I can't imagine why anyone would have run a 3/4" riser in the first place, but whats done is done so we can only make the best of it.

You second plumber is absolutely correct. All he or she will need to do is come off the mixer with a 1/2" line then install a 3/4"x1/2" reducer to connect to the existing riser at any convenient location. There is no need to tear walls out, but then the first plumber knew that as well. I suspect he or she was just trying to enhance the job to make a few more bucks on you.

Thank you so much for your response.
Was 3/4" pipe not standard during that period (1939-40)?

If my shower riser is 3/4" doesn't that mean I will have a problem replacing the shower trim?

I think the original question was a bit misleading and the problem is more complex than just a size issue.

The post identifies the existing pipe as a ¾" pipe but I suspect that is not the case. Pipe is identified by its inside diameter, not the outside diameter. The follow up response states that the pipe in question is original to the home circa 1939-1940 and while there was some very limited use of copper pipe as early as 1938 in the period from 1939 through 1945 copper was unavailable because it was needed to make brass for military munitions during WWII. After WWII copper was again introduced into the plumbing industry and it began with a relatively slow start until about 1950 when it took off and rivaled galvanized iron pipe as the material of choice until synthetic pipe became available in the late 50Âs to early 60Âs.

I suspect the existing shower riser in the original post is made of Sched.40 galvanized iron pipe which has an outside diameter of approximately ¾". (The actual outside diameter of GIP is 0.840").

If this is the case then it introduces another problem. The only code-approved method of joining iron pipe is by means of NPT (National Pipe Taper) threaded joints. Some shower mixers do have female NPT threads on the ports which could be connected directly to the existing riser, but it would require moving the riser back from the studding enough to permit rotating the whole mixer body while making the connection and if the pipe was properly supported during initial construction that would prove to be very difficult.

In addition, as iron pipe ages it develops a thick layer of mineral scale on the interior of the pipe, often to a point where the pipe only has tiny passage for water and in a worst case the pipe can become fully obstructed. If the riser is galvanized iron pipe it definitely should be changed out, even if that requires opening the wall to do so.

Am I missing something? Maybe it's the neophyte in me, but it doesn't sound that difficult to upgrade it. It's a closet. The "rip it out" phraseology is too much. Just make another access panel higher up at the head height and have it done. If you don't want an access panel afterward, patch it up.

lazypup: I apologize that my first post was so misleading, that was certainly not my intent...I just have no idea what I'm talking about, which is why I'm here seeking help :) Your second post clears things up very well, thank you.

homebound: You're right, "rip it out" was too much. I have no problem with the access panel. My original question was about whether or not it was neccessary, since I was getting different opinions from the two plumbers.

Thanks so much for your responses, I appreciate it.

No apology necessary. I would not expect a homeowner to know plumbing any better than I know heart surgery or international banking. We all have a field of expertise and generally when we step out of it we are totally out of our element.

In fact, if there is any apology in order it is I who should apologize because you did state that the house is circa 1940 in your original post. From that I should have concluded it was a 1/2" galvanized iron pipe, not a 3/4" pipe.

On the other hand, I sincerely hope everyone can appreciate the difficulty in attempting to diagnose problems sight unseen with only vague descriptions from people who are unfamiliar with the trade language. Quite often it takes two or three rounds of discussion before we get all the facts necessary to resolve the problem.

No worries, I figured it'd go back and forth a couple times!