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


SteveSteam Member Posts: 12
Could someone please explain milinches to me and what it has to do with flow in a hydronic heating system?


  • Gordy
    Gordy Member Posts: 9,514
    edited May 2013
    Friction loss

    Millinches is another measurement for friction loss of various pipe sizes per foot.

    Usually friction loss in a hydronic system is described in feet of head. The higher the friction loss of piping in a system, or loop of a system the more pump energy needed to maintain a given flow rate.

    As pipe diameter increases friction loss decreases at the same flow rate.

    Or as pipe diameter increase the ability to increase flow rates goes up.

    So if your designing a hydronic system pipe sizing is important to have the ability to carry the most btus with the least amount of pump energy, but yet maintain fluid velocities in an except able range 2-4 fps. High enough velocity to keep air entrained to be carried back to the air removal component, but low enough as not to cause noise , or pipe erosion.

    Darcy Weisbach assigns friction values to various pipe materials and the smoothness of their pipe walls. Example pex walls are smoother than steel pipe so pex friction loss is less than steel pipe for same inner diameter.
This discussion has been closed.