What type of certifications should a company have to test the airflow of my ducts.
Are you talking about a company that does certfied T&B.
Or just your HVAC company that can check air flow.
T&B should have a national cert.
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How many times must one fix something before it is fixed?
Just a HVAC company.
A company does not have to be certified.
Some are though.
If they are, thats a plus.
They may be certified by NCI, or other company.