HarleyTechTalk

a friend of mine recently moved into a brand new house.  I was over the checking the joint out and I happened to notice that the piping to the pressure relief valve on the hot water heater was PVC, or maybe it was C-PVC, I am not 100% sure.  Either way I was told in one of my previous house purchases that the pressure relief pipe should always be copper.  this was due to the fact that the PVC pipe could melt and close itself off with the sudden blast of hot water.  was it code that the PRV pipe has to be copper or was that just a better way to do it? 

I think local building codes depend upon the local governing body's ordinances (city, county, etc).  Some cities fire codes for instance require electrical conduit for wiring in the walls while others do not.  Some have started to require a pan with an outside drain to be installed under a water heater (in case the heater "rusts out" and dumps 30 gallons on the floor.  I think the insurance industry championed this one.) Others require it only on new construction (existing houses are grandfathered) while others will require it if you replace the water heater whether the house is new construction or not.  If you don't apply for a building permit, it is quite possible that no one would notice so you "get away with it" because there is no one alerted to check your work.  So a homeowner replacing his own water heater is probably ignorant of the local building codes or even the need for a building permit, so there is no telling what they might do.  Probably use whatever is cheapest.

This is the reason a plumber has to be licensed in the municipality(ies) in which he is working.  He has to show that he knows THEIR building codes.

So the answer is your friend will have to see what the building codes for plumbing are for the area of his home.  Personally, I would want the copper, but I recently replaced an outdoor condensate discharge at our church with PVC - which is "against code".  Ever time I replaced it with copper, the copper thieves would break it off again - its off the third story air handler so there is enough copper pipe to be worth their time.  Since I replaced it with PCV, it hasn't been touched.  I'll argue with the city inspector if he ever notices it, but I have no reason to think he will.  The PVC will deteriorate in the sun while the copper will not, but it will take a few years, so I still come out winner.

Well said Desperado.

Our WH is in the attic here in Houston - good thing I know a drywaller (me) if it ever rots through up there eh?
We're actually lucky enough to get our HVAC service / inspection done by the exact same gent that hung this tin in new construction back in '76 - he eyeballs the WH for me when he's checkin the AC / Heat - I hate to see him retire but I bet it'll happen sooner than later - I reckon he's in his mid 60's but I never asked.

The local code here says it has to be copper. However, hot water shouldn't be over 125 F and that won't melt PVC so I think it's overkill.

And, as George Carlin used to say "They should be called cold water heaters, hot water need not be heated".

Quote from: Desperado on October 07, 2009, 01:34:02 PM
  The PVC will deteriorate in the sun while the copper will not, but it will take a few years, so I still come out winner.

I ran a 3/4" PVC drain from my swamp cooler down to some trees about 5 years ago, I thought it would deteriorate in the sun. El Paso , Tx 100* heat, etc. Still in great shape reg. white schd. 40.         

Quote from: SoonerSoftail on October 08, 2009, 06:23:07 AM
The local code here says it has to be copper. However, hot water shouldn't be over 125 F and that won't melt PVC so I think it's overkill.

The pressure relief valve is not there to handle "normal" conditions.  It is there to handle an over pressure problem.  If the thermostat on your water heater goes crazy and stays on, your water temp can easily rise above the lower end of the melting point range for PVC (100-260C) and the pressure inside your tank will sky rocket at those temps too.  I don't think it's overkill at all considering what could happen if the PVC did melt and close off the pressure relief outlet.  It's typically a short run of pipe and using copper would add little to the overall cost of a water heater install.

-Craig

Quote from: CraigArizona85248 on October 08, 2009, 07:01:09 AM

Quote from: SoonerSoftail on October 08, 2009, 06:23:07 AM
The local code here says it has to be copper. However, hot water shouldn't be over 125 F and that won't melt PVC so I think it's overkill.

The pressure relief valve is not there to handle "normal" conditions.  It is there to handle an over pressure problem.  If the thermostat on your water heater goes crazy and stays on, your water temp can easily rise above the lower end of the melting point range for PVC (100-260C) and the pressure inside your tank will sky rocket at those temps too.  I don't think it's overkill at all considering what could happen if the PVC did melt and close off the pressure relief outlet.  It's typically a short run of pipe and using copper would add little to the overall cost of a water heater install.

-Craig

I must not have been completely awake this morning. Duh, I know that. Feeling stupid now.

Whats wrong with copper? I might use PVC if the thing is outside.

I'm sure the code may vary from place to place, I used galv. with a clean cut on the end (threads are against code) . That said, I fail to see how soft, molten plastic would seal off anything, even if you wanted it to 

Quote from: Glenn W on October 08, 2009, 06:00:36 PM
I'm sure the code may vary from place to place, I used galv. with a clean cut on the end (threads are against code) . That said, I fail to see how soft, molten plastic would seal off anything, even if you wanted it to 

I thought about that too.  Can't see how it would with water running through the pipe under pressure.  But then I thought of this... the pressure relief valve gets reset, the water stops, the pipe is melted and gooey and collapses onto itself, nobody notices... then some time later the scenario with the thermostat repeats.  Now you have a closed off pipe after the pressure relief valve.  I know... a lot of "if"s but possible.  That's all I could come up with.

-Craig

National Building Code says that CPVC, Pex, copper, galvanized, are acceptable for relief valve piping

NO PVC