How many bar should building water pressure be? About 2 bar at the highest tap is enough. The pump pressure formula for any height, normal tap pressure, mains pressure and the upper limit.
The short answer: about 2 bar at the highest tap in the building is enough. The pump room pressure has to be high enough that those 2 bar still reach the top after the floors have taken their share. Below you'll see how that number is worked out for your building.
Bar, metres and floors
In Iran the usual unit of water pressure is the bar.
- 1 bar is about 14.5 psi.
- 1 bar lifts water about 10 metres.
- Each floor is about 3 metres high, so each floor takes roughly 0.3 bar off the pressure.
Normal pressure at the taps
International sources give 3 to 5.5 bar as normal pressure at the taps of a home. Below about 2.7 bar the flow feels weak. Above 5.5 bar, it gradually damages taps, hoses and the water heater.
What pressure should the building pump give
In a building with a pump and a pump controller, the pump room pressure moves up and down between two numbers: F1, at which the pump stops, and F2, at which the pump starts. The formula for both is simple:
- F1 = (building height ÷ 10) + 2
- F2 = F1 − 1.5
Measure the height from where the pump sits to the highest tap.
| Building height | F1 | F2 |
|---|---|---|
| 10 m (3 floors) | 3.0 bar | 1.5 bar |
| 15 m (5 floors) | 3.5 bar | 2.0 bar |
| 20 m (7 floors) | 4.0 bar | 2.5 bar |
| 30 m (10 floors) | 5.0 bar | 3.5 bar |
In HYDROSET's factory setting, F1 is 3 bar and F2 is 1.5 bar, which suits a building of about three floors. How to change these two numbers is in How to set a water pump controller.
What is mains water pressure
The pressure in the city water network has no fixed value. It differs from city to city, from one neighbourhood to the next, and at peak hours. To know the real number, screw a pressure gauge onto the garden tap or a tap before the pump, and read it at several different times of day. The full method is in How to measure water pressure in a building.
How much pressure does a 1 hp pump give
You can't tell from the horsepower. The pressure a pump builds depends on its head, and the head is printed on the pump nameplate in metres. Every 10 metres of head is about 1 bar of pressure. Two pumps of the same horsepower may have different heads.
The HYDROSET manual rule: the head on the pump nameplate must be more than the building height plus 20 metres. A pump weaker than that never reaches the F1 pressure and runs nonstop.
Maximum water pressure in a building
More pressure than you need brings no benefit, only harm. High pressure damages the solenoid valves in washing machines and dishwashers and shortens the life of the fittings. If the pump room pressure is above 5.5 bar, lower F1 according to the table above. If the high pressure comes from the mains itself, you need a pressure-reducing valve.
See the pressure in action
The pump controller simulator has a pressure gauge on every floor. You can see how the pressure falls as you go up the floors, and how it rises and falls between the pump starting and stopping.
