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How to read a radon system U-tube manometer

Short answer: Uneven liquid levels mean the fan is pulling suction on the soil under your home, which is what you want. Levels that are even (a reading of zero) usually mean the fan is off, has failed, or the pipe is disconnected. Compare today's reading with the one marked when the system was installed; a large change is worth investigating. A manometer shows suction, not your radon level, so you still need to test.

Safety: Leave fan wiring and electrical repairs to a qualified electrician or radon professional. Do not run a radon fan with a disconnected pipe inside the house.

Step by step

  1. Find the installed reading. Most installers mark the starting level on the manometer or a label. Write it down if it is not marked.
  2. Check with the fan running. Read where the two liquid columns sit. Many manometers are scaled in inches of water column; read the difference between the two sides, or the marked scale, per the maker.
  3. Zero or even levels. Check that the fan is running and has power (breaker, GFCI outlet or disconnect switch). Look for a disconnected or cracked pipe or coupling.
  4. Higher than usual. A reading well above the starting mark can mean a blocked pipe end (snow, ice, nest) or water trapped in a low spot.
  5. Retest. After any repair, run a radon test with the fan on. EPA also recommends retesting every two years with a system in place.

Manometers, alarms and test kits

Common questions

What is a normal radon manometer reading?

It depends on the fan and the soil under your home, so there is no single normal number. What matters is that it is not zero and stays close to the level marked at installation.

Why did my manometer drop to zero?

Usually the fan lost power or stopped, or a pipe or coupling came apart. Check the breaker and outlet first.

Is a radon system alarm better than a manometer?

An alarm adds a sound or light when suction drops, so you notice without looking. Many homes have both.

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Related categories: Radon Mitigation Supplies. General information only; follow the equipment maker's instructions and local codes. Updated 2026-11-14.