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How Far Can You Run ¾ Water Line?

When installing a plumbing system, it‘s important to ensure the pipes can reach every fixture unit. Also, ensure how far your pipe can run because the water pressure depends on that.

So how far can you run ¾ water line?

There are several factors like elevation, water pressure, and fixture units to consider when calculating how far you can run a ¾ inch water line. Remember that water pressure drops with an increased number of fixtures, pipe length, and elevation.

Read on to find out what factors affect the length of ¾ inch water line and how far you can run the water line.

Why Is The Length Of A Water Line Important?

Supplying water across your house depends on having pressurized water flowing through your supply line. Many things impede the flow of water through a pipe, including its length. The longer the water line runs, the lower the flow rate.

Though the length of a water line can be ignored over short distances, it affects a pipe’s supply capability with every extra inch. For instance, doubling the length of a 1 ¼ inch line reduces its water delivery by about 33%. Hence, it’s vital to know how far you can run your ¾ line before you install it.

Factors That Affect The Maximum Length Of A ¾ Water Line

how far can you run ¾ water line

Several factors determine how far you can run a water line. Some of them include the following;

Water pressure

Water pressure affects how far a ¾ inch of water line runs in many ways;

  • First, water pressure is one factor that determines how water flows through a pipe. If the pressure is too low and your pipe is long, the water flow at the other end of the pipe will be drastically reduced.
  • Secondly, the water pressure also limits the static head of the water you can pump through the pipe. Static head is the height difference between the water source and where it is being tapped.

A higher static head causes higher pressure, which can exceed a ¾ inch pipe’s pressure rating and lead to leaks. Hence, you can run the ¾ inch pipe up to a certain length, but beyond that, you should find a larger pipe.

  • Finally, higher water pressure requires a pipe with a higher pressure rating to avoid bursting. Since water pressure drops the further a pipe runs, you need more pressure at the beginning of the pipe to ensure enough water flows at the end.

In that sense, the longer you run your ¾ inch pipe, the more pressure you will need at the beginning. If the pipe runs longer than a certain length, the water pressure may surpass its pressure rating and cause it to burst.

Fixture units

The number of fixtures connected to a pipe affects water pressure and flow rate.

Flow rate

The flow rate of a pipe depends on its diameter and the pressure of the water. Assuming you pump water at a constant pressure through your ¾ inch pipe, the flow rate will decrease as you add more fixtures.

Pressure

Since the flow rate decreases as you increase the number of fixtures installed along a line, the water pressure also drops.

Elevation of water source

The water source’s height relative to the point of use affects the pressure of the water and determines the length of pipe needed. That means the higher the water source, the higher the water pressure. So you can use longer pipes without compromising the flow rate.

However, elevation changes along the water line may still affect pressure, reducing how far you can run the pipe.

Pipe material

Different pipe materials have different pressure ratings. Hence, the material your pipe is made of directly determines the maximum pressure it can withstand.

How Do You Calculate How Far You Can Run A Water Line?

Calculating the length of a water line requires the following information;

  • Total number of fixtures to be installed
  • The elevation of the highest fixture unit
  • Water pressure at the water supply

The process for calculating the maximum length possible is as follows;

Step 1: Count the fixture units

The first thing to do is count the number of fixtures installed along the pipe’s length. This will indicate how much water will be demanded from the pipe. Add the values of each fixture to find the total. You can find the values of each plumbing fixture in the table below.

WATER SUPPLY FIXTURES UNIT (WSFU) AND MINIMUM FIXTURE BRANCH PIPE SIZES

APPLIANCES, APPURTENANCES OR FIXTURES MINIMUM FIXTURE BRANCH PIPE SIZE (inches) PRIVATE PUBLIC ASSEMBLY”
Bathtub or Combination Bath/Shower (fill) 1/2 4.0 4.0  
1/4 inch Bathtub Fill Valve 3/4 10.0 10.0  
Bidet 1/2 1.0  
Clothes Washer 1/2 4.0 4.0  
Dental Unit, cuspidor 1/2 1.0  
Dishwasher, domestic 1/2 1.5 1.5  
Drinking Fountain or Water Cooler 1/2 0.5 0.5 0.75
Hose Bibb 1/2 2.5 2.5
Hose Bibb, each additional 1/2 1.0 1.0  
Lavatory 1/2 1.0 1.0 1.0
Lawn Sprinkler, each head 1.0 1.0  
Mobile Home, each (minimum) 12.0
Sinks  
Bar 1/2 1.0 2.0  
Clinical Faucet 1/2 3.0  
Clinical Flushometer Valve with or without faucet I 8.0  
Kitchen, domestic with or without dishwasher 1/2 1.5 1.5  
Laundry 1/2 1.5 1.5  
Service or Mop Basin 1/2 1.5 3.0  
Washup, each set of faucets 1/2 2.0  
Shower, per head 1/2 2.0 2.0  
Urinal, 1.0 GPF Flushometer Valve 3/4 See Footnote
Urinal, greater than 1.0 GPF Flushometer Valve 3/4 See Footnote
Urinal, flush tank 1/2 2.0 2.0 3.0
Urinal, Hybrid 1/2 1.0 1.0 1.0
Wash Fountain, circular spray 3/4 4.0
Water Closet, 1.6 GPF Gravity Tank 1/2 2.5 2.5 3.5
Water Closet, 1.6 GPF Flushometer Tank 1/2 2.5 2.5 3.5
Water Closet, 1.6 GPF Flushometer Valve I See Footnote
Water Closet, greater than 1.6 GPF Gravity Tank 1/2 3.0 5.5 7.0
Water Closet, greater than 1.6 GPF Flushometer Valve I See Footnote

Step 2: Find the highest fixture’s elevation

In this step, you should find the difference between the elevation of your water supply and the highest fixture along the pipe. The elevation is crucial because it affects the water pressure.

Step 3: Find out the pressure

To calculate water pressure in the water line, start by finding the static water pressure at the water supply. Then, use the highest fixture’s elevation to calculate the pressure drop or gain.

The higher you go from the water supply height, the lower the pressure. Generally, you can expect a loss of about 0.5 psi every time you gain a foot in elevation.

Conversely, water pressure increases when the highest fixture along the pipe is below the water supply’s elevation. Hence, water pressure will increase by 0.5 psi every time you lower the elevation by a foot.

The table below shows the maximum length of a pipe depending on the pressure range.

Image: https://kingcounty.gov/

Using the total value of fixture units, and static pressure from the water supply, you can find the maximum pipe length from table 610.4. For instance, let’s assume the value of all your fixture units is 15, and the water supply pressure is 57 psi.

  • The pressure range in table 610.4 will be 46 – 60 psi
  • Since the fixture value is 15, and your pipe is ¾ inch, its maximum length is about 100 feet

Final Words

There are several factors that determine how far you can run a ¾ water line, including water pressure, elevation, and the number of fixture units. If the water pressure is too low, the flow rate in a long pipe will drop to unusable levels. Installing too many fixtures at a high elevation has the same effect.

To calculate the allowed length of a pipe, you should first find out the total value of fixtures along the pipe. Then find the elevation of the highest or lowest fixture and the pressure at the water supply. You can then use plumbing code tables to find the maximum possible length of your pipe.