Converting Copper to CPVC for a tub / shower

heddaJune 7, 2008


I had to gut our bathroom this week due to multiple leaks and other issues. (it was 35 years old) We have had pin leaks due to ph with the water which have been corrected. However... I am not comfortable with the condition of the copper in the house. I also am not the best with sweating copper and the price is rough. Can I use CPVC for the full tub / shower install? I assume I need to brace the valve, shower line and tub supply. Any quick tips here? Do I need to use wood?


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The Chlorinated Polyvinyl Chloride pipe (CPVC)in sizes ranging from 1/2" through 2" commonly used in residential potable water distribution systems is technically defined as "SDR-11 CPVC-CTS".

The SDR index number defines the pipe wall thickness. Basically under the SDR (Size Dimension Ratio) system the pipe wall thickness is determined by dividing the diameter by the index number, thus a 1/2" SRR-11 pipe would have a wall thickness equal to .5 / 11= 0.045".

CTS indicates the pipe outer wall is made to the CTS or "Copper Tube Standard" thus the exterior diameter of CPVC-CTS pipe is the same as the exterior diameter of copper pipe.

The physical layout of a CPVC-CTS piping system is nearly identical to that of a copper piping system with a couple minor changes.

When connecting any plastic pipe material such as CPVC or PEX to a solid, liquid or gaseous fired water heater the plastic material may not run within 6" of the flue vent piping. Code also requires a union within 12" of the water heater vessel which leaves us 3 possibilities here.
1. If they are approved by your local code, you could install a flex copper water heater supply line and use that to offset a few inches to the right or left of the water heater flue pipe before making a CPVC riser. The flex lines also meet code standard as the required union, however in your case, where acidic water is a problem the use of copper flex lines would not be a good choice.
2.We could install a copper riser until the lines are well clear of the flue pipe, but this introduces another problem. We may not directly couple copper pipe to a water heater steel pressure vessel. If the water heater comes with dielectric nipples pre-packed in the MFG installation kit you could use them, otherwise you would have to purchase dielectric nipples, which would increase your cost about $10. and here again, with a PH problem, this would not be a good choice.
3.The third choice would be to use galvanized iron pipe(GIP) to make a riser or an offset to the side to allow the necessary clearance. GIP may be attached directly to both the water heater pressure vessel and CPVC pipe. Some will argue that GIP has a bad history of internal corrosion obstructing the pipe, however it should be noted that it takes 20 or 30 years for enough corrosion to build up to be a problem. In nearly all cases that would exceed the expected lifespan of the water heater so it is not a problem.

While copper pipe must be supported at 48" increments, CPVC-CTS pipes 1" or less must be supported at 36" increments and for CPVC-CTS 1-1/4" or greater it must be supported at 48" increments plus there must be a support within 12" of any major change in direction.

Where the pipe is run horizontally through bored holes in wood framing the holes in the framing must be slightly larger than the pipe OD to allow movement from thermal expansion or contraction.

When the bored hole is within 1-1/2" of the face of the studding we must install nail plates on the face of the studding to protect the pipe. If running CPVC-CTS through metal studs we must install plastic grommets on the studs then pass the pipe through the grommets.

When installing your tub/shower mixer valve you must first install wooden blocking and attach the mixer to the blocking in accordance with your manufacturers recommendations. The valve must be totally self supporting and may not rely on the pipe for support.

when you install the riser to the shower arm or the drop to the tub spout you must also install wooden blocking and terminate the riser or drop into a "1/2"CPVC x 1/2"FIP Winged elbow". The winged elbow will have a 1/2" slip fitting on the input end to allow connecting directly to the CPVC pipe. On the output end it will have 1/2"FIP (female iron pipe) threads which you can screw a 1/2" threaded shower arm or a 1/2" brass nipple to stub out to the tub spout. The winged elbow has two wing or ear like projections, one on either side of the fitting, with holes through the projections to allow you to screw it solid to the wood bracing. (CPVC pipe must be protected from both direct and indirect exposure to UV light, therefore it should never be used to make a fixture stubout.

Although there are many different methods of cutting CPVC pipe the best method is to use a PVC ratcheting snap cutter.


There are two types of CPVC glue, Yellow glue and Orange glue.

The CPVC "Yellow" glue is a one shot glue that does not require the use of a primer, however check your local codes carefully as many local codes do not permit yellow glue.

CPVC "orange" glue will be listed on the can as "orange" and it is a two part gluing system which requires the use of CPVC primer before applying the glue. Most local codes require the use of the two part orange glue.

Absolutely DO NOT USE PVC glue, ABS glue or a Universal glue. Make sure the glue you select is specifically labeled as CPCV glue.

    Bookmark   June 8, 2008 at 8:24AM
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