TL;DR
A thermal expansion tank is a small bladder tank teed into the cold supply near a water heater to absorb the pressure spike created when heated water expands inside a closed plumbing system. Behind a check valve or pressure-reducing valve the expanding water has nowhere to go, driving pressure high enough to weep the T&P valve and stress fixtures.
What it means
A thermal expansion tank is a small bladder tank teed into the cold supply near a water heater to absorb the pressure spike created when heated water expands inside a closed plumbing system. Behind a check valve or pressure-reducing valve the expanding water has nowhere to go, driving pressure high enough to weep the T&P valve and stress fixtures. Residential tanks run about 2 to 5 gallons, and the air charge must be pumped to match street pressure at installation for the bladder to do its job.
Where it sits in the glossary
Thermal expansion tank 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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