Question about using PVC pipe

[WildWildMidwest]

I am preparing to install our Navien 210A tankless water heater soon. I will do the water pipe and electrical work myself, then hire a licensed plumber to complete the gas installation.

My question relates to use of PVC pressure pipe. Our current domestic pipes are 3/4" soldered copper. I've done quite a bit of modification to our pipes over the years with L-grade 3/4" soldered copper. I recently installed a cycle stop valve, which works beautifully! I bought some decent quality 1" shut-off valves and a pair of 4.5 x 10" water filter housings to prefilter sediment upstream from our tankless heater.

I wonder if there's any reason why I shouldn't connect the valves and filters using 1" white PVC pressure pipes and PVC cement? Is there any safety risk or code violation using PVC for domestic cold water pipes? Will cured PVC cement hold 45-62 PSI over many years without leaking?

PVC would be a cost savings and would take about 1/2 the time to construct versus copper. I can use pre-threaded PVC pieces to make my job easier. I don't plan on using any PVC on the hot water side... just 3/4 inch copper. Thanks.

[SewerRatz]

I would double check with your local plumbing codes. Most cities around by me will not allow PVC or even CPVC to be used. The Illinois code does allow it,but like I said the cities themselves will not allow for it. Also I would not use PVC , if your plumbing code for your city allows you to use a plastic pipe you best off using CPVC.

[jadnashua]

In a conventional WH (may not apply with yours), you cannot use any plastic pipe within (I think) 18" of it. SO, if you have to use copper anyway, I'd probably go all the way. What, if anything does the installation manual say? You may also want to ask your building inspector.

[99k]

The IPC does not allow PVC but CPVC is allowed. It can be used for hot and cold, but as mentioned, stay away from the WH (nipples are sold in the supply store for this). The proper protocol for glueing CPVC is to allow a 24 hr cure time ... not likely to happen. I would use copper tubing or PEX.

[WildWildMidwest]

Thanks for all the feedback. I left a message for our town's plumbing inspector to call me back. He'll be doing our inspection when the heater is installed. I agree it's far better to get pre-approval before starting the work.

[Gary Swart]

Even if plastic pipe is allowed in you area, why would you want to use an inferior medium? You apparently already know how to sweat copper, and that is a much better material than plastic.

[WildWildMidwest]

@ jadnashua,

I will use flexible stainless steel hoses for the last 24" to make future WH removal & servicing easier, so no plastic will be within 18" of the tankless unit. I'll go the extra mile and secure 5/16" cement board to the wall behind the tankless heater as an added fire barrier... which is probably unnecessary but it's only a few bucks. I understand tankless heaters aren't supposed to get hot to the touch. Navien recommends a minimum of 0.5" rear clearance. Just to be sure, I'll leave a 2-4" rear air space to maximize convection surface area and optimize free airflow.

[FloridaOrange]

I understand tankless heaters aren't supposed to get hot to the touch.

The vents can get quite hot.

[WildWildMidwest]

Gary, point taken. It is about streamlining installation and trying to learn something in the process.

I asked my local building supply store's plumbing section staff. They didn't think there was any problem intermingling PVC or CPVC with copper for domestic water pipes. The Watts filter housings are all plastic & acrylic, and Watts' own installation kits and valves appear to be CPVC. But I prefer to stick with quality brass valves whenever possible. Copper connections are certainly optimal, however 1" copper fittings are about 10x more expensive versus threaded CPVC and it's more time consuming to construct.

I'm hearing consensus from you that, regardless of what my store's sales staff said, my shortcut probably isn't well advised. Most of the store staff seem to have no formal plumbing experience. I trust your opinion a lot more than theirs.

[WildWildMidwest]

FloridaOrange,

Navien water heaters are direct vented condensing units. They don't get nearly as hot as noncondensing heaters. According to Navien's Installation Manual:

This navien water can be vented with plastic or stainless steel. Plastic vent can be used in all cases EXCEPT with the incoming or recirculation return water temperatures exceed 160°F (70°C). IF you set the water heater at a temperature higher than 160°F (70°C) AND are running an external recirculation loop or a combination heating system, you MUST use the Navien stainless steel venting or any 3" venting system approved for use with Category IV appliances (typically Type BH Special Gas Vent approved to UL1738-S636.)

[WildWildMidwest]

I just spoke with my plumbing inspector. He agreed that CPVC is within code and it's no problem for cold water connections. I'm not sure what the temperature limits are. PVC is NOT within Wisconsin code for domestic water systems.

Thanks to all for your help.

[hj]

I do not know of any code which allows PVC inside the building. And using threaded PVC would be a disaster waiting to happen.

[WildWildMidwest]

After considering the information here I decided to stick with 100% soldered copper pipe and fittings. While it's a little more work and money, I know soldered copper is the most reliable long-term solution. I purchased copper parts this afternoon.

Thanks to all for providing sound guidance. Terry Love's Forums are a great source of plumbing wisdom and know-how!

[suavecito1177]

Codes in Denver say no PVC. CPVC, copper tubing and Pex are fine. I Prefer Pex and Sharkbite fittings for all my connections. Never have leaks and makes installation a breeze. Also for gas line I use Trac-pipe or Gas-tite, but you can't pick that up at your local hardware store. Usually install most tankless in under 3 hours.

[Scott D. Plumber]

I would not use PVC even if it were allowed by code. (which it is not here in VA)

Also, the stack temps are much lower in the Navien and that's why they let you use PVC for a vent. (Which I also Don't like)

So what happens if you have hard water dn the HX begins liming up? When the efficiencies go down, you know what stack temps do? Yep, they go up! PVC for a tankless vent is a bad idea. But people want to do it anyway.

Also, Don't forget your drain pan if it's going in a finished area! www.thewallsaver.com. I'm a tankless guy and I'm here to tell you that they all eventually reach the end of their life. Some sooner than others.

Go with Copper, PEX, CPVC as allowed by code and your skill level. Good luck.