Washing machine drain pipes must be 2 inches (51 mm) in diameter. The drain hose that runs from the washing machine to the drain pipe must have a diameter of at least 1-½ inches (38 mm). The pipes that supply hot and cold water to the washing machine must be ½-inch in diameter (13 mm). The hoses that run from the supply pipes to the washing machine should have an interior diameter of ½-inch, with ¾-inch fittings (19 mm) at each end.
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What is the Standard Washing Machine Drain Pipe Diameter?
Updated UPC (Uniform Plumbing Code) requires that all washing machine drain pipes be at least 2 inches (51 mm) in diameter. In the past, drain pipes as small as 1-½ inches (38 mm) were allowed. However, this smaller size is not adequate for most modern washing machines, which drain much faster than older models. So, your washing machine drain line may need to be updated.
What is the Correct Washing Machine Drain Hose Diameter?
A washing machine drain hose should have a diameter of at least 1-½ inches (38 mm). It is essential that the hose diameter is smaller than the drain pipe diameter because the hose must fit inside the drain pipe. Additionally, the hose should not have an airtight fit inside the drain pipe. A gap between the drain pipe and the pipe wall allows trapped air to escape, which promotes better draining. When checking your washing machine drain line it’s also a good idea to make your washing machine P-trap height is correct.
What is the Proper Washing Machine Water Supply Pipe Size?
The supply pipes that deliver hot and cold water to your washing machine must be at least ½-inch in diameter (13 mm). This measurement applies to all pipe types, including PEX, PVC, copper, and galvanized steel. Supply pipes have much smaller requirements than drain lines, so it is usually easy to tell the two lines apart when looking at the plumbing behind your washer.
What Size Hose Do You Need for Washing Machine Supply Lines?
The flexible hose that runs from your supply pipes to the back of the washing machine must have an interior diameter of at least ½-inch (13 mm). Additionally, they should have ¾-inch fittings at each end so they can attach to the supply pipe and the back of the washing machine. I usually use these flexible steel hoses to connect washing machines to the water supply.
How Do You Check Your Washing Machine Drain Pipe Size?
To check the size of your washing machine drain pipe, follow these simple steps:
- Ensure the washing machine is fully turned off.
- Remove the drain hose from the top of the drain line.
- Use a ruler or measuring tape to measure a straight line across the open mouth of the drain pipe at the center (its widest point).
- Measure the diameter of the entire pipe, including the pipe walls.
- 2-inch copper and PEX pipe will have an outside diameter of 2.125 inches (54 mm).
- 2-inch PVC and galvanized steel pipe will have an outside diameter of 2.375 inches (60 mm).
- If the exterior diameter of the pipe is less than 2 inches, it is undersized.
If you do not wish to disconnect hoses to measure the size of your washing machine drain pipe, you can use these calipers for the job. However, rulers and measuring tapes usually provide accurate enough readings that you can tell if the pipe is correctly sized.
How Do You Check Washing Machine Supply Pipe Size?
The best way to check the size of washing machine supply pipes is to:
- Follow our steps for disconnecting your washer to prevent water from spilling onto the floor.
- Disconnect the supply hoses from the supply pipes.
- Use a ruler, measuring tape, or calipers to measure across the mouth of the pipe.
- Include the pipe walls in your measurement—do not simply measure the diameter of the opening.
- Make sure you measure the center of the pipe—measuring off-center will result in an incorrect, smaller measurement.
- ½-inch PEX and copper pipe has an outside diameter of 0.625 inches (16 mm)
- ½-inch PVC and galvanized steel pipe has an outside diameter of 0.840 inches (21 mm)
Once you’re done measuring your supply pipes, take care when reconnecting the hoses. Make sure the cold water supply hose is connected to the cold water supply pipe and the hot water hose is connected to the hot water pipe. Mixing these two up will result in hot water entering the machine when you select a cold water cycle, and vice-versa.
What Happens if Your Washing Machine Pipes are Too Small?
If your washing machine drain pipe or drain hose is too small, the water inside the machine won’t properly drain when the washing machine transitions to the spin cycle. This can result in a backflow of water filling the washing machine tub. This will mix dirty water in with your clean clothes and not properly prepare them for drying.
- An undersized drain pipe or hose prevents water from properly draining.
- Inadequate drain pipes and hoses result in water being trapped or backflowing into the washer.
- Supply pipes and hoses that don’t meet minimum size requirements may not fill your washer adequately.
- If your washer doesn’t get enough water, your clothes won’t be properly cleaned.
In the event your washing machine supply pipes or hoses are too small, your washer won’t properly fill with water. Not enough water means your clothes won’t get fully cleaned. Similarly, you may not get enough hot water for your clothes to be washed at the temperature you selected.
What if Your Washing Machine Pipes are Too Big?
It is usually not a problem if your washing pipes or hoses are larger than required by plumbing code. Larger pipes are generally more effective at draining and supplying water, so your machine will work as intended. The limits set in place by UPC (Uniform Plumbing Code) set minimum sizes for pipes and hoses. Since larger pipes are more expensive, you will rarely find plumbing that is larger than the minimum requirement.
What Should You Do if Your Washing Machine Pipe is Too Small?
A washing machine pipe that is too small should be replaced by a licensed plumber. Failing to fix this problem can result in a washing machine that doesn’t properly wash your clothes or fails to drain. Typically, if the pipes are too small, the hoses are undersized as well. This means that replacing an undersized pipe usually requires you to change your washing machine hoses as well.
What is the Correct Size for Washing Machine Pipes?
The cheat sheet for proper washing machine pipe and hoses sizes is:
- Drain pipe diameter: 2 inches (51 mm).
- Drain hose diameter: 1-½ inches (38 mm)
- Supply pipe diameter: ½-inch (13 mm)
- Supply hose diameter: ½-inch.
Remember, these are the minimum allowable sizes under Uniform Plumbing Code. Pipes and hoses that are larger than this minimum typically will not cause a problem. However, plumbing smaller than the minimum will often result in a washing machine that refuses to work properly.