How to Tell If Your Radon System Is Actually Working

1. Look at the manometer

Somewhere on the riser there should be a small U-shaped tube with coloured liquid in it. When the system is running, the liquid should sit at different heights on the two sides. That offset is the system telling you it is pulling suction. If the two sides are level, the fan is not moving air — either it has failed, it has lost power, or something has blocked or disconnected upstream.

Photograph the manometer when the system is commissioned and stick the photo somewhere you will find it. Comparing against the original reading is far more informative than staring at it cold.

2. Listen to the fan

A radon fan should hum quietly and continuously. Silence means it is off. A rattle, a grind, or a noticeable increase in noise usually means bearings on the way out. These fans run 24 hours a day, every day, and are generally expected to last something in the order of five to ten years, so a fan that has been running since the house was bought a decade ago is living on borrowed time.

The fan should also be outside conditioned space — on an exterior wall, in the garage, or in the attic. A fan mounted in the basement is on the pressurised side of the system, and any leak in that pipework is then blowing soil gas into the house rather than out of it.

3. Look at where the pipe ends

The discharge should terminate above the roof eave, well clear of windows, doors and any air intake, so the gas disperses rather than being drawn straight back in. Pipe that stops at the eave line, beside an upstairs window, or under a soffit is a design fault regardless of how well the rest of it works.

4. Find the re-test

This is the one that actually matters, and it is the one most households cannot produce. There should be a post-mitigation clearance test carried out between 24 hours and 30 days after commissioning, under closed-house conditions, showing what the house read once the system was running. Without it, the manometer only proves that suction exists — not that suction was enough.

Current guidance is to re-test every two years in any case, and after any significant change: a new HVAC system, a finished basement, a major renovation, foundation work, or a fan replacement. Any of those can change the pressure relationships the system was designed around.

If something on that list is wrong

The common failures are a small set: too few suction points for the way the slabs are laid out, a fan undersized for the pressure the system actually runs at, discharge in the wrong place, or sealing that was never done. Diagnosis first — fitting a bigger fan to a system with one point in the wrong place mostly just makes it louder and more expensive to run.