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Keywords: Air cleaner, Air filter, Air filtration, Breathing zone, CADR, Clean air delivery rate, Environmental control, Furnace filter, HEPA, HVAC, Indoor air, Indoor allergens, Intervention measures, Ozone, Particulate matter, PM, Room air cleaner, Sleep breathing zone, Ventilation, Whole house filtration

In the case of filtration, little attention has been paid to variations among the various appliances themselves, and no clinical comparisons have been done between the benefits of whole house filtration (WHF) versus those of portable room air cleaners (PRACs). According to the most recent American Housing Survey, 75% of US housing units have ducted forced air heat, while 63% have ducted central air conditioning [9]. When used in combination, these ducted heating systems are termed heating, ventilation, air conditioning (HVAC) systems. HVAC systems offer the opportunity for WHF, but poorly maintained or contaminated systems may actually increase the risk of asthma and other allergic respiratory symptoms [10]. Simple forgetfulness by the occupants in replacing the filter at suggested maintenance intervals may be the most common issue. HVAC service technicians frequently find round air filter that have not been changed for years when providing repair or maintenance services [11]. Dirty filters themselves can become a source for air contamination by allergens, particularly fungal spores [12], and can then be trapped, colonized, and released downstream as the overloaded filter fails [13]. Other issues, including air bypass from poor filter fit and duct leakage, may further confound the effectiveness of filtration in HVAC systems.In a 2010 rostrum article, Sublett et al. [22••] provided a comprehensive review of air filtration. The authors described the characteristics of airborne particulates, including allergens, to be filtered, and pointed out that the impact of inhalable PM and the effect on disease is not always IgE mediated. Residential air-cleaning products and devices are categorized into two broad categories: WHF (ie, filters or cleaners that are installed on the central HVAC system) and free-standing PRACs. Current standards for testing to determine the American Society of Heating, Refrigeration, and Air-Conditioning Engineer’s (ASHRAE) minimum efficiency rating value (MERV) for furnace filters and the Association of Home Appliance Manufacturers rating system clean air delivery rate (CADR) for room air cleaners are outlined. They also described the results of 18 studies on air filtration from 1973 to 2009, including some studies previously reviewed. The authors concluded that for the “optimal choice of cleaning devices, initial cost and ease of regular maintenance should be considered. PRACs with HEPA filters, especially those that air breather filter the breathing zone during sleep, appear to be beneficial. For the millions of households with forced air HVAC systems, regular maintenance schedules and the use of high-efficiency disposable filters appear to be the best choices.” They, as had previous reviewers, recommended that more rigorous study methods be applied to future research on air filtration and that the studies be of sufficient duration to show effectiveness.

The most effective ways to improve your indoor air are to reduce or remove the sources of pollutants and to ventilate with clean outdoor air. In addition, research shows that filtration can be an effective supplement to source control and ventilation. Using a portable air cleaner and/or upgrading the cone air filter in your furnace or central heating, ventilation, and air-conditioning (HVAC) system can help to improve indoor air quality. Portable air cleaners, also known as air purifiers or air sanitizers, are designed to filter the air in a single room or area. Central furnace or HVAC filters are designed to filter air throughout a home. Portable air cleaners and HVAC filters can reduce indoor air pollution; however, they cannot remove all pollutants from the air.

The following publications provide information on portable air cleaners and on HVAC and furnace filters commonly used in homes.

Heating ventilation and air conditioning system (HVAC) is very important for offices building and human health. The combining filter method was used to reduce the air pollution indoor such as that particulate matter and gases pollution that affected in health and productivity. Using license plate frame in industrial HVAC systems (factories and manufacturing process) does not enough to remove all the indoor pollution. The main objective of this study is to investigate the impact of combination filters for particle and gases removal efficiency. The combining method is by using two filters (particulate filter pre-filter and carbon filter) to reduce particle matter and gases respectively. The purpose of this study is to use minimum efficiency reporting value (MERV filter) rating 13 and activated carbon filter (ACF) to remove indoor air pollution and controlling the air change rate to enhance the air quality and energy saving. It was concluded that the combination filter showed good removal efficiency of particle up to 90.76% and 89.25% for PM10 and PM2.5 respectively. The pressure drop across the filters was small compared with the high-efficiency filters. The filtration efficiency of combination filters after three months' was better than efficiency by the new MERV filter alone.