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How House Plumbing Works

by Don Vandervort, © HomeTips

A house actually has several plumbing systems. Water-supply piping brings water to the house and distributes it to fixtures and appliances, including outdoor sprinklers and other irrigation devices. Drain-and-waste plumbing disposes of used water and waste. Vent piping exhausts sewer gases and provides proper pressure for the drainpipes. Gas piping delivers gas to gas-fired appliances. Some homes have pipe systems that serve specialty needs such as swimming pool plumbing and built-in vacuum piping, for example.

home plumbing diagramIf your house is hooked up to a municipal water system, fresh water travels through the water utility’s pipes until it reaches the meter in front of your house. It passes through the meter, where usage is measured, then through a large gate valve, and then through one or more water pipes to your house and property. If you’ve ever seen water gushing from a fire hydrant, you have some idea of the pressure moving the water along.

Inside your home, that cold-water pipe branches off to deliver cold water to all faucets and water-using fixtures and appliances, including your water heater (it may go to a water softener as well). A second run of pipes carries heated water from the water heater to all faucets, fixtures, and appliances that use hot water. Often, hot- and cold-water pipes parallel each other.

Parallel hot- and cold-water pipes slope slightly to the lowest points so the pipes can be drained through a valve or faucet.

Waste drainage systems take advantage of gravity to channel waste to the sewer line. The soil stack, a vertical run of pipe 3 to 4 inches in diameter, carries waste to a main drain, usually underneath the house, which empties into a sewer or septic tank.

Vents prevent sewer gases from seeping into a house, while traps—water-filled bends in pipes—keep gases from escaping up the drain. Vents branch off below the soil stacks while gases vent through the roof. Plumbing generally is vented through a main vent stack, or there may be a vent stack for each fixture if they are widely separated.

A pipe’s size and material can serve as a fairly good indicator of its function. White plastic, copper, and galvanized (silver-toned) pipes that are from 1/2 inch to 1 inch in diameter generally carry water, though some galvanized steel, black steel, and flexible copper pipes of the same sizes may carry gas.

Large-diameter (1 1/2 inch and larger) black plastic, cast-iron, and copper pipes are often drain-waste-vent pipes.

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