Plumbing Pipe Sizing IS 1172 — Cold and Hot Water Systems
IS 1172 (Code of Basic Requirements for Water Supply, Drainage and Sanitation) is the foundational Indian standard for plumbing design. For MEP engineers, it provides the loading unit values and demand flow rates needed to size water supply pipes in Indian buildings. This article walks through the complete pipe sizing process with a worked example.
1. IS 1172 Loading Units — Water Consumption per Fixture
Plumbing Fixture | Loading Units (Cold) | Loading Units (Hot) | Flow Rate (L/min) |
WC (cistern flush) | 3 | — | 9 L/flush |
WC (flush valve) | 6 | — | 9 L/flush |
Washbasin (tap) | 1 | 1 | 8–10 L/min |
Shower (mixer) | 2 | 2 | 8–12 L/min |
Bath tub | 3 | 3 | 15–20 L/min |
Kitchen sink (domestic) | 2 | 2 | 10–12 L/min |
Dishwasher (commercial) | — | 4 | 15–20 L/min |
Washing machine (domestic) | 3 | 2 | 12–15 L/min |
Urinal (cistern) | 2 | — | 4.5 L/flush |
Hose bib / garden tap | 4 | — | 15–20 L/min |
2. Simultaneous Demand Factor
Not all fixtures operate simultaneously. The simultaneous demand factor (diversity) reduces the design flow rate from the theoretical sum of all fixtures:
Total Loading Units | Probable Flow Rate (L/min) | Notes |
5 | 12 | Low-rise residential |
10 | 16 | Small floor / flat |
20 | 25 | Typical residential floor |
50 | 42 | Small hotel floor |
100 | 60 | Medium hotel or office floor |
200 | 90 | Large floor plate |
500 | 150 | Full building main supply |
1000 | 220 | Large complex |
Note: Simultaneous demand is derived from IS 1172 probability curves. Actual flow rates depend on usage pattern — hospitals and hotels may have higher coincidence factors than offices.
3. Pipe Sizing from Flow Rate
Once the probable simultaneous flow rate is determined, pipe size is selected to maintain velocity within acceptable limits:
Application | Max Velocity (m/s) | Min Velocity (m/s) | Notes |
Cold water main | 2.0–2.5 | 0.6 | Higher velocity causes noise in CPVC |
Hot water supply | 1.5–2.0 | 0.5 | Lower velocity — thermal expansion |
Cold water risers | 1.5–2.0 | 0.5 | Reduce noise in riser shafts |
Branch to fixture | 1.0–1.5 | 0.3 | Final connections |
Hose station / fire point | 2.5–3.0 | — | Separate fire water pipe |
Pipe Flow Capacity Reference
Pipe Size (OD) | CPVC Flow @ 2 m/s (L/min) | GI / MS Flow @ 2 m/s (L/min) | Typical Application |
20 mm | 25 | 22 | Single flat — bathroom branch |
25 mm | 40 | 35 | Small flat cold water main |
32 mm | 65 | 58 | 2–3 flat riser or hotel room branch |
40 mm | 100 | 90 | Small floor riser |
50 mm | 155 | 140 | Medium riser, 8–10 flats per floor |
63 mm | 250 | 225 | Large riser, 15–20 flats per floor |
75 mm | 355 | 320 | Building main, 25–30 flats |
90 mm | 510 | 460 | Large building main |
110 mm | 760 | 680 | Campus or large hotel main supply |
4. Worked Example — 100-Room Hotel, Each Floor 20 Rooms
Parameter | Value |
Number of guestrooms per floor | 20 |
Fixtures per room | WC × 1, washbasin × 1, shower × 1, bath × 1 |
Loading units per room (cold) | 3+1+2+3 = 9 LU |
Loading units per floor (cold) | 20 × 9 = 180 LU |
Probable flow per floor (from IS 1172 curve) | ~84 L/min |
Selected riser size (cold) @ 2 m/s | 63 mm CPVC (250 L/min capacity) |
Hot water loading units per room | 1+2+3 = 6 LU |
Hot water loading per floor | 20 × 6 = 120 LU |
Probable hot water flow per floor | ~62 L/min |
Selected hot water riser size @ 1.5 m/s | 63 mm CPVC (188 L/min capacity at 1.5 m/s) |
Building cold water main (5 floors) | 5 × 84 = 420 L/min (with 0.85 diversity) |
Building main pipe size | 110 mm (760 L/min capacity — 55% utilisation) |
5. Pipe Materials — Indian Market
Material | Standard | Max Temp (°C) | Pressure (bar) | Best For | Notes |
CPVC | ASTM F441 / IS 15778 | 93°C | 17 bar (cold) | Hot and cold water — most common 5-star | Chemical resistant, smooth bore, no scale |
UPVC | IS 4985 | 60°C | 16 bar | Cold water only | Not for hot — softens |
GI (galvanised iron) | IS 1239 | 60°C | 15 bar (medium) | Cold water mains, fire water | Scale buildup — reduced bore over time |
PPR (polypropylene random) | DIN 8077 | 95°C | 20 bar | Hot and cold — European standard | Growing in India — good hot water performance |
Stainless steel (SS 304) | IS 6913 | 120°C | High | 5-star hotels, hospitals, food industry | Premium — excellent lifespan, no corrosion |
Copper | IS 7534 | 200°C | High | Hospitals, UK/European standard buildings | Limited in India — cost and availability |
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