What are air ducts?
Air ducts are a vital component of a domestic air conditioning system (HVAC). They transfer the air between the air conditioning unit and the rest of the house. The ducts can be the hard type, usually made from sheet aluminium and shaped into rectangular or cylinder shaped sections bolted together or the soft flexible type made from plastic or foil.
Why clean the air ducts?
Air ducts require cleaning now and again to remove a build-up of bacteria, dust and mould spores. Usually the system’s filters make sure that particulates removed from the air do not find their way back into your home, but if these filters become overloaded and the ducts become choked then the properly designed air flowrates are not maintained and the particulate removal system becomes inefficient. The US Environmental Protection Agency (EPA) states that there is no evidence that requires the ducts to be regularly cleaned. They do, however state that if there is a specific reason then cleaning can be beneficial. We will go into these reasons later. Likewise some HVAC contractors also state that regular cleaning is a waste of time and money. Some allergy sufferers, however, have stated that when they have had their ducts cleaned regularly they suffer reduced symptoms and have cleaner air. These contrasting opinions mean that you must make up your own mind as to whether you have the ducts cleaned regularly without a specific reason.
All parties agree however that you should have your air ducts cleaned if you have a specific reason such as:
- Visible mould growth on any of your HVAC system’s components.
- Pest infestation such as rodents or insects, in your ducting.
- Excessive amounts of household dust blocking the HVAC ducting circuit, and releasing dust into the home when the system is turned on.
What does duct cleaning entail?
If you have the hard type of ducting then it can be cleaned using brushes to dislodge mould and damp, caked on dust. Brushes are not advised for the soft ducting however as the scraping could tear holes in the soft foil or dislodge joints. In this case, solvent sprays are recommended. Remember too that duct cleaning does not just involve cleaning the air channels, do not neglect the whole system’s regular check-up to keep the system running efficiently.
The normal HVAC system requires the use of a partial vacuum to suck loosened particles out of the system and a physical object to dislodge the build-up of accumulated debris. Together these two methods will clean ‘hard’ type ducting. Once all the solids have been removed the next step (which would be classed as an extra service and priced accordingly) would be to spray a chemical disinfectant to kill any micro-organisms such as viruses, bacteria or fungi left behind on the surfaces. This should only be done if it is proved that there is a biological hazard present to justify the use of a biocide. It is imperative that any microbial chemicals must be registered with the US Environmental Protection Agency specifically for use with HVAC cleaning methods.
How often should they be cleaned?
Although there is a dispute over how regularly the ducts should be cleaned, all bodies agree that routine maintenance should be done by qualified air ducts contractors every few years and as regularly as needed to maintain the efficient running of the system.
The National Air Duct Cleaners Association (NADCA) suggests that the user should consider the following when making a decision to have their ducts cleaned:
- How many smokers (if any) are in the building?
- Have you any pet animals that shed hair or skin?
- Whether the home or HVAC system has suffered water damage or contamination.
- Whether there are any asthmatics or other allergy sufferers who might benefit from regular cleaning.
- Have you had any house renovations done recently?
- Before you occupy a new home.
- How do I choose a good HVAC air duct cleaning contractor?
As with choosing any contractor to do work on your property it is imperative to select a qualified, experienced and registered contractor. Air duct cleaning is no exception. The following points can be used as a checklist to ensure you have done all you possibly can to hire a reputable company:
1. Make a list of as many contractors as you can.
2. Check to see if the company is a member of NADCA and is certified to carry out HVAC duct cleaning activities.
3. Download the ‘Homeowner’s Guide to Air Duct Cleaning’ from the NADCA website.
4. Find out how long the company has been in business. Is it long enough to get experience in this field?
5. Ask the contractor for proof that they are licensed and hold adequate insurance.
6. Ask them to visit your home and perform an inspection on your system to assess and explain the service they plan to provide.
7. Ask them to provide a quotation for the work.
8. Ask them to specify exactly what they are quoting for. Make sure they will be visually inspecting and cleaning all duct surfaces and related system components.
9. Get them to specify which components will be cleaned as part of their service. These could be the supply and return air ducts, coils drains, grills, and registers.
10. Ask if the company has the correct equipment to do the job and if they have previously worked in homes like yours. Make sure they will use both agitation and vacuum collection methods.
11. Make certain they will limit the release of dust and debris into your home during the clean.
12. If any chemicals are intended to be used in the cleaning process, ask them to list the names and provide safety data sheets for all chemicals. They must also justify the use of any biocide and only use those chemicals approved by the EPA for use in HVAC air ducts.
13. Ask them for a list of references and contact a random sample to find out their experiences with the contractor.
14. Avoid adverts for cut price deals and similar sales gimmicks.
What equipment will a contractor use?
A vacuum collector is one of the main pieces of equipment likely to be used. There are two types available for the contractor and the NADCA does not specify any preference of one over the other. The two types of vacuum units are:
Portable units. These are less powerful than the trailer mounted units but can be brought into the building and positioned close to the ductwork being cleaned.
Truck or trailer mounted units. These are generally more powerful than portable units and can only be positioned outside the house.
Both types will clean to ACR (the NADCA Standard). Both types will be connected to a collection receptacle to collect all solids and keep them contained until disposal. Any collection device which has an exhaust to indoors must have an adequate HEPA filter to prevent dust from being reintroduced into the house.
Agitation devices which are used in conjunction with the vacuum collector are designed to loosen the solids to enable the vacuum to transport them to the collection receptacle. Examples of agitation devices are:
Brushes. These vary depending on the proposed use and come in a variety of shapes and sizes. The brush will be soft bristled and will have a long handle to allow access to tight areas. Brushes are commonly used to remove stains on metal and fibreglass ducts.
Air whips. These are flexible pipes which deliver compressed air jets to areas around corners and in recesses. They are particularly useful for dislodging insects that have made nests inside your ductwork. Air whips come preassembled in lengths of 20 and 30 feet with various head attachments to provide different types of compressed air jets.
Skipper balls. These are ball shaped objects, made from metal or plastic that fit onto the end of a hollow rod which is connected to a compressed air supply. The ball has a series of small holes around its circumference allowing high pressure air to escape and loosen the solids. Sometimes the ball spins to allow the air jets to have contact with all parts of the duct.
Chemicals used to kill microbes in HVAC systems can be separated into the following categories:
Antimicrobial pesticide. This is any chemical substance that is designed to prevent, destroy or repel a microorganism such as bacteria, viruses or fungi. All pesticides must be registered with the EPA as well as with the State and approved for use with your application.
Sanitiser. This is a substance that kills a high percentage of bacteria on a surface. It does not necessarily kill all the bacteria present.
Disinfectant. This is a substance that kills a specific species of infectious or undesirable microorganism.
Fungicide. This is a substance that kills yeast, fungi and fungal spores that may cause a threat to human health.
Fungistat. Used to control the growth of fungi not regarded as dangerous to human health.
Bacteriostat. Used to control bacteria not regarded as dangerous to human health.
Algaestat. Used to control algae not regarded as dangerous to human health.
At the time of writing this article the EPA have only accepted the following for use in HVAC ductwork:
- Chemicals which inhibit odour causing fungi and bacteria.
- Chemicals which inhibit stain causing fungi, bacteria and algae.
- Cleaning chemicals such as soaps, detergents and degreasers.
The other categories of chemicals are only available for treating components of the HVAC system other than air ducts.
If in doubt, you should read the label on the original packaging and its MSDS document. All substances approved by the EPA will have that fact stated on the label and will also have the specific instructions for its use and application. It is an offence to use the substance in any way inconsistent with the information supplied on its label. All chemical substances must be kept and stored in its original container and used in a well ventilated area.
At present the chemicals registered by the EPA are only suitable for use on the smooth non-porous surfaces of sheet metal. There are no products authorised for use on fibreglass lining or fibreglass duct board. Therefore it is essential to determine whether your system contains fibreglass before the application of chemicals. If fibreglass air duct is contaminated then it must be removed and replaced with new.
If your ductwork is of the hard sheet metal variety, and if the contractor wants to use chemical biocides in the ducts, make sure that the contractor can show you evidence of microbial growth. Only lab analysis can determine whether there is microbial growth, so do not take the contractor’s word for it.
If there is evidence and you permit the use of a biocide, ask to see the original label and the chemical’s MSDS document. This will show the approved uses of the chemical. The application of the chemical biocide is not a substitute for physical cleaning and removal of dirt. You should only apply the biocide when all trace of dirt has been removed. Normally the house must be vacated when biocides are used because of toxic fumes however some substances of low toxicity may be legally applied when the house is occupied. Even so you may wish to vacate the premises while the low toxic biocide is being used.
How am I likely to know if the contractor has done a good job?
The only way to check if a contractor has done a good job in cleaning your air ducts is to do a thorough visual inspection. This may sound like a daunting task but it is the only way. Some good contractors will take remote photographs before and after doing the work, building up a record of all the work done. They will then produce a report for the customer with proof of work performed and may use the information in future training sessions for themselves. If the contractor does not take photographs then ask them to show you each system component to prove the job has been done.
How to avoid air duct cleaning scams
If you hire someone to decorate your house or tend your garden it is quite easy to see if they have done a good job or not. It is not so easy with HVAC duct cleaning contractor. An unscrupulous HVAC company may try to fool you with the following.
- Not having the proper equipment to do the job thoroughly.
- May leave the ducts dirty. They may only clean the parts you can see.
- May overcharge you for the work done.
- They may perform the minimum amount of work required and offer you upgrades to the service for additional costs.
- May damage your HVAC system.
- Might try to use a chemical not authorised for use on HVAC air ducting (see previous section).
The trouble is that you may never realise how much damage has been done until it is too late and the disreputable contractor has disappeared.
A disreputable company may offer a free mould “inspection” but will always find evidence of contamination resulting in greatly inflated costs “to have the mould eradicated”. This will happen even if your system was initially clear of mould.
Companies may also tempt you to hire them by offering low prices and then add on extra charges to the final bill.
Always suspect those companies who offer reduced prices or special offer deals. To clean HVAC ducting correctly is a very difficult and skilled job so good air duct contractors will charge you the correct price for a thorough job even though the cost may seem high.
Check with your local authorities to see if the company is registered, make sure the company publishes their address and visit them if possible; contact the National Air Duct Cleaners Association to find out if they are certified.
What costs are we talking about?
The NADCA has approved standards that dictate what is involved in a duct cleaning session. A proper clean does not just sweep the ducts but involves the inspection of every component affected by the air stream to see if clogging is taking place. This work needs at least two technicians for several hours and uses specialist equipment.
Because of the specialist nature of this kind of work you can expect to pay somewhere between $300 and $500 at the lower end and up to $1000 and above at the higher end. This price will always depend on:
- The size of your HVAC system.
- Accessibility of your HVAC system and ducting.
- Your climate type.
- Level of dust, fungi or microbial contamination.
- Duct material.
- Whether any lab analysis is required for microbial evidence.
- The application of EPA approved chemicals.
There are various safety regulations which must be adhered to when cleaning HVAC ducts. The areas covered by the regulations are as follows:
Access. Usually duct vents, through which cleaning equipment can access the ductwork, are high up a wall in inaccessible places. Ladders and scaffolding may be required for the technician to gain access to these vents. Working at height is inherently dangerous as even a fall of a few feet could have fatal consequences. It is therefore essential that technicians are suitably trained in working at height and are able to erect, dismantle and move their access platforms. Contractors might insist on the use of harnesses for their employees if access is particularly difficult. Protective helmets known as ‘hard hats’ should be worn as there is a risk of injuring the skull when in a confined area.
Working with chemicals. Suitable protective clothing such as coveralls, gloves, safety splash spectacles and breathing equipment will be required to prevent inhalation and skin contact with potentially harmful chemicals. Ventilation of the work area will also be required. A document known as a Material Safety Data Sheet or MSDS will be needed detailing the name, properties and hazards of the chemicals. The MSDS will also detail what must be done in the event of inhalation, ingestion or skin contact (particularly eye contact). A risk assessment will also have been done by the company stating how the chemical will be used and what has been put in place to reduce the risk to the operator and the householder.
Compressed air. Surprisingly compressed air can be dangerous. If a jet of compressed air comes into contact with the skin or the eye, the pressure can force the air through the skin barrier and into the blood. Bubbles of air in the blood can be fatal. Compressed air can force minute particles of grit or metal swarf into the eye, permanently damaging a person’s sight. Body covering clothing, protective gloves and safety spectacles will help prevent damage to the technician from compressed air.
Are there any tasks I can do myself?
You can’t really clean the ducting yourself. The operation requires special knowledge, training and equipment which would make it uneconomic to do so. There are however some things you can do. Irrespective of whether you call a contractor to clean your duct or not, it is always a good idea to set up a preventative maintenance programme to minimise contamination in your HVAC air ducts.
- First and foremost it is important that dirt doesn’t get into the system.
- Use a good filter that the HVAC manufactures has recommended.
- Change all filters at regular intervals.
- In case the filters are becoming clogged then change those more frequently and try to find out where the excessive dust is coming from.
- Ensure all filters are present and there are no spaces on the edges, allowing unfiltered air to bypass the filters.
- When you are having other parts of your HVAC system maintained, ask the contractor to check pands and cooling coils for dirt.
- If you are having construction or renovation work being done, do not operate the HVAC system until all work has finished and all dirt has been cleaned up.
- Clean your house with a vacuum cleaner regularly and only use one fitted with a HEPA filter to prevent dust being blown into the air from the cleaner’s exhaust.
- Prevent the ducts from collecting moisture by regulating the humidity in your home; repairing any water leaks or damage; ensure ducts are sealed and insulated in attics and similar non-air conditioned places.
To prevent the need for air conditioning ducts to be cleaned in the first place always keep the air filters in top condition and ensure no moisture is allowed to build up within the system. Using a preventative maintenance programme is the way to do this and will save you money in the long term.
If you decide to have your air ducts cleaned, using the correct equipment is the key to cleaning the surfaces efficiently. Delivering compressed air to the area needing to be cleaned together with an agitation device is usually the only way to dislodge caked on dirt.
Only use those chemicals approved by EPA for use within air conditioning ducts. For you to use, or allow anyone else to use any other chemical is a criminal offence.
Remember that the application of a chemical biocide is not an alternative to physically cleaning an air duct surface. It is always an extra and should only be done if evidence of microbial growth has been proved by an independent laboratory analysis.
Watch out for unscrupulous contractors who are not certified, registered or trained, and don’t end up paying more than you have to.