Professional Tests vs. DIY Kits: Which Do You Actually Need?
For a first look at a home you already own with no deadline attached, a DIY kit is genuinely fine — and around here it's often free. For a real-estate transaction, a disputed result, or a decision you're about to spend $1,500–$3,000 on, a professional continuous-monitor test is the right tool.
A charcoal kit gives you one averaged number for the test window. A continuous radon monitor (CRM) records levels hour by hour, which is why professionals use it: it shows whether your radon holds steady at 5, or lives at 2 and spikes to 12 overnight when the house buttons up. It also timestamps the data, so if a door was propped open halfway through a real-estate test, the record shows it. Professional tests in Colorado typically run $125–$400; DIY kits are $10–$30 retail, and continuous monitors you can buy yourself run about $150–$230.
First, the Free Options — Seriously
Before you pay anyone, including us: every county in this valley gives away radon test kits, and if a free kit answers your question, use it. We'd rather you test free and call us only if the number is high.
- City of Aspen: free kits year-round at Community Development, first floor of City Hall, 427 Rio Grande Place — or reach them at airquality@aspen.gov / 970-920-5039.
- Pitkin County: free kits every January at 530 E Main St, Suite 205. The county also publishes public dot-maps of valley test results.
- Garfield County: free kits year-round in Glenwood Springs (2014 Blake Ave), Rifle, and through CLEER at the Third Street Center in Carbondale; kits can even be mailed — 970-665-6383.
- Eagle County (Basalt/El Jebel side): free kits at locations including the El Jebel Community Center, limit two per household per year.
- CDPHE (statewide): one free kit per household per year.
Where a paid test earns its fee: transactions on a deadline, results near the action level, conflicting numbers, verifying a mitigation system, or any situation where an hour-by-hour record matters more than a single average.
The Closed-House Protocol: Why 12 Hours Matters
Every short-term radon test — free kit or $400 professional CRM — requires windows and exterior doors closed for 12 hours before the test starts and for its entire duration. This is the EPA's closed-house protocol, and skipping it is the single most common way valley homes get a falsely low result.
The 12-hour figure isn't arbitrary. Radon has a half-life of 3.8 days, and indoor levels reach steady state roughly 12 hours after a home is closed up. Air the house out the morning of your test and you're measuring fresh mountain air, not your home. This is especially common with second homes here: a caretaker opens everything up before guests arrive, someone drops a kit on the counter, and the "reassuring" result is meaningless. Normal coming and going through doors is fine — it's open windows and whole-house airing that invalidate the test.
Winter Is the Worst Case — So Winter Is When to Test
Radon peaks in winter, which means a winter test measures your real exposure and a July test measures your best case. Three things stack up in a Roaring Fork Valley winter: frozen, snow-covered ground blocks soil gas from venting outdoors, so more of it follows the path of least resistance — under your slab. Your sealed, heated house creates the stack effect: warm air rising and escaping up high pulls replacement air in down low, straight from the soil. And the heating season here runs seven-plus months, so this isn't a brief seasonal blip — it's most of the year. Both the City of Aspen and the state health department recommend testing in winter for exactly this reason. If your only data point is a summer reading of 3.2, treat it as a floor, not an answer.