Cold & Hot Water Pipe Sizing

Network-first calculator with server-protected calculation engine and the worksheet retained in the original left-to-right calculation sequence.

1. System setup

Add as many additional mains as required. A new main may start from any earlier whole-letter tee, including a tee created by another additional main.
For storage-cistern systems, starting pressure is calculated from the water depth in the cistern and the first A–B drop/rise is then applied automatically. For mains systems, enter the incoming pressure in bar and it is converted to kPa. Cold-water resistance is calibrated to the supplied 10 °C Lamont/BS nomograph; hot-water selections use a smooth-pipe temperature correction.

2. Appliances / outlets

Select an outlet and its loading units and design flow are filled automatically. Then choose the tee on the main run that supplies that outlet. Appliance selection now also chooses the matching terminal automatically. Baths include a 22 mm thermostatic blending valve, mixer showers use a manufacturer pressure/flow curve, and electric showers are identified as cold-mains outlets and excluded from the storage-cistern network. WC isolation/FOV settings remain automatic.

3. Pipe sections

Pipe sections are generated from the total tee count. If a tee starts a second main, the final tee letter is used for that route rather than adding another tee. The residual head at the end of a section is carried into every section that starts at that node.

4. Worksheet

The calculation sequence is kept left-to-right. Pipe sizes are shown as external copper tube sizes; the corresponding internal bore is used automatically for hydraulic calculations. Blue fields are calculated automatically; yellow fields are entered/selected. Length and rise/fall fields clear when selected for a fresh entry. Use Auto size pipes after all lengths, levels and fittings are entered.

1
Pipe Reference
2
Loading Units
actual / equiv
3
Design Flow Rate
L/s
4
Pipe Size
external mm
5
Velocity
m/s
6
Head Loss R
kPa/m
7
Drop + / Rise −
m
7A
Pressure effect
kPa
8
Available Head
kPa
9
Measured Length
m
10
Fittings
equiv m
11
Total Effective
m
12
Pipe Loss
kPa
13
Terminal / Fitting
14
Residual
kPa
15
Residual at End
kPa
16
Surplus / Deficit
kPa
17
PASS / FAIL