Radon Testing in Minneapolis, MN

An Hourly Record, Not a Single Number

A charcoal kit sent to a lab reports one figure averaged over the whole exposure. A continuous monitor records every hour, and in a Minnesota house the difference is real. A basement can idle around 2 pCi/L on a mild afternoon, then climb well past the action level overnight once the furnace starts cycling and the frozen ground outside leaves the house as the easiest way out. Both patterns can produce the same average. Only the hourly record shows you that the peak lands while somebody is asleep downstairs.

Shut the House Twelve Hours Ahead

Radon readings follow ventilation as closely as geology. Closed-house conditions start twelve hours before the monitor goes on and last until it comes off: windows shut, exterior doors used only for normal coming and going, whole-house fans and window units off. In a Twin Cities winter that is simply how people live anyway, which is one reason cold-season results are so useful. In May or September it takes discipline, and a test run with the porch door propped open measures a house nobody lives in.

Which Floor Counts in a Twin Cities House

The rule is the lowest level that is lived in or could reasonably be finished. In a Minneapolis bungalow that is the basement, even if today it is only the laundry and the old coal room. In a Bloomington or Eagan split-entry it is the lower level with the family room — half above grade, but its floor and back wall are against soil. In a Maple Grove or Woodbury walkout it is the walkout level. Getting this wrong is the most common reason a result is questioned later, and it is why we ask about the layout on the phone before booking.

Licensed Testing Under Minnesota Law

Minnesota's Radon Licensing Act requires anyone who tests or mitigates radon in a building they do not own to be licensed by the Minnesota Department of Health, and the register is public. A licensed test follows a written protocol for placement, duration and conditions, which is what lets a result stand up in a home sale. It is also worth checking whoever you hire against that register — including us.

After the Result

A low result ends the visit: we say so, and the advice is to retest every couple of years and after work that changes the house. A high result means the same visit has already told us most of what is needed to price a mitigation system — the foundation type, where the sump basket and floor drains are, which pipe routes will stay warm in winter. If there is a purchase agreement involved, testing inside an inspection period is scheduled around that date first.

How long does it take? Forty-eight hours of measurement, plus the twelve hours of closed-house conditions before it starts. Placement takes about fifteen minutes and pickup about the same.

Questions People Ask First