But you don't have to hold your breath to make a positive impact on the environment.  The new facility at the Humane Society of Huron Valley (HSHV) in Michigan is slated for completion in July of next year.  Among other green measures, the organisation is installing an HVAC (heating, ventilation, and air conditioning) system that provides 10 air changes each hour.  The system simultaneously recovers the escaping energy through a device placed over the outdoor exhaust, letting the bad air out while keeping the heated or cooled air in.

"We have no ventilation right now, other than opening the window at the far side of the hall," says HSHV executive director Tanya Hilgendorf.  "We're really hoping that that clean, fresh air that the animals will be breathing in will reduce disease spread."  It's an innovative strategy that the shelter hopes will make for lower energy costs and healthier animals.

But according to Kate Hurley, D.V.M., director of the UC Davis Koret Shelter Medicine program, even the best HVAC system will be a waste of money if the basics in disease prevention aren't done first.  "If you invest in heating and cooling 11 air changes per hour, but you put your cats in small boxes that are closed on five out of six sides then you're not taking advantage of your investment," she says.  Hurley argues that if more preventative measures were taken such as allotting more space per animal, and thus needing to disinfect less often, shelters would require fewer air changes in the first place.

Hurley also suggests that shelters provide outdoor space for both cats and dogs.  Lack of outdoor space, Hurley says, is the main culprit for the prevalence of URI, which she estimates affects at least 30 percent of the cat population in the average shelter, and drives up costs in staff time and other resources the shelter must spend taking care of sick kitties.  "Shelters are a little reluctant to adopt outdoor space for cats, because they think it's going to be unnecessarily costly-but actually I think it could be very cost effective, and in fact, much cheaper."

Ventilation of kennels is important to reduce odour, provide clean air, and to reduce the concentration of airborne infectious agents.  Any type of ventilation where the airflow is not controlled directly, for example opening doors and windows, is referred to as Passive ventilation.  Passive ventilation is adequate for a small number of animals, but may result in unacceptable levels of heat loss.  Any type of ventilation where the airflow is controlled by specially designed blowers or extractor fans is known as Active ventilation.  

Active ventilation can be combined with heating (air conditioning), and is far more effective in larger establishments, affording a much higher degree of control.  Commonly used systems include air conditioning with induction vents and an extractor fan with passive vents.

The design of the ventilation system should be such that airflow between kennels is minimised to reduce the spread of diseases.  Ventilation must be provided to all interior areas without the creation of excessive, localised draughts in the sleeping area.

Heating can equally be removed by ventilation.  A balance is necessary between adequate ventilation and the unnecessary removal of warm air.  Ventilation is important as an aid to disease control, a protection against smell accumulation and prevents excessive humidity of the atmosphere.  High humidity increases the risk of kennel cough and should be avoided.

Hurley has been studying animal shelters in England, where cats are often given controlled access to the outdoors.  If American shelters were to follow their example, Hurley estimates that URI cases in American shelters could drop to one-tenth the current number.  In addition, she says, outdoor cat space is ideal for exercise and stress reduction, while providing better air quality, medically and emotionally beneficial sunlight exposure, and a means of interaction between potential adopters and cats.