Radon manometer reading explained: what the U-tube on your mitigation pipe means, what even levels mean, and when to call the installer

If you came here hoping the gauge would tell you your radon level, it cannot: a U-tube at exactly the sticker value says nothing about the air upstairs, and the only instrument that does is a radon detector or test kit.

What does the U-tube actually measure?

A U-tube manometer is a bent tube of coloured liquid with one end open to the room and the other connected by a small tube to the radon pipe. The fan pulls air out of the pipe, so the liquid on the pipe side rises and the room side falls, and the distance between the two levels is the suction in inches of water column (in. WC). RadonAway’s Easy Read U-Tube Manometer, part 50017, has a scale from 0 to 4.5 in. WC with an adjustable zero, and the maker says it is not suitable for systems above 4.5 in. WC.

EPA’s Consumer’s Guide to Radon Reduction says a warning device must be installed to alert you if an active system stops working properly, lists a liquid gauge, a sound alarm, a light indicator and a dial gauge as examples, and says it must be placed where it can be seen or heard easily. The guide calls the usual device a manometer and says to look at it on a regular basis.

The suction figure depends on the soil under the slab and on the fan, which is why the installer writes the start-up reading on a sticker beside the gauge (Minnesota Department of Health). If the fan itself is the question, the radon mitigation fan review compares the published pressure and airflow figures of the common replacement models.

What does your reading mean?

Compare what you see to the sticker, not to a figure from a forum. No regulator or manufacturer document opened for this page prints a single normal range for all homes, so this table turns on the installer’s value and the fan maker’s maximum.

The Minnesota form puts tubing and power before the phone call because a loose tube reads exactly like a dead fan. The zero is set with the fan running at installation; a practitioner write-up from Energy Vanguard names zeroing with the fan off as the common mistake, a method point rather than a number this page relies on.

What is the fan’s maximum pressure?

A higher reading is not a better reading. RadonAway’s IN095 Rev F manual tells the installer to verify at the annual check that the system vacuum pressure is within the normal operating range and below the maximum recommended operating pressure, and to add suction points if it is exceeded. The maximums below are the makers’ printed figures at sea level; RadonAway says to reduce them by about 4 percent per 1,000 feet of altitude and by a further 10 percent in high-temperature environments.

A sticker value close to the fan’s maximum means tight soil and little air moving, a question for the installer rather than for a bigger fan bought on your own. Fantech’s Rn1 sheet, for example, defines its 0.9 in. WC maximum as the pressure at which the fan operates but moves no air.

When does the gauge fail you?

The gauge reports the fan, not the result. The Minnesota form asks for a short-term retest between 24 hours and 30 days after installation, a retest every 2 years while a system is installed (every 5 years in a building without one), and a retest at sale and after an addition, a reconfiguration, a heating or cooling change that alters pressure relationships, or extensive weatherization. EPA’s Consumer’s Guide says the fan should never be turned off and must run continuously, that fans may last five years or more with maker warranties that tend not to exceed five years, and to retest in the lowest lived-in area after remodeling. Read the result against EPA’s bands in the radon level guide.

What should you do first?

1. Photograph the gauge next to the installer’s sticker, so the baseline is on your phone.
2. Put a monthly reminder in the calendar: the Minnesota form’s interval for checking both the U-tube and any audible alarm.
3. If the levels are even, check power at the fan and the tubing at the pipe tap, in that order, then call the installer.
4. If the reading has moved significantly from the sticker either way, call the installer; do not re-zero the gauge to make it match.
5. Retest every 2 years regardless of what the gauge says, and sooner after the changes Minnesota lists. A continuous radon monitor covers the gap between lab tests; a PM2.5 and CO2 monitor does not read radon.
6. On a private well, radon can also arrive in the water, which a soil-suction system does not touch: see the uranium and radon in well water guide. A system drawing on a sump pit depends on its sealed lid, so check a sump pump that is not turning on at the same time.

Frequently asked questions

Sources

1. EPA, Consumer's Guide to Radon Reduction (2016 PDF) (government or regulatory source)
2. EPA, How do I know if my radon mitigation system is working properly? (government or regulatory source)
3. Minnesota Department of Health, Radon Mitigation System Important Safety Information (OM&M form, PDF) (government or regulatory source)
4. RadonAway, RP/GP/XP Pro Series Installation Instructions IN095 Rev F (PDF) (manufacturer or vendor document)
5. RadonAway, Easy Read U-Tube Manometer (Blue), SKU 50017 (manufacturer or vendor document)
6. Fantech, Rn1 radon fan specification sheet (PDF, distributor-hosted copy) (manufacturer or vendor document)
7. Energy Vanguard, How to read a U-tube manometer (method only) (manufacturer or vendor document)