Nibco 4733-LF Union CPVC Slip x Copper Silicon Alloy Solder - Lead-Free*, CPVC-CTS

The Nibco 4733-LF union is built for exactly that transition. One end is a female CPVC socket that solvent welds to CPVC CTS tube, and the other is a copper silicon alloy cup that solders to copper. So the CPVC side is glued, the copper side is sweated, and the union nut in the middle lets you break the joint later without cutting pipe.

Both 1/2 inch and 3/4 inch are made, ordered as M25010L and M25015L. Size to the CPVC CTS tube, not to nominal iron pipe: this is a copper tube size fitting, so a 3/4 inch CTS union takes 3/4 inch CPVC and 3/4 inch copper. Mixing sizes across the union is not an option here, each part number is the same size on both ends.

Yes, up to 180 degrees F. That covers domestic hot water service on a residential or light commercial system. Above that, or on any line that could see steam or an uncontrolled boiler temperature, the CPVC side is out of its range and you want an all-metal fitting instead.

Lead-free, and certified by IAPMO Research and Testing. That is the certification a plumbing inspector looks for on a potable water transition fitting, and it is why this union goes into drinking water lines where an ordinary brass adapter may not pass.

No. The 4733-LF is not for compressed air or other gases, water service only. Plastic fittings on air lines fail by shattering rather than splitting, so this is a hard no regardless of the pressure you are running.

Break the union first. Unthread the nut, sweat the copper silicon alloy cup onto the copper line on its own, let it cool, then solvent weld the tan CPVC socket half onto the CPVC tube and thread the two together. Soldering with the union assembled puts torch heat straight into a CPVC body rated to 180 degrees F. Nibco publishes plastic fittings installation instructions covering the solvent weld side.

Use the union where you will need to take the joint apart again, at a water heater, a pump, a backflow device, or any piece of equipment that gets serviced. The 4733-LF is meant for line repair and for that reason: the nut unthreads and the two halves separate without cutting into either the CPVC or the copper. A plain socket x cup adapter is cheaper and lower profile, but once it is glued and soldered, the only way out is a saw.

The body is CPVC in the standard tan color used for CPVC CTS hot and cold water tube, so it matches the tan CPVC pipe running in most residential and multi-family potable systems. If your existing plastic is white PVC or gray CPVC schedule 80, this is not the same system and the solvent cement and pressure ratings differ.

Nothing is included beyond the union itself. Plan on CPVC solvent cement (and primer if your jurisdiction requires it) for the socket end, plus lead-free solder and flux for the copper cup end. Since this is a lead-free potable fitting, the solder has to be lead-free too or the certification on the fitting buys you nothing at inspection.