Challenges to an Expert’s Believability Are Not Relevant at Class Certification Stage


Court: United States District Court for the District of Nevada
Jurisdiction: Federal
Case Name: Hartmann v. Uponor, Inc.
Citation: 2013 U.S. Dist. LEXIS 203164


The plaintiffs brought this product liability class action lawsuit against the defendants claiming the defendants designed, distributed, manufactured, installed, and/or marketed defective plumbing components which caused injury to the plaintiffs. The plaintiffs alleged that the defendants installed defective brass fittings that caused a chemical reaction upon contact with water. This chemical reaction allegedly caused zinc leakage in the plumbing systems of the plaintiffs’ homes resulting in system failures. The plaintiffs claimed that properly manufactured fittings would last at least 50 years. The plaintiffs retained a plumbing expert witness to support these claims, but the defendants proceeded with a Daubert challenge of his testimony.

The Plumbing Expert

The plaintiffs’ plumbing expert had 30+ years of experience in the plumbing construction industry. He was a licensed professional engineer in multiple states who had worked at every level of bidding, managing, and designing construction projects. The plumbing expert witness began his career at a mechanical contracting firm as an estimator. Less than 15 years later, he had managed millions of dollars of mechanical construction work on projects where construction costs cumulatively totalled to over $3 billion. The plumbing expert founded a company specializing in plumbing engineering and design. He also served in the California State Contractors License Board as an industry expert.


The court noted that the expert had been retained for the sole purpose of testifying about how the brass fittings at issue were not designed and built to withstand the conditions they were meant to come in contact with, and not to opine on the science behind the chemical reaction.

The plumbing expert testified that, based on his plumbing experience and engineering education, the brass fittings manufactured by the defendants did not perform as reasonably anticipated for their use. He also claimed that such plumbing components are made to operate without corrosion for at least 50 years. The plumbing expert also testified that chemical reaction of these plumbing components is not a normal process for plumbing systems.

The court noted that the defendants’ argument that the expert’s testimony was unreliable because he did not specify the tests he performed or which components he observed went to the believability of the expert’s opinion and did not concern the court at the stage of class certification.


The expert’s testimony was held to reliable, relevant, and admissible at the class certification stage.