Which Pipe Should You Use Where? PVC or Metal?

Pipe selection in plumbing usually starts with this sentence: “Master, which one is better?”

Answer: there is no “better.” There is the right choice for where you’ll use it. Temperature, pressure, outdoor conditions, and installation speed decide everything. Here’s the answer to “which pipe”:

1) Indoor cold water line

Recommendation: PVC

Why: Cost-effective and quick to install. Indoors, UV/impact risk is low, so it becomes a practical solution.

Watch out: The pressure class (PN) must be selected correctly. Also, hanger/clamp spacing should be proper; if the pipe is left “like a spring,” stress builds up at the joints.

Quick tip: On lines fed by a pump/booster, if there are pressure fluctuations, double-check the diameter and PN selection.

2) Indoor waste water / drainage

Recommendation: PVC

Why: Fast installation, good parts availability, easy maintenance. Waste water lines usually don’t have high pressure; with correct installation, PVC lasts long.

Watch out: The most common mistakes are slope and joints. Too little slope causes clogs; too much slope makes the flow “outrun the solids” and leaves dirt behind. Joints must be clean and properly seated.

Quick tip: Don’t increase the number of elbows unnecessarily; every elbow is a potential clog point.

3) Hot water line (combi boiler / boiler room)

Recommendation: Metal (or a system rated for hot water)

Why: Heat can stress PVC; especially continuous temperature cycling (heating-cooling) fatigues the material and may cause issues at the joints.

Watch out: Insulation and expansion allowance are a must. Expansion is more noticeable on hot lines; if fixed points and supports are wrong, the pipe will push against itself.

Quick tip: On hot water lines, the issue isn’t “sweating,” it’s heat loss. Insulation means comfort and lower bills.

4) Steam / high-temperature water

Recommendation: Metal

Why: Safe operation under high temperature and pressure. In these lines, selection is based on “safety and standards,” not “cost.”

Watch out: Project requirements + suitable connection components. Flanges, gaskets, connection standards, and material compatibility are critical.

Quick tip: In steam lines, the cost of a wrong choice is not just leakage, it’s operational risk.

5) Pump / booster outlet (water hammer risk)

Recommendation: Metal

Why: Water hammer, vibration, and sudden pressure changes stress the line. Metal generally handles it more comfortably.

Watch out: Check valve, expansion joint, and correct diameter. The key is not only the pipe, but the equipment combination. The wrong check valve or wrong diameter can increase water hammer.

Quick tip: If you hear a “thud” when the pump starts, the chance of water hammer is high.

6) Outdoor garden / main supply (UV + impact)

Recommendation: Metal (or a UV/impact-resistant alternative)

Why: Sunlight (UV) and impacts can weaken PVC over time. Outdoors, durability becomes the priority.

Watch out: Corrosion protection and insulation/ducting. If you use metal, protect it against external conditions; leaving a pipe exposed ages any material.

Quick tip: Outdoors, the most common failure cause is not the “material,” but unprotected installation.

7) Outdoor line with freeze risk

Recommendation: Metal + insulation

Why: Freezing causes problems regardless of material. Water expands when it freezes, increasing internal pressure.

Watch out: Insulation, heat tracing cable, drainage. You manage freeze risk not with “pipe selection,” but with “freeze protection.”

Quick tip: Adding a drain valve on a freeze-risk line can sometimes be the cheapest insurance.

8) Chemical environment

Recommendation: Depends on the medium (PVC or stainless/special metal)

Why: Chemical compatibility is the deciding factor. PVC works very well with some chemicals; in some environments, stainless is mandatory.

Watch out: Chemical list + temperature-pressure data. “Chemical” is not one word; every fluid behaves differently.

Quick tip: On chemical lines, even “I’ve used this for years” experience isn’t always enough; data wins.

9) Fire line

Recommendation: Metal (as required by the project/standard)

Why: Standards and safety requirements. Fire system selections are carried out according to the project and the relevant standard.

Watch out: Certified products, PN/DN compatibility, correct connection components. There is no “it’ll do” here.

Quick tip: The biggest mistake in fire lines is listening to habits instead of the project.

Super quick decision rule for choosing pipe

If temperature and risk (UV/impact/freeze/water hammer) increase, go with metal. For low-risk indoor lines where speed and cost matter, PVC is a practical choice.