Durridge’s RAD8 and RAD7 Calibration Services includes a comprehensive range of tests, routine maintenance, and adjustment of any parameters necessary to bring your instrument up to full specifications, as well as replacement, if needed, of consumable components such as the battery and NVRAM chip, and up to a half hour of labor for any additional minor repairs.

A signed Calibration Certificate is sent with every new RAD8 and RAD7 that we ship, and an updated certificate is provided every time an instrument is sent in for calibration.

For an additional fee, Durridge will conduct an As Received Precise Calibration, which determines the existing sensitivity of your instrument before it is serviced and recalibrated. The calculated pre-calibration sensitivity values can be applied to radon data that was recorded earlier, in order to correct for any sensitivity drift that occurred while the instrument was in service.

Durridge’s radon calibration facilities in the USA and the UK have their own controlled, standard source of radon gas. All RAD8 and RAD7 testing, calibration, and quality assurance is performed at Durridge by NRSB-certified, Durridge-qualified staff.

The Durridge calibration system is compared, to a precision of better than 1%, with a secondary standard chamber, which is in turn calibrated by comparison with a NIST radon standard supplied through the U.S. EPA. The Durridge system accuracy is also independently checked by making a direct determination of the system radon level from the activity and emission of our European standard radon source. Our Calibration Service achieves a reproducibility of better than ±2% and an overall calibration accuracy of better than ±5%. (Ever vigilant, we also compare our instruments with other radon measurement devices through periodic participation in inter-comparison workshops held worldwide.)

The U.S. EPA recommends that continuous radon monitors, such as the RAD8 and RAD7, be calibrated at least once per year, and Durridge agrees.

The price of RAD8 and RAD7 Calibration, including comprehensive testing, routine maintenance, and (if needed) replacement of consumable components is $624.

Shipping Information

1. Before you send a RAD8 or RAD7 unit back to us, please complete the Instrument Return Form and email it to Durridge at . Include a printed copy of the form in the box with the device. You can send your shipment to either of our facilities (USA or UK), listed below (see important, specific instructions for each below).

2. We typically need the RAD8 or RAD7 in house for 10 business days, provided it has no serious problems. Once it has been serviced, the instrument will be shipped back to you after payment is received, so the total time the instrument will be away from your facility is typically 10 business days, plus the time it takes the receive the payment, plus the time the instrument spends in transit. If additional service or repair is required, this may delay the return of the instrument.

3. When sending your RAD8 or RAD7, please send the instrument only, without the cables and accessories. Pack the instrument upright in a box with one-inch (2.2cm) padding all around. A 14x14x14in (or 36x36x36cm) box is suitable. Pack the box well, and seal it carefully.

4. International customers must be very careful, to avoid substantial extra shipping charges and delays, both for shipping to the nearest calibration facility, and for its subsequent return.

5. Commercial Invoice check-list (for international shipping only):

  • For your courier or freight forwarder, you will need to provide a Commercial Invoice.
  • Please write only in English on the commercial invoice.
  • Use the following description for a RAD7: “Used RAD7 Electronic Radon Detector”. For a RAD8, use “Used RAD8 Electronic Radon Detector”.
  • Insured value US$1,500.
  • Please state on the invoice that the instrument is MADE IN USA and that it is being “returned to the manufacturer temporarily for repair and recalibration“.
  • Please use the HS (Commodity) code 9030.10.00.
  • Please mark the box with the serial number of the instrument (as the RMA – Return Merchandise Authorization).
  • Please add the phone number of the Calibration facility you choose, in case the Customs Office wants to call us.
  • Next, you must ensure that your courier (i.e. UPS, FedEX) or freight forwarder will deliver the package to our door. The formal “INCOTERM” for this is “DDP”, which means “Delivered Duty Paid.”
  • We will not pay or be responsible for USA or UK import duties, or Customs clearance charges. Your shipper must be told this when you arrange your shipment.
  • It is important to make sure you prepare all the documentation you need to reimport the goods back into your country without being charged.
  • For the Return to you: unless you instruct us otherwise, we will return your Durridge instrument via the same shipping method you used to deliver it to us, Freight Collect. DURRIDGE can pay for the return shipment CPT (“Carriage Paid To”) to you, but our cost will be invoiced to you before shipment.

If we can help further, please email us at

Specific info for SHIPPING TO OUR USA FACILITY (from outside the USA)

DURRIDGE Company, Inc.
900 Technology Park Drive
Billerica, MA 01821-2812, USA
Phone: +1 (978) 667-9556
Fax: +1 (978) 667-9557

Declaration Form

  • There needs to be documentation proving that the instrument was previously imported into your country, otherwise you may be charged import duties when the instrument is returned to your country.
  • Please fill out the declaration form provided below. Attach the completed declaration form to the commercial invoice. If the invoice is scanned and submitted electronically, please scan the declaration form and submit it electronically as well.

Foreign Shippers Declaration of US Goods Returned (PDF)


Sheffield Technology Park
Cooper Buildings
Arundel Street
Sheffield S1 2NS, UK
Phone: +44 (0)114 221 2003

Please complete the checklist in the above section. It is very important to include the HS (Commodity) code 9030.10.00, otherwise import duty may be charged at the UK border, for which you will be liable. Please also include our EORI number GB219670885000.

Please ensure that you make the necessary arrangements with the Customs authority in your territory for the return of your instruments. There may be special procedures for temporary exports. For example, you may need to provide documentary evidence that the instrument was previously imported into your country, to avoid being charged import duty again.

Calibration System Info

DURRIDGE Calibration System

DURRIDGE Calibration System

Durridge’s calibration system continuously monitors RAD8 and RAD7 performance in a controlled environment over a multi-day period.

DURRIDGE calibration technician

DURRIDGE calibration technician

Instrument Return Form

Fill out this form before returning a RAD8 or RAD7 to DURRIDGE for repair:
Instrument Return Form (PDF)