12:57PM | 05/16/05
Member Since: 05/15/05
1 lifetime posts
my wife and i recently moved into a house more than 100 years old. the house has been completely remodeled, including new plumbing. the problem is low water pressure or volume or whatever the term is. when you have the washing machine running, water barely comes out of the remaining faucets. if 1 of the toilets is flushed, the sink in that same bathroom barely has any water at all. i'm not a plumber, so don't get me wrong, but i always that that the lines coming from the hot water heater should be 3/4" and the supply lines which feed off this line should be at least 1/2". after going under our house, i found that all of the lines are the same size, and i doubt they are even 1/2". they look smaller. also, this house used to be divided into 2 apartments with 2 hot water heaters. there is a line that runs from 1 hot water heater to the other one. could the small lines as well as the 2 hot water heaters be my problem?? by the way, the water department said pressure was great at the meter.


07:10PM | 05/19/05
Member Since: 08/29/04
227 lifetime posts
Indeed you need to have at least 3/4 inch water lines to the water heater and away from the water heater to a bathroom group. No bathroom group should be on less than a 1/2 inch line. Most areas require 3/4 water to the bathroom, unless you are using direct runs from a manifold to each fixture, then you can use 1/2 inch. Many new systems are installed with PEX flexible water lines to each individual fixture. This guarantees adequate pressure. If you have good pressure at the meter, yet you have a pressure loss when you run the washer, you might need to resize. You might also want the city to test for available volume and not pressure.

A 1/8 inch pipe has the same pressure as a 3/4 pipe, but you can get a whole lot more water through a 3/4 inch pipe. If your water service is crushed somewhere in the yard, you might have good pressure, but no volume. Hence you would have a pressure drop whenever you use more water than you can get through the opening.

By the way this can be tested at the outside hose outlet. Most cities know the formula for testing for flow pressure not static pressure.

Raymond VinZant Plumbing Prof.
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