Process & access
Sometimes a system is so neglected that a standard clean cannot get it to the fifty-micron mark. That is not the end of the road - but it changes what the job involves, and what honesty requires.
The short answer
Occasionally a system has been left so long that a routine clean will not bring it back to standard. The grease has baked into a hard, carbonised layer; the ductwork may be corroded or damaged; and however good the crew, the surfaces will not reach the below-fifty-micron mark with a normal pass. This is not common, and it is rarely truly hopeless - but it does change what the job involves. What a good contractor does at that point is assess honestly and set out the real options, rather than either giving up or quietly signing off a system that has not actually been cleaned.
First, work out how far gone it really is
The starting point is a proper survey to distinguish a heavily greased system from a genuinely failed one. A lot of ductwork that looks beyond saving is simply very dirty - thick, baked grease that an intensive clean can still recover with more chemical dwell time, more hand scraping and more passes of the brush machine. That takes longer and costs more than a routine clean, but it gets a neglected system back to standard, and it is the right first answer for most 'too far gone' cases.
Some problems, though, are not about grease at all. Corrosion, split seams, fire damage or duct that was never properly accessible are structural, and no amount of cleaning fixes them. The survey - with camera inspection into the concealed runs - is what tells the two apart, so the plan matches the actual condition rather than assuming either that everything will clean up or that everything needs ripping out.
The real options
Where the issue is grease, the answer is an intensive clean, often combined with fitting proper access first so the worst areas can finally be reached and worked on. Missing access is frequently why a system got this bad - the concealed runs were never cleanable - so adding compliant panels is both the fix for now and the thing that keeps it maintainable in future. Once reachable and intensively cleaned, most neglected duct comes back to the fifty-micron standard.
Where the duct itself has failed - badly corroded, damaged or fire-affected - the honest answer can be to replace a section rather than pretend to clean it. And where, for whatever reason, part of the system genuinely cannot be brought to standard, a responsible contractor says so: the verification report and certificate record a partial clean, noting exactly what was and was not achieved. That honesty matters, because an insurer or fire risk assessor needs the true picture - a certificate claiming a full clean on a system that did not get one is worse than useless.
Neglect is recoverable, but only if it is faced honestly
A system that has been left too long is usually recoverable - with an intensive clean, added access, and section replacement only where the duct itself has failed. What matters is facing it honestly: assessing the real condition and reporting the true result, partial if that is what it is. That is what protects you, far more than a clean certificate that does not match the system.
Questions
Grease that has baked into a hard, carbonised layer, or ductwork that is corroded, damaged or fire-affected. In these cases a routine clean may not reach the below-fifty-micron standard on its own.
Usually, yes. Most systems that look beyond saving are simply very dirty and can be brought back with an intensive clean - more chemical dwell time, hand scraping and brush passes - often after fitting proper access.
When the problem is structural rather than grease - corrosion, split seams or fire damage. No amount of cleaning fixes failed duct, so replacing the section is the honest answer.
A responsible contractor records it as a partial clean, noting exactly what was and was not achieved. Insurers and fire risk assessors need the true picture, not a certificate that overstates the result.
Often because access was missing, so the concealed runs were never cleanable. Adding compliant panels fixes that and keeps the system maintainable in future.
Phoenix Duct Clean · by the numbers
We assess neglected systems honestly - what an intensive clean can recover, what needs added access, and where a section is best replaced - and report the result as it really is.