monoxide and reducing efficiency.
Modern high-efficiency furnaces use a direct intake from outside (sealed combustion). Older standard-efficiency furnaces draw combustion air from the room where the furnace is installed (open combustion) — which means that room must have adequate ventilation back to the outside.
Why this matters in Colorado
- Altitude requires more air volume per BTU of fuel (thinner air = less oxygen per cubic foot)
- Tightly-sealed modern homes can starve open-combustion furnaces of air
- Building exhaust fans (kitchen, bath, dryer) can backdraft combustion gases into the home
- Common in basements that were finished without addressing combustion air
A Common Renovation Oversight
Finishing a basement or converting a utility room without addressing combustion air requirements creates a CO risk. If you’re planning a basement remodel and you have an open-combustion furnace or water heater, get combustion air evaluated before construction.
Related: Furnace, Carbon Monoxide, Heat Exchanger.
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Right Way Mechanical is a family-owned HVAC contractor serving Wheat Ridge, Arvada, west Denver, and the Colorado foothills.