Living with a radon mitigation system: the manometer, the fan and retesting

A radon mitigation system is one of the simplest systems in a house: a pipe, a fan and a gauge. Once it's installed and the follow-up test confirms it works, it needs very little from you. "Very little" isn't nothing, though. EPA compares radon systems to a furnace or chimney: they need occasional maintenance. Here's what to check, what the readings mean, and when to retest.

What you have

Most homes with a basement or slab foundation get an active subslab depressurization system. A pipe goes through the floor slab (or into a sump or drain tile), runs up through the house or along the outside, and ends above the roofline. An in-line fan in the pipe, located in an attic, garage or outdoors, pulls soil gas from under the house and vents it high into the air, where it dilutes quickly. Crawlspace homes usually have a sealed plastic membrane over the dirt floor with the same pipe and fan. Our guide to radon mitigation systems covers the designs.

EPA's installation standards include several features you can see:

• a warning device that tells you if the system stops working, placed where it can be easily seen or heard;
• a label on the system, so no one changes it by accident;
• an exhaust that vents above the roof and at least 10 feet above the ground, and away from windows and doors;
• a fan that is not located in or below living space.

The manometer: your system's dashboard

EPA lists several kinds of warning devices: a liquid gauge, a sound alarm, a light indicator, or a dial gauge. By far the most common is a U-tube manometer: a small clear tube shaped like a U, mounted on the vent pipe, partly filled with colored liquid.

How to read it

One side of the U is connected to the inside of the pipe. When the fan is running, it creates suction in the pipe, which pulls the liquid up on one side and down on the other. The difference in height between the two columns shows how much suction the fan is creating.

• Levels uneven (a gap between the two sides): the fan is pulling suction. The system is running.
• Levels even (both sides at the same height, often reading "0"): there's no suction. The fan has stopped, lost power, or the pipe is disconnected or blocked.

Many installers mark the reading on the day of installation, or write it on the label. Small changes over the seasons are normal, because soil moisture, frost and snow cover affect airflow under the house. A big change from the installation reading is worth a call.

How often to look

EPA says to look at the warning device "on a regular basis." A practical habit is to glance at it monthly, or when you change your furnace filter or test smoke alarms, and after any power outage or electrical work.

If it reads zero

1. Check whether the fan is running. You can usually hear or feel a slight vibration at the fan, or hear airflow at the pipe.
2. Check the breaker and any switch or outlet the fan is plugged into. Fans are often on a dedicated circuit, and an accidental flip of the switch is a common cause.
3. Look for a disconnected pipe joint, especially after work in the basement or attic.
4. If the fan has power and still isn't running, it likely needs to be replaced. Call the installer, especially if it's under warranty.

If you have an alarm instead of a gauge, test it as the installer showed you, and replace its battery if it has one.

The fan

Never turn it off. EPA is emphatic: the fan should never be turned off; it must run continuously for the system to work. Radon levels climb back up within hours to days once the fan stops.

Expect to replace it eventually. EPA says fans may last five years or more, and manufacturer warranties tend not to exceed five years. Many last much longer, but plan for a replacement at some point. Replacement cost depends on labor and materials, so EPA suggests getting estimates from qualified mitigators before work begins.

Electric cost. Systems that use fans are more effective, but they slightly increase your electric bill, and most systems cause some loss of heated or cooled air. If your bill jumped noticeably after installation, ask the contractor about fan size and sealing.

Noise or vibration. A new rattle, hum or whistle can mean a failing bearing or a loose mount. It's worth a service call before the fan fails.

Retesting

A system that worked on day one can lose effectiveness. Foundations settle, a sump lid gets left open, or a fan weakens. EPA's guidance:

• After installation: test within 30 days of installation, but no sooner than 24 hours after the system starts running with the fan on. Use a 2- to 7-day test with windows and doors closed for 12 hours before and during the test, apart from normal entry and exit. EPA recommends an independent test, either by a separate tester or with a kit you place yourself.
• Every two years: EPA says it's a good idea to retest your home at least every two years to be sure radon levels remain low.
• After remodeling: retest in the lowest lived-in area after you remodel, to make sure the construction didn't reduce the system's effectiveness.
• If you start using a lower level: if you finish a basement or start sleeping downstairs, test there.

Our guide to short-term vs. long-term radon tests explains which test to use, and the radon level calculator compares your result with EPA's action level.

Remodeling and additions

Construction is the most common way a working system gets broken. Before you remodel:

• Tell your contractor where the system is. Pipes get rerouted, walls close over the manometer, and new floor penetrations break the seal on the slab.
• Ask whether changes could void the warranty. EPA suggests discussing this with your radon contractor before the work.
• Plan for additions. If you're adding a new foundation, EPA says to ask your radon contractor what measures should be taken to keep radon low throughout the home, such as extending the suction system or roughing in a separate pipe.
• Keep the manometer visible. If it gets boxed in, have it moved where you can see it.
• Retest when the work is done.

Other equipment

Some homes have a heat recovery ventilator (HRV) as part of radon control. EPA says the HRV filter needs periodic cleaning and should be changed twice a year, and the outdoor fresh-air vent needs to be inspected for leaves and debris. The ventilator itself should be checked annually.

Crawlspace membranes can tear when someone works under the house. After any crawlspace work, check that the plastic is intact and still sealed at the edges and seams.

When you sell

A working, documented system is a selling point. EPA's Home Buyer's and Seller's Guide to Radon covers how radon is handled in transactions. Have these ready:

• the original contract, system description and warranty;
• the pre-mitigation and post-mitigation test results;
• any later retest results and fan replacements;
• written operating and maintenance instructions.

A buyer's inspector will likely run a new test, so make sure the fan is running and the manometer shows suction before the house goes on the market. Our guide to radon when buying or selling a home covers testing during a sale.

Monthly and yearly checklist

Monthly

• Look at the manometer or alarm. Liquid uneven means it's working.

Yearly

• Listen to the fan for new noise.
• Check that the exhaust is clear (no bird nests or ice buildup at the top) and the pipe joints are sealed.
• Check the crawlspace membrane and the sump lid seal, if you have them.

Every two years

• Retest with a short-term test in the lowest lived-in level.

After remodeling, a fan replacement, or a big change in the manometer

• Retest.

If you haven't tested yet or want to know your county's radon zone, start with the ZIP lookup, then test. Every home should be tested, whatever the zone.