Spa Pump Plumbing Size - Wet End Orientation
Hot tubs are usually plumbed with either 1 1/2 inch plumbing or 2 inch plumbing.
Wet end orientation can be changed on most pumps in 45 degree increments to line up to your current setup, or the pump may have a center discharge instead of a side discharge - make a note of that when looking for the correct replacement pump. (side discharge pictured above).
Sometimes the spa manufacturer will actually mix pipe or hose sizes within the same spa and use reducers or adapters as needed to complete the plumbing plan.
When replacing a hot tub pump, the size of the plumbing at the unions that connect to the spa pump are what is important.
Why is plumbing size and orientation important? So that you buy the correct unions on either side of the pump that connect to existing plumbing lines without the need to reglue or add any pipe when retrofitting a spa pump. If plumbing meets the pump at 45 degree angles, the wet end of the replacement pump can be rotated 45 or 90 degrees in order to match up with the existing plumbing lines.
STEP 4: Spa Plumbing Size 
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| Spa Plumbing Size 1 1/2 Inch |
Spa Plumbing Size 2 Inch |
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Most hot tubs have either 1 1/2 inch or 2 inch plumbing measured by the I.D. or inside diameter of the pipe.
There is a trick to measuring hot tub plumbing sizes as the measurement is actually different than the plumbing size. Specified hot tub plumbing sizes include 1 1/2", 2", 2 1/2" and even 3" plumbing. See below for the real measurements of the various pipe.
How to Measure Hot Tub Plumbing Size
Standard PVC pipe is measured and referred to by the inside diameter or I.D. measurement. So the part of the plumbing that actually moves the water is say 1 1/2 inches in diameter, but the actual pipe has some thickness too and this is added to the inside diameter to arrive at the total thickness of the pipe.For 1 1/2 inch pipe the outer diameter is actually (O.D.) 1.9" thick
| PVC | I.D. | O.D. | ||
|---|---|---|---|---|
| 1 1/2" | 1 1/2" | 1 7/8" | ||
| 2.0" | 2.0" | 2 3/8" | ||
| 2.5" | 2 1/2" | 2 7/8" | ||
| 3.0" | 3.0" | 3.5" |
So it is important when thinking about spa plumbing measurements that you use the inner diameter, or width of the pipe where the actual water flows through. When you think about it this makes sense and is not dependant on the thickness of the PVC pipe to get the correct measurement.
When you measure a pump union, the same principle applies. You measure the width of the part you can see through and use the inner diameter measurement as your plumbing size.
Chances are it is either 1 1/2" wide or 2".
Whether you are adding a Waterway, Vico, Aquaflo or other brand hot tub pump, check to make sure the plumbing size is compatible with your existing system.
The wet end orientation is usually changeable by rotating the wet end 90 degrees in either direction as needed to accommodate your setup.
Plumbing sizes can be confusing, but remember that 2 inch plumbing refers to the inside diameter of the heater or pipe - not the fitting size.
