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Break Down The Standard: IRHACE HVAC Hygiene Best Practise Guideline March 11, 2020

Presco Environmental technician, Frank, changing filters in HVAC room.


The IRHACE HVAC Hygiene Best Practise Guideline is one of two documents that are vital for any plant manager in a food factory to know.  

Let us break it down for you below.   

According to IRHACE, unhygienic HVAC systems can cause:

  • Greater health risk
  • More complaints from occupants
  • Higher fire risk
  • Inefficient system performance
  • Reduced productivity of people
  • Increased operating and maintenance costs
  • Greater risk to equipment and processes
  • Higher risk to building owners
Inside of Air Supply Ducting


To help regulate this in New Zealand, IRHACE modified a document made by AIRAH in Australia, and created their industry-developed HVAC hygiene guideline for New Zealand conditions.  Although this is not law, you would need to justify yourself should you suffer a food safety incident and had chosen not to follow it.  


The guideline provides valuable information to many parties; one being owners and managers of commercial buildings


Furthermore, it defines any facility involved in the production of food products as a ‘Special Use System’. 


The following article provides a summary of the ‘why, how and when’ of maintaining acceptable hygiene levels in your Special Use HVAC system. 



Minimum Inspection Intervals

IRHACE recommends you inspect each component at least this often:


HVAC System Components

Minimum Inspection Intervals

Air handling units


Supply system – moisture producing equipment


Air intakes and exhaust outlets


Supply air systems


Return air systems


Outside air systems


Exhaust air systems


Evaporative coolers


Non-ducted air conditioning



These inspections should be checking for:

  • General dust
  • Biological contamination
  • Fungal contamination
  • Asbestos
  • Deterioration of non-porous surface
  • Deterioration of porous surface
  • Water damage
  • Fire and smoke damage
  • Building or renovation contamination
  • Odours
  • Damage to the actual HVAC system
  • Hazardous contaminants


Air filter being cleaned of biological contamination


When referring to biological contamination, IRHACE mentions screens covering air intake and discharge are necessary to prevent pests, contamination and moisture from entering. 


These inspections are checking to see if the system or components meet the minimum hygiene level.  If they do not, they should be cleaned. 


You need to present the findings of these inspections in a clear and concise audit report.


Minimum Hygiene Levels


  • Air handling units
  • Supply system – moisture producing equipment
  • Air intakes and exhaust outlets
  • Non-ducted refrigerated a/c
  • Evaporative coolers
  • Post-filtration of your supply air, return air and outside air systems


  • Pre-filtration of your supply air, return air and outside air systems


  • Exhaust air system


Unsure what these levels actually mean?  IRHACE kindly defined each of them and provided us with visual guides. 



Clean level of hygiene as defined by IRHACE HVAC Best-practise Guideline

No visible dust, debris or contamination. 


Light level of hygiene as defined by IRHACE HVAC Best-practise Guideline

Slightly visible layer of dust dispersed evenly throughout, but light enough that you can still see the surface underneath. 


Moderate level of hygiene as defined by IRHACE HVAC Best-practise Guideline

Visible dust layer with more dense sections, and a limited gathering of fine debris.  Surface shall still be visible under the dust, but you may not be able to see it in all areas. 


Heavy level of hygiene as defined by IRHACE HVAC Best-practise Guideline

This level of hygiene is never acceptable in an HVAC system. 


Post-clean Hygiene Verification

After cleaning, the hygiene of each component needs to be verified before operation can resume. 


IRHACE suggests five methods of hygiene verification:

  1. Visual inspection
  2. Surface comparison testing
  3. Vacuum test
  4. Coil verification test
  5. Fungal decontamination verification


This verification needs to be presented in a hygiene verification report


Working with a Specialist Service Provider

This guideline has an entire section dedicated to helping managers working with a specialist service provider. 


When selecting a service provider, IRHACE suggest checking they:

  • Understand and comply with this guideline
  • Have an appropriate level of resource to suit your need
  • Have evidence of experience, training and previous work
  • Have appropriate insurance and licenses
  • Have an informative reporting system
  • Have quality, environmental and safety systems in place.


If creating a contract, IRHACE recommends the contract includes:

  • A description of the system and components that will be cleaned
  • The full extent of any contractor guarantees
  • Date, time periods and terms of payment
  • Responsibilities of parties
  • Insurance requirements
  • Details of any sub-contractors
  • Reporting and verification arrangements
  • Photos of specific areas to be treated
  • Site availability for cleaning (days and work hours)
  • The scope of work (needs to clearly state the services to be provided)


The contractor also needs to provide the additional information:

  • Site specific project management plan including strategies
  • Cleaning methods – ductwork, coils, fans, pans and drains
  • SDS of chemicals to be used
  • Disposal of handling strategies for any removed contaminants
  • Odour management
  • Noise control
  • Verification protocol


Presco Environmental technicians filling out job information reports for the customer.


Your Responsibilities as a Manager

Lastly, IRHACE gives a thorough list of your responsibilities as a manager.  You should:

  • Provide appropriate access to the site
  • Give accurate system operating and maintenance information
  • Provide ‘as installed’ system construction drawings
  • Provide power, water and drainage
  • Provide additional heating, cooling and ventilation if the usual systems are not working
  • Participate in cleaning verification protocols
  • Inform occupants and emphasise the benefits of the investment
  • Communicate between parties

IRHACE has been a great help to us all by providing this comprehensive guideline so that we can achieve ASNZ3666

We have attempted to pick out the most important bits of the document so that you can get your head around all you need to know, without drowning in the mass of jargon that standards are notorious for. 

However, this is by no means conclusive; the actual IRHACE HVAC Best Practise Guideline is a truly informative document, and well worth the read.  Contact IRHACE and you can purchase your own copy for $20.00.

As mentioned at the beginning, the IRHACE HVAC Hygiene Best Practise Guideline is only one of two vital documents for you to understand.  Read our breakdown on the ASNZ3666.2 Standard here.  

If you have any questions on this guideline, please ask below. 

Presco Environmental are able to set up and execute IRHACE compliant HVAC Hygiene maintenance programs. For more information on this, please contact the author.

Matthew Prestidge, General Manager

About the Author

Matthew Prestidge is our General Manager and Senior Industrial Hygiene and Indoor Air Quality advisor.

Having spent the last 15 years creating more sustainable environments on industrial sites, Matthew has seen the good, the bad and the ugly and knows what is required to “clean up”.   

Would you like to discuss solutions to industrial cleaning issues?  
Matthew offers a free consultation and easy-to-implement advice on Industrial Hygiene and Indoor Air Quality for anyone in the New Zealand Food and Beverage industry. Contact him at matthew@presco.co.nz 



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