A shut-off valve at the cold water supply pipe to a water heater is specified as necessary by the building code. But we sometimes see a second shut-off valve at the hot water pipe, even though it is not necessary. People that have had the double shut-offs installed say the additional one is good for cutting off hot water to the house, while allowing cold water flow into the water heater, to speed-up flushing out sediment in the bottom when necessary.
The only potential problem we see with two shut-off valves is that it would be possible to isolate the hot water heater from the house plumbing system if both valves were turned off, leaving no room for expansion of the water as it heats—unless there is an expansion tank at the water heater. But that is an unlikely scenario, and the TPR valve would open to release pressure if it got too high anyway.
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Here’s links to a collection of more blog posts about WATER HEATERS:
• Are water heaters required to be raised off the floor?
• What does ECO INSTALLED mean on a water heater data sticker?
• Where are gas water heaters not allowed to be installed?
• Is the minimum size water heater inlet pipe 1/2" or 3/4" according to the building code?
• Can you use a light switch for a water heater disconnect?
• How can I tell if a water heater is HUD-approved for mobile/manufactured homes?
• Can you wire a 240-volt water heater with 120 volts?
• Is it alright to have a shut-off valve on both the hot and cold water pipes at a water heater?
• What is the minimum clearance to doors and windows for an outdoor tankless gas water heater?
• What is required clearance for access and working space in front of an electric water heater?
• Why is the water heater older than the house?
• Does a water heater need a shut-off valve?
• Why should a tankless water heater have an isolator/service valve kit installed?
• When was a gas water heater first required to be elevated 18 inches above a garage floor?
• Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home?
• What is the purpose of a thermostatic mixing valve above a water heater?
• Does a tankless gas water heater still work with no electricity during a power outage?
• Why do water heaters have a sacrificial anode?
• What is the difference between a manufactured/mobile home water heater and a regular water heater?
• Does a tankless water heater require a pressure relief valve?
• Is a catch pan and drain piping required for a replacement water heater?
• What is the difference between a single element and dual element electric water heater?
• What is an FVIR water heater?
• What is a heat pump water heater?
• What is a dielectric union?
• What's that powdery crust on the pipe connections at the water heater?
• What are the most common installation mistakes with water heater replacement?
• Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises?
• What can I do to make my water heater last longer?
• How can I determine the age of a water heater if the serial number is missing or decoding it is impossible?
• How does a hydronic heating system work?
• What does it mean when a gas appliance (water heater, furnace, or range) has been "red tagged"?
• What's the valve with the flip-up handle on the water heater for?
• Why is an older water heater an insurance problem?
Visit our PLUMBING and WATER HEATER pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.