TL;DR
A union fitting is a three-piece threaded coupling, two tailpieces drawn together by a swiveling collar nut, that lets a pipe joint be opened and remade without rotating or cutting either pipe. Gas codes require one at each appliance connection so furnaces and water heaters can be swapped out, and hydronic and compressor piping uses them anywhere service is expected.
What it means
A union fitting is a three-piece threaded coupling, two tailpieces drawn together by a swiveling collar nut, that lets a pipe joint be opened and remade without rotating or cutting either pipe. Gas codes require one at each appliance connection so furnaces and water heaters can be swapped out, and hydronic and compressor piping uses them anywhere service is expected. Ground-joint metal seats seal without gaskets; dielectric versions add an insulator to stop galvanic corrosion where copper meets steel.
Where it sits in the glossary
Union fitting is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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