Direct vs Indirect Operating-Cost Estimator

Koven Air Tool 3

Direct vs Indirect Operating-Cost Estimator

Compare annual gas cost of a ~92%-efficient direct-fired unit against a ~80%-efficient indirect unit, using your own numbers.

Illustrative estimate from your inputs and published efficiency figures (~92% direct / ~80% indirect). Actual results vary with load profile, controls, and fuel. Direct-fired introduces combustion products into supply air; indirect keeps them sealed — efficiency is one of several selection factors.

Heating input (BTU/hr) Gas input rating of the make-up air unit.

Heating hours per year Approximate hours the burner runs over a heating season.

Natural gas price (USD per therm) 1 therm = 100,000 BTU. Use your utility rate.

Direct-fired (~92% efficiency) —

Indirect-fired (~80% efficiency) —

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Direct vs Indirect Operating-Cost Estimator

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