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Why Pressure Is Worse Upstairs
A little loss upstairs is normal and unavoidable. The useful question is how much, because the number tells you whether anything is actually wrong.
Water has weight. Lifting it costs pressure, and the loss is predictable: roughly 0.43 psi for every foot of height. A second-floor bathroom about ten feet above the ground floor therefore reads around 4–5 psi lower, and a third floor around 9 psi lower. That is physics, not a fault.
When it is normal
If your ground-floor reading is comfortably inside the normal 45–80 psi band, a few psi less upstairs is expected and you will barely notice it in use. Normal and low ranges as published by Grundfos in its homeowner guide to low water pressure.
When it is not
The tell is the starting point. If ground-floor pressure is already marginal — near or below 40 psi — then the same unavoidable height loss pushes the upper floor into genuinely poor territory. The problem is not the stairs; it is that the supply was low to begin with. Diagnose it as a whole-house problem.
The other pattern worth noticing: if upstairs is fine on its own and collapses only when something downstairs runs, that is a flow restriction rather than height. That has its own page.
What to measure
Take a gauge reading at an outside tap and estimate the height to the affected fixture. If the difference is close to 0.43 psi per foot, the system is behaving as it should and the fix is to raise supply pressure overall rather than to chase anything upstairs.
