Buying a House That Already Has a Radon Mitigation System

You are touring a house and spot a white pipe running up the outside wall with a small fan unit on it, or a capped pipe rising out of the basement floor with a U-shaped gauge attached. The house has a radon mitigation system. Buyers sometimes read this as a warning sign. In most cases it is the opposite: the radon problem this house had is the one that got found and fixed, while the identical house next door may have the same soil and no system at all.

A system is not a defect

Radon comes from the soil a house sits on, not from anything wrong with the house itself. Elevated radon is common across large parts of the country, and the EPA recommends mitigation for any home at or above 4.0 pCi/L. A house with a professionally installed, working system is a house where that recommendation was followed. The question for a buyer is not "why does it have a system" but "does the system work."

How to verify the system works

• Check the manometer. The U-shaped tube gauge on the pipe is the system's heartbeat monitor. The liquid should sit at two different levels in the two arms of the U, which shows the fan is holding vacuum. Liquid level on both sides means no suction: the fan is dead, unplugged, or the pipe is blocked.
• Listen for the fan. A working radon fan makes a soft, steady hum. Grinding or rattling means the fan is on its way out. See the signs in our fan replacement guide.
• Test anyway. This is the important one. A running fan proves the system is on, not that radon is low. Include a radon test in your inspection window exactly as you would for a house with no system. A working system with a result under the action level is the outcome you want documented before closing.

What to ask the seller for

• The installation record. Who installed it, when, and the system design. In states with licensing programs you can verify the installer held a license at the time. Our state directory covers each state's licensing rules.
• Pre-mitigation and post-mitigation test results. The before number tells you what the soil under this house does without a system, which matters for understanding what you are relying on. The after number shows what the system achieves.
• The most recent test. The EPA recommends retesting every two years even with a system installed. A seller with a recent passing result has been maintaining the system. If the newest result is many years old, just run a fresh test during inspection.
• The fan's age. Radon fans are wear items with a typical service life measured in years, not decades. A ten-year-old fan is not a reason to walk away, but it is a future expense worth knowing about.

Red flags worth a closer look

• A manometer showing no vacuum, or a fan that is unplugged. Ask why, and retest.
• A system that discharges at ground level or right next to a window. Proper systems vent above the roofline so the exhaust cannot re-enter the house.
• A homemade-looking system with no documentation. It may still work, but the radon test is doing all the talking at that point.
• An elevated test result despite a running system. This happens: fans weaken, soil conditions shift, additions get built over unmitigated soil. It usually means the system needs service or an added suction point, which is a repair conversation, not a catastrophe.

Negotiating around what you find

If the test comes back low and the system checks out, you are done: file the paperwork and enjoy having this box permanently ticked. If the test comes back elevated or the fan is dead, treat it like any other inspection finding. Ask the seller to have the system serviced by a licensed or certified contractor with a passing retest before closing, or price the repair into your offer. Because the pipe runs and suction points already exist, reviving an existing system generally costs far less than installing one from scratch.

Bottom line

An existing radon system should move a house up your list, not down it, provided you verify it. Check the gauge, get the paperwork, and run your own test during inspection. The houses to think harder about are the ones in the same neighborhood that have never been tested at all.