What is the T&P valve and expansion tank on a water heater?

The T&P (Temperature & Pressure Relief Valve) and the expansion tank are two essential safety devices on a water heater:

T&P Valve:

• Located on the top or side of the water heater
• Activates if the temperature exceeds 99°C (210°F) or pressure exceeds 150 PSI (1,034 kPa)
• A discharge pipe (typically ¾ in type L copper) must direct water to a floor drain within 150 mm of the floor
• Should be manually operated once a year to verify proper operation

Expansion tank:

• Required in Quebec since 2008 when the water heater has a backflow preventer
• Absorbs water expansion when heating (hot water takes 4% more volume at 60°C)
• Recommended air pressure: 50 PSI (adjust based on static water pressure)
• Without an expansion tank, pressure can reach 200 PSI+, damaging plumbing and the water heater