Mixed Repipe - PEX for Hot Water and Copper for Cold Water?

[Bill Alford]

We have experienced pin hole leaks in our original hot water copper pipes with a recirculating pump.
This may be from Chloramine in the water supply and thinner walled copper - in conjunction with constantly recirculating the hot water. We had not seen pin hole leaks in the cold water supply.

I have read about PEX lasting substantially longer under the Chloramine conditions. However, I have also read about some chemicals leaching for about six months after PEX install due to how PEX is manufactured. These are chemicals I would rather not drink, such as MTBEs.

To solve both problems, I was wondering about repiping the hot water supply through my home with PEX that is recirculated while repiping with thicker copper pipes the cold water supply that is drank from. The PEX solves the pinhole leaks while the copper avoids chemical leaching into the cold water drinking/cooking supply.

The questions -
1) Is mixing the repiping in this manner advisable? What problems do you see, besides costs and melting PEX when copper is torched.

2) The showers/tubs are using pressure balanced valves that mix cold and hot water together. PEX is typically smaller than copper (equal sizing, eg., 1/2 inch) which may result in different pressures at the valves. Is this a problem or am I over thinking this?

 

[SHR]

Do the whole re-pipe in PEX. Unfortunately you have been given misinformation about PEX health hazards. PEX is safe and appears to be superior to copper in chemical resistance and longevity. To answer your second question; the pressure is NOT affected by pipe diameter. The flow rate may change, but a tub/shower valve has inlets smaller than 1/2" PEX so there would be no issues with pressure and flow rate at the faucet.

 

[Sponsor]

 

[Terry]

You can't use PEX on a tub spout.

 

[hj]

quote; To answer your second question; the pressure is NOT affected by pipe diameter.

Dynamic pressure is definitely a function of pipe diameter as is volume, since they are two sides of the same coin.
The failure of hot water piping with a recirculation system is usually at, or near elbows and tees, and is caused by the pump velocity not being throttled to the lowest flow necessary to maintain the temperature. This causes cavitation and erosion at turns.