Field Experiences with Air Filtration: Results and Costs

Air filtration systems have been in place for over three years, in a wide variety of farms, and are valuable in reducing the risks of PRRS, according to Darwin L. Reicks, DVM, of the Swine Vet Center in St Peter, Minnesota. His article was in the January 2009 issue of North Carolina Extension Swine News.
calendar icon 1 June 2009
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It has been over three years now since the author installed air filtration into the first farms in his practice. They now have 25 farms with air filtration. Six farms implemented filtration in 2005, five in 2006, eight in 2007, and six so far this year. Application of filtration systems in the practice has been previously described [1,2,3,4] so the author reviews what has been learned from these experiences.

Filtration System Options

There is no “one size fits all” to air filtration. It has been necessary to work up each farm on a situation-by-situation basis. All of the farms have utilised Merv 16 Camfil Farr filters to date. Some of the new filters have been used from Camfil Farr, called the PB L6 filter. There are 17 boar studs, six sow farms, one finishing site and one research barn, small and large. Three of the sow farms have 2,500 sows. The other three have 500-1200 sows. Five of the boar studs are air-conditioned.

The current breakdown of types of filtration are 15 with 100 per cent filtration and 10 have some sort of partial filtration system or bail out system, where air is 100 per cent filtered at lower temperatures but as the ventilation system needs to move more air (typically 70-80 degrees F outside temperature), the air comes into the barn unfiltered.

For the Camfil Farr Merv 16 filter, now revamped to the PB L9 filter, it was estimated 600 cfm of air will go through the filter at 0.2 inches W.G. For the PB L6 filter, 1000 cfm of air is estimated to go through the filter at 0.2 inches W.G.5 Most of the sites have been able to run the static pressure to 0.2 without any trouble, although it is important to know which fans you have and how they perform at these higher loads [6].


An important consideration from the start has been not to expect never having a PRRS break just because of the air filtration. However, if the incidence of PRRS breaks can be reduced significantly, it would be a good return on the investment. This has proven to be the case. Most of the farms that have filtration had a previous history of PRRS breaks. Since implementation of air filtration, there have been three PRRS breaks on farms using partial filtration. All three were infected when the air was not being filtered. There was one PRRS break on a 100 per cent filtered farm, although filters were found to be damages and there was another possible route of virus into the farm via trucking. There have been two Swine Influenza breaks on 100 per cent filtered farms, but no Mycoplasma hyopneumoniae breaks on any of the filtered farms, although most are vaccinated.

Filter Options

There have been many enquiries from producers about cheaper filters. Not all filters are equal and the current rating systems are not necessarily applicable to what we are doing. For example, the barns are run typically at 0.05 to 0.20 (inches W.G.) for static pressure. When these types of filters are tested, they are done so at much higher pressures. As a result, quality of materials, frame integrity, etc. become much more important to make sure no air can bypass the filter material itself.

There has been some redesign of the frame and also a new filter that has better air flow but may have a breaking point and allow virus to pass through at very high concentrations. The strategy right now is to use the same filter as in the past (now called L9 filter since the new frame design) for farms that have a poor history with PRRS, have farms within about two miles, or have a large number of pigs within three or four miles. The higher air flow filter will be used for lower risk farms.

Partial filtration continues to be utilised due to cost. The problem is with just putting filters on the ceiling inlets and having no filtration for cool cell pads, most of those farms are unfiltered for about four months of the year. One farm switched from partial filtration to 100 per cent filtration just by switching the filter bank to the new higher airflow L6 filter.

Trouble-Shooting and Challenges

A number of things have been learned in the last three years:

  • Partial filtration – not good enough to only filter ceiling inlets in hog-dense areas.
  • Air restriction of the filter – the new filter will help but for high risk farms, there really does not appear to be an answer other than you just have to have lots of filters.
  • Air locks – for any doors where animals go out or in, dead or alive, we have put air locks in place.
  • Back-draughting through non-operating fans – positive pressure reduces this risk but can be hard on buildings when pushing cold air in the winter. For the negative pressure barns, the fan covers are left on as long as possible and in some cases, put back on if risky weather conditions are approaching.
  • Proper installation of filters – a third party inspects the installation – often the installers have a ‘good enough’ approach. Air conditioning experts and ventilation people are not used to having to have 100 per cent seal on duct work or inlets.
  • Damage on installation – a number of the sites have had filters damaged during installation – important to have the third party inspection. No one wants to be blamed for damaging expensive filters. The best approach has been education up front to make sure they do not handle the filter material itself.
  • Changing of pre-filters – it has been tried changing every six months but sometimes people forget – it is important to change every six months or at least inspect. This is a good time to look for air leaks or damage to the more expensive filter underneath.


Because there are different building designs and different applications of filtration, there are different costs. In summary, this is what is required to implement air filtration systems.

  • Partial filtration. For farms that have tunnel ventilation in the summer and just put filters on ceiling inlets, the cost per sow or boar has been about $35 to $40 per animal. As mentioned previously, we have only been able to filter up to about 70 degrees F with these types of systems and typically around 80 cfm per animal in a boar stud or gestation barn. The estimated cost is $0.70 to 0.80 per weaned pig over 10 years including filter replacement and associated labour.

    For the bail-out farms, it really depends at what temperature the farm bails out of the filtration system.

    For the wean-finish site, it is estimated at $1.70 per marketed pig. This system currently has filtration capacity up to about 40 cfm per pig.

  • 100 per cent filtration. Air conditioning – there are five air conditioned boar studs in the practice. The cost of the air conditioning system with 100 per cent filtration is $350 to $500 per animal.

    For barns where all the air goes through a cool cell, up into the attic, then down through ceiling inlets, the cost has been around $85 per sow or boar, or around $1.50 per weaned pig over 10 years.

    For barns that have air come through ceiling inlets in the winter, then switch to tunnel ventilation for the summer, the cost has been $185 to $200 per sow or boar. The reason for the extra cost is filter banks need to be constructed in front of each cool cell pad so there is extra construction cost. Also, more filters are needed overall as one has to cover both the winter and summer ventilation scenarios independently. The cost estimate for these sites is around $2.40 per pig over 10 years.


Air filtration systems have been in place in the practice for over three years, in a wide variety of farms, both large and small. For boar studs, filtration has become the standard, except for studs with no history of PRRS and located five miles or more from other pigs. For sow farms, cost range from $1.50 to $2.40 per weaned pig. The cost of a PRRS break has been shown to easily exceed this. As a result we expect the application of filtration to continue.


  1. Reicks, D.L. 2006. Alternative filters for boars. Proceedings from the 2006 Allen D. Leman Swine Conference, 99–100.
  2. Reicks, D.L. 2007. Field experiences with air filtration. Allen D. Leman Swine Conference: Carlos Pijoan International Symposium on Swine Disease Eradication, 23–26.
  3. Feder, J. 2008. Experiences in sow farm filtration. American Association of Swine Veterinarians Meeting. Filtration pre-conference proceedings. 15–16.
  4. Reicks, D.L. 2008. Filtration and air conditioning. American Association of Swine Veterinarians Meeting. Filtration pre-conference proceedings. 17–18.
  5. Camfil Farr technical literature. 2008. Personal communication.
  6. Brumm, M. 2008. Fundamentals of air flow. American Association of Swine Veterinarians Meeting. Filtration pre-conference proceedings. 1–6.

Further Reading

- Find out more information on porcine reproductive respiratory syndrome (PRRS) by clicking here.

June 2009

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