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Slant/Fin header size?

baj702 Member Posts: 44
I've got a Slant/Fin 300 steam boiler that, according to the tech guy at Slant/Fin, has *one* 2 1/2 riser. When I calculate the velocity it comes out to 50 ft/s. The instructions specify a 2 1/2 header. This seems pretty fast from what I've read, especially since it doesn't have another tapping for another riser. If I go to a 3" header, that would slow it down to 32 ft/s. A 4" header would slow it down to 18 ft/s. I'm thinking of a 4" header, but I don't get how Slant/Fin recommends only a 2 1/2 header?

Also, I think I'll go about 30" with the riser.

Does any of this make sense?


  • Danny Scully
    Danny Scully Member Posts: 1,415
    All of what you’re saying makes sense @baj702. 4” all the way. I can’t understand how Slant/Fin has one header size for all their galaxys...is it the model with the coil?
  • baj702
    baj702 Member Posts: 44
    Thanks for the sanity check! It's a PZ, so it doesn't have the tankless water provision.

    Where do you normally increase the pipe size? Another post mentioned it doesn't do any good on the riser, so maybe the last 90 of the swing joint into the header should be a 2 1/2 --> 4 90 (if they make one)?
  • Dave0176
    Dave0176 Member Posts: 1,177
    edited November 2017
    5” header gets you down to 12 ft/s

    And yes they only recommend 2-1/2 which to me is insane. That’s why I only use boilers with at least three inch tappings.
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    Paul S_3New England SteamWorks
    EBEBRATT-Ed Member Posts: 15,312
    Most don't agree with me but I feel the risers should blow up bigger as soon as they leave the boiler.

    I think keeping the water in the boiler is better than separating steam from water in the header
  • Steamhead
    Steamhead Member Posts: 16,723
    We just installed a Galaxy PZ300 onto an existing 4-inch header. Looked a bit strange but it runs fine.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
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  • baj702
    baj702 Member Posts: 44
    edited November 2017
    @EBEBRATT-Ed, maybe I should hedge and blowup to 3 inches on the riser and then a 4" header?
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,214
    The Slantfin Galaxy boiler appears to have a built in steam separation inside the casting. It is the only boiler I know that has an extra wide end section in which they run the steam through before reaching the outlet, probably dropping out alot of water along the way. Other boilers have the outlet right at the common connection at the top of the boiler. In addition there appears to be an inclined plane just below the tapping that probably shields the tapping from surging steam and also acts as a steam and water separator. I have always been amazed at how clean the steam is that these boilers produce. Water cannot be suspended in the vertical steam supply pipe unless velocity is over about 30 ft /sec. On a horizontal header placed far enough above the boiler so the foam does not carry over, the water drops to the bottom of the header... you shouldn't need as low of velocity here to delivery good steam to the system. The big thing is to make sure that the water doesn't get pulled up from the bottom of the header into the steam supply. According to Slant Fin having at least 3 pipe diameters between the boiler supply and the system riser ( and any other riser) and at least 2 pipe diameters between the last riser and the equalizer keeps the water down on the bottom of the pipe. I usually tee off the header at the same size as the header and then drop to the main size. This keeps the velocity down at the header connection reducing the liklihood of water getting pulled up into the system. I'd like a 3 inch header with 3 inch take offs, especially if you have some header length for the water to settle to the bottom of the pipe. 4 inch is probably only necessary if you don't provide enough horizontal header to dry out the steam.
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  • I think the Galaxy is a nightmare for steam.
    New England SteamWorks
    Service, Installation, & Restoration of Steam Heating Systems