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SESK: Stuff Everyone Should Know · sesk.info/epa-nitrogen-leak-test

Which gas should be used to pressurize a system for leak testing?

Nitrogen, never oxygen or compressed air.

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  1. Compressed shop air
  2. Dry nitrogen ✔
  3. Oxygen

Why: EPA's Core test topics call for nitrogen rather than oxygen or compressed air for leak detection. Lennox's instructions agree and say compressed air or oxygen shall not be used for purging.

Huh, didn't know that: EPA's Type 2 outline ranks nitrogen alone as the best leak test gas, ahead of nitrogen with a trace of R-22.

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References

Answer: Dry nitrogen. EPA's Core test topics call for nitrogen rather than oxygen or compressed air for leak detection. Lennox's instructions agree and say compressed air or oxygen shall not be used for purging.

  1. Section 608 Technician Certification Test Topics, US EPA www.epa.gov/section608/section-608-technician-certification-test-topics
    Use of nitrogen rather than oxygen or compressed air for leak detection
    Checked 2026-10-10.
  2. Lennox installation instructions 508844-01 (R-454B split system) www.lennox.com/dA/eb5bdb59f2/508844-01b.pdf
    Compressed air or oxygen shall not be used for purging
    Checked 2026-10-10.

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