Posted By joe.ami on 20 Aug 2010 11:02 AM
It would be interesting to hear the Water Furnace posistion on PEX for the DSH.......

I asked WF earlier in this thread, but they may have missed my "WF?".  Our installer, who went through WF training, used PEXa in our lines.

While I don't believe the DSH temperature in our system would normally approach 200f at 80psi if everything is working properly, could a failure in a safety system cause a problem?  Had I known about these limitations of PEX, I may have requested copper (and possibly paid more for it.)

What about the different grades of copper pipe that should be used?  I recently heard about green label (heavy wall Type K), blue label (standard wall Type L), and red label (thin wall Type M) copper pipe?

Astm ratings are based on continuous temp and pressure. I again say that 3/4 pex will flow a little more than 1/2" nom M copper. M copper is used mostly in exposed residential plumbing and heating . L copper is used in concealed residential work, commercial plumbing and heating, refrigeration [ACR], processes piping when applicable, etc. K is used for underground plumbing and heating, process piping, refrigeration , etc...Eric

Just got off the phone with a nice gentleman from Heat Controller, Inc. (I had called Climatemaster directly, but they didn't want to talk about any unit not specifically branded with the CM logo).

Anyway, HC Inc. said they don't care if it's PEX or copper, but the diameter is important, and that at least 5/8 PEX or larger should have been used, rather than 1/2. He actually said, "3/4 would be better". The reason is that the system is designed to pull a certain amount of BTU per ton into the hot water tank. Reducing the piping is going to significantly lower the amount of BTUs that can be delivered.

I looked at page 21 (Table 7) in the GeoMax manual for HTV, HTD, HTH series 2 stage equipment for 2-6 tons. Am I looking at the right manual? If so:

Although 3/4" copper is listed, so is 1/2" copper as long as your run is less than 45' each way for a 4 ton unit.

Is your PEX OD 1/2"? The 1/2" PEXa used on our job is close to 15/32 for the ID and 5/8" OD. Would the 1/32" make a big difference, and when hot would PEX expand 1/32"? Would the delta-t (and flow rate) be lower with 3/4" compared to 1/2" pipe? I don't know these answers. Is it worth changing the pipe? If the manual calls for 1/2", and that is what was installed, the installer may not want to change it to 3/4" for free.

Posted By ilgeo on 20 Aug 2010 11:53 AM
M copper is used mostly in exposed residential plumbing and heating.

Don't use M copper anywhere if your water is even slightly acidic.

My HTV Series manual 2-5 tons, 2 stage, Heat Controller Inc, dated 3/22/07 on the back, on page 17 states "using at least 5/8" OD copper...". There is no mention anywhere about using smaller piping for shorter distances. They do write that distances should be kept at a minimum, and no one-way length more than 50 feet.

Stuart, your manual may be correct, or maybe they changed the spec. In any event, I guess my question for anyone that knows is, "Would 5/8" OD copper have superior flow or heat transfer to 1/2" (or 15/32") ID Pex?"

I think we are splitting hairs here. If it works...as an installer, I have no objection. As an inspector, if it is contrary to manufacturers' instructions I would have to ask why. While you might be able to convince me that pex was ok, I would want the same ID as specified.
15+ years ago, when code required 3/4" minimum ID for drains, 3/4" cpvc dropped out of vogue as it was not truely 3/4" ID.
J

Copper and PEX are not the same. I think it is best to have a copper run off the unit even if you went 3/4" PEX from there. The longer the run, the larger the pipe should be. There is no need for a flexible line to reduce vibration in a properly built copper run.

I'm not sure the size of the fittings on the DHW in/out lines, but it looks like probably 1" screw connections...they're huge. A reducing coupling is attached to the 1" screw connections that reduces 1" to 1/2" copper, and makes an immediate 90 degree turn. Then there's about one foot of 1/2" copper piping, then to crimp-on 1/2" PEX, which runs about 25 feet one way to the water heater.