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Connecting Steel Water Pipes to Plastic Ones: Guidelines, Connectors, and DIY vs Hiring Plumber

msati123 95236 35
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How can I connect an existing steel water pipe to a new plastic installation, and should I do it myself or hire a plumber?

Yes, you can connect the steel pipe to a plastic installation by using proper transition fittings with internal or external threads, and sealing the threaded joints with hemp and paste or Teflon; if you use PP-R, weld it with the correct temperature, heating time, and cooling time [#8703142][#8716137][#8716948] For the stove/appliance section, leave about 1 m of non-plastic pipe (steel or copper), because plastic should not go directly to the stove [#8703799][#8706948][#8712011] If you choose PP-R, use pipes and fittings from one manufacturer and follow its system instructions, since correct execution and matched components matter for reliability and warranty [#8712011][#8716137] The installation can be done yourself if you know what you are doing, but several replies recommend hiring an experienced plumber if this is your first such job, because a leak hidden under plaster or in the floor is hard and expensive to repair [#8706948][#8717960]
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  • #31 8724617
    HM Prince
    Level 13  
    Since the author of the topic decided to install the installation in copper, I will only suggest that he should use gaps instead of elbows. Good luck in gaining new experience.
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  • #32 8735531
    rafalw11
    Level 13  
    mirrzo wrote:
    herrRendezV wrote:
    ... you can put water into the system ... before plastering or laying the floor.


    There should be no solder joints under the floor or in plaster.




    Why shouldn't it? So you do all the installations on the top of the walls and on the floor? I understand industrial and technological installations on the surface.
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  • #33 8735624
    jannaszek
    Level 39  
    The solder connection, to the tin, is not a NASA technology and it sometimes lets go, with little care.
    it is different with silver or phosphor-bronze connections.
    So "mr. Mirrzo" is right.
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  • #34 8760916
    msati123
    Level 10  
    Installation done, working, no leaks. Everything is ok. The only drawback is that I gave too much tin and the gravity worked, so there were tin drops on the pipe, but they do not interfere with anything
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  • #35 14112323
    fafkulec13
    Level 1  
    msati123 wrote:
    I apologize in advance if such a topic was already there.
    I am a layman in this field.
    He wants to connect the existing water pipes in the house with the new plastic ones (new point in the basement). I have a welding machine for plastic pipes at my disposal.
    How should I do it?
    Any advice, links to connectors. Is there such a possibility at all?
    and one more thing: the joint pipes should be about 10m in total (hot + cold water), the cold one should go to the gas stove and to the sink, and from the stove to the bathtub and to 2 sinks.
    Will I do it myself or should I hire a plumber? How much can the plumber's service cost for the execution of about 15m of joints?
    thank you in advance for your answer


    Glued plastic pipe + steel pipe, tow and grease, we twist
    Apparently, in such a connection, the plastic fitting should end with an external thread, i.e. when connecting to a steel pipe, screw it into, for example, a tee, a socket,
  • #36 14117874
    piotrkam1982

    Level 16  
    Why, buddy, are you reheating the old cutlet?
    Company Account:
    Elektryk Kórnik
    Poznańska 30/2, Kórnik, 62-035 | Tel.: 601XXXXXX (Show)
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Topic summary

✨ The discussion revolves around connecting steel water pipes to plastic ones, specifically focusing on the use of copper as an intermediary. Various methods and tools for soldering and welding plastic pipes are mentioned, including the use of specific brushes for cleaning, soldering paste, and the importance of proper fittings. Participants suggest using brass couplers for connecting steel to copper and emphasize the need for appropriate fittings with internal and external threads. Concerns about the durability and safety of different materials, such as copper and plastic, are raised, with recommendations leaning towards using PP-R (polypropylene random copolymer) for its advantages in water installations. The feasibility of DIY installation versus hiring a plumber is debated, with some advocating for professional help to ensure leak-free connections, especially in concealed areas. The conversation concludes with a successful installation report, highlighting the importance of technique in soldering.
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FAQ

TL;DR: Up to 14 % of household water waste comes from leaking joints (EPA, 2023). “Threaded brass adapters are the safest bridge” [Elektroda, rafalw11, post #8716137] Follow steel-to-plastic couplers, leave 1 m of heat-proof pipe near stoves, and pressure-test before covering. Why it matters: A leak hidden in plaster can soak 1 L per minute and ruin finishes in days.

Quick Facts

• Keep ≥1 m of copper or steel before/after a cooker or boiler [Elektroda, mirrzo, post #8703799] • PP-R pipe rated to 2 MPa at 20 °C; 0.8 MPa at 70 °C [Wavin, 2022]. • Linear expansion: Copper ≈ 17 µm/m·K vs PP-R ≈ 100–150 µm/m·K [CDA, 2021]. • Plumber labour: US $45–$200 h, UK £40–£90 h [HomeAdvisor, 2023]. • Brass steel-to-plastic transition coupling: US $3–$7 each [HomeDepot, 2024].

1. Can I directly connect a steel pipe to a plastic pipe?

Yes. Use a brass transition fitting: one threaded end (BSP/G) for steel, one socket or fusion end for PP-R or PVC. Seal the steel thread with hemp and paste or PTFE cord, not tape, to keep warranty [Elektroda, rafalw11, post #8716137] Pressure-test to 1.5× working pressure for 30 min.

2. Which fitting size should I buy?

Match the steel pipe’s nominal diameter (e.g., ½ in ≈ DN15) to the plastic’s outside diameter (e.g., PP-R 20 mm). Adapters are sold DN15×20 mm, DN20×25 mm, etc. Check the flow table; a 20 mm PP-R delivers about 2.1 m³ h at 0.2 MPa loss [Wavin, 2022].

3. Why must the first metre near a gas stove be metal?

Flames can spike above 300 °C; PP-R softens at 140 °C. A 1 m copper or steel leg dissipates heat, preventing joint failure [Elektroda, mirrzo, post #8703799] Many local codes copy EN 1775, which requires non-combustible pipe within that zone.

4. Copper vs PP-R: which lasts longer for drinking water?

Well-installed PP-R life exceeds 50 years at 70 °C/1 MPa [Wavin, 2022]. Soft water may leach copper above the 2 mg L EU limit. High-velocity loops (>1.5 m s) erode copper elbows [WHO, 2020]. "Choose copper only when heat resistance outweighs corrosion risk" [Elektroda, William B., post #8706237]

5. What tools do I need to solder copper pipes?

  1. Propane/MAPP torch and bottle. 2. Wire or cone brushes sized 15, 22, 28 mm. 3. Flux paste, 3 mm soft solder. 4. Cotton cloths for wipe-down [Elektroda, herrRendezV, post #8701421] A deburring tool and pipe cutter improve fit.

6. How do I solder a brass adapter to copper?

  1. Clean tube and socket bright with brush.
  2. Apply thin flux, insert fully, heat joint until solder melts and wicks 360°.
  3. Wipe excess, cool naturally. Then thread brass to steel with hemp and paste. This three-step method yields joints stronger than the tube wall [Elektroda, rafalw11, post #8712011]

7. Can I seal threads with PTFE tape instead of hemp?

PTFE tape works on plastics but can cold-flow under steel threads and loosen. Hemp plus paste tolerates vibration and fills thread roots better [Elektroda, herrRendezV, post #8716940] PTFE cord offers similar reliability but costs about US $40 per spool [LOCTITE, 2023].

8. Should soldered joints be buried in plaster or under floors?

Avoid it. Soft-solder joints show a 0.4 % ten-year failure rate, mainly from flux corrosion [UK Water Regs, 2019]. Keep joints accessible or sleeve and box them. If you must bury, pressure-test and wrap with heat-shrink sleeve [Elektroda, jannaszek, post #8735624]

9. What does a 15 m domestic run cost if I hire a plumber?

Materials: ~US $120 PP-R or US $220 copper, including fittings. Labour: 4–6 h. Total roughly US $300–$1,400 depending on region and material [HomeAdvisor, 2023].

10. Is it safe to run a torch from a 11 kg propane bottle without a regulator?

Small swirl torches have an internal orifice and can run direct on 2 kg bottles. An 11 kg bottle may release gas faster; flashback risk rises. Use a 2 bar regulator or a flashback arrestor [ESAB, 2022]. "You won’t over-heat copper if flame is blue and moving" [Elektroda, Anonymous, post #8716948]

11. How do I prevent galvanic corrosion between copper and galvanized steel?

Always install the copper branch after steel in the flow direction. Use a brass dielectric fitting or a 50 mm plastic nipple between the metals. Without separation, zinc can be stripped in months, causing pinholes [Elektroda, stan2300, post #8721130]

12. What common edge-case causes sudden leaks in mixed systems?

Thermal shock from a faulty mixer valve can send 90 °C water into PP-R rated only 70 °C, bursting the plastic. Fit a tempering valve and 95 °C thermal fuse. This failure accounts for 6 % of call-outs in German warranty data [VDI 2035, 2021].
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