Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Proper 1" NPT connections

Steve Garson_2
Steve Garson_2 Member Posts: 712
I am installing a new circulator and need some guidance on how many threads beyond hand tight should a 1" copper NPT fitting screw into a cast iron flange.


Steve from Denver, CO


    EBEBRATT-Ed Member Posts: 15,751
    The fitting tolerances vary, especially when connecting dissimilar materials probably 2-3 turns past hand tight. Use some Teflon tape and some dope.
  • ChrisJ
    ChrisJ Member Posts: 15,859
    The last few times I used them I had bad luck with copper male NPT adapters, the threads were terrible.

    When making an NPT connection you want to tighten it until you feel the threads bind. Basically, it'll gradually get tighter and tighter, but feel smooth and linear. And then, all at once it'll feel like it gets really tight fast, that's the spot you want to be in, in general.

    I'd highly recommend using a few wraps of good PTFE tape like Blue Monster followed by a coating of pipe dope over the tape. Try to push / thread the tape into the threads with your fingernail after you do all of the wraps and then put the pipe dope on.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • hot_rod
    hot_rod Member Posts: 22,353
    That's a tough question to answer. The threads vary so much from product to product. Hand tight, maybe two turns. Often over-tightening is as much as a problem. Teflon tape and dope tends to allow over torquing the connection. A 12" wrench or pliers should be plenty for a 1" threaded connection.

    Those iron flanges tend to be painted on the threads also, further complicating the joint.

    A sweat flange, or sweat Webstone iso valve smooths out the connection assembly from copper to pump flange :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • MikeL_2
    MikeL_2 Member Posts: 500
    edited April 2022
    To quote a favorite mentor, " it depends ". Condition of the fitting and male / female threads matter, and, the size of pipe wrenches, pliers, arms, work space, and experience all matter, too.
        The more modern flanges have a better tool grip area with square shoulders for better leverage.
       I agree with others regarding tape & dope, but in some cases we'll start with string or ball wicking, then 3 /4 wraps of quality Teflon on top; making sure each is back a thread or two from the end. A light coating of quality pipe dope brushed on clockwise along with the string & tape finishes the assembly prep - 2 or 3 full turns beyond hand tight is usually enough. 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited April 2022
    My first answer is to tighten it enough so it don't leak, but not to tight to crack it.

    BUT I have the best answer. FA-GET-A-BAT-IT! and Use 'Dis

    no need for threads or dope or tape or nothin'

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • delcrossv
    delcrossv Member Posts: 751
    i've had enough bad experiences with copper to iron transitions that I'd use a brass sweat to thread or a Webstone fitting like Ed shows.
    Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.
    EBEBRATT-Ed Member Posts: 15,751
    I have had copper chilled and hot water coils where the MFG brazed female adapters on the coil stub. Dumb.

    Of course, brazing annealed the female adapter and softened it. When we cranked a male adapter into it it bottomed out before it got tight.

    I took it back apart and cut 2 threads off the male adapter re-doped it and it was ok, but I didn't like it.

    I could probably un-brazed the female adapter on the coil, but the stubs were short. Wanted to exhaust the other options.

    Luckly, it didn't leak, my next step was going to be taking the male adapter out and cleaning off the dope & tape and screwing it back in and brazing the two adapters together, but I didn't have to.