Radon
Does a radon sump and a fan mean the house is below the Action Level?
No. A sump and a fan are a common way of reducing radon. Seeing them means someone installed a system. It does not tell you the level now, whether the fan runs, or whether the level was ever measured. The Action Level is 200 Bq/m3 as an annual average from a proper test, not the presence of a plastic box and a switch.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Fans fail, get switched off, and get blocked. A home survey can note a fan if it is visible. It will not leave detectors for three months, and it will not service the fan. Ask the seller for any commissioning test and any later retest. A missing retest is a gap, not a pass and not a fail.
If you want to know whether the system is doing its job, measure. Do not deduct a new-fan price from the purchase without a quote from a firm that has seen this system. This page states no fan price. Do not confuse the £3.90 address-search fee with a replacement fan.
What should you ask your surveyor?
- Could you see a fan or a sump, and was it running?
- Is there any test result in the papers you were shown?
- Are you rating the fan, or only noting it exists?
What are the typical next steps?
- Ask for the original test and any retest in writing.
- Do not switch the system off to “see if it matters”.
- If there is no test, commission one rather than pricing a second system on guesswork.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
Is a fan in the cellar a bathroom extract?
Not necessarily. Ask what it serves. A bathroom fan does not reduce radon under the floor.
Does Approved Document C prove this fan was required?
Approved Document C signposts radon protection for certain new building work. It is not a test of an existing fan.