For Merv 8, 11 and 13 filters, it is recommended that you change the filter at least every 3 months for optimal filtration and healthier air in your home.
Merv 13is the highest grade appropriate for residential heating and should be replaced every 9 to 12 months. If the filter usually lasts 90 days, it should be changed every 30 days during peak summer and winter months, when the HVAC systems are operating at their maximum capacity. Chemical disinfectants should not be applied to ventilation filters before continuing to use them within ventilation systems.
The effects of disinfectants on filter performance are unknown, so they should only be treated with disinfectants if they are to be removed from service and discarded. UV systems are quite effective in maintaining the cleanliness of HVAC coils, drain trays, and other wet surfaces. These systems generally require more lamps so that they can provide significant UV doses in a short period of time. A typical single-pass inactivation efficiency is 85%, much like that of a good particulate filter, but systems can also be designed for inactivation greater than 99.9%.
In addition, a well-designed UV air disinfection system within an air conditioning system and located next to the cooling coils can also provide surface disinfection benefits. Another way to install UV is in a “higher air” configuration. Specially designed wall-mounted devices create a radiated area above the occupant and disinfect the air in the space as the air circulates naturally, mechanically or through the air conditioning system. CDC has approved this type of system for use in tuberculosis control for nearly 20 years and there is guidance from NIOSH on how to design them.
Mobile UV systems are frequently used for terminal cleaning and surface disinfection in healthcare and other spaces. Systems like these are commonly used in unoccupied spaces due to concerns about occupant exposure. All three types of systems may be relevant, depending on the type of building and the individual spaces within the building. The design and sizing of effective ultraviolet disinfection systems can be a complex process because of the need to determine the dose administered to a moving air stream or to an irradiated region of a room.
Inlet systems are further complicated by the configuration of the air treatment unit and ducts and reflections from surfaces, which can help achieve higher levels of irradiation. Upper air systems require an adequate air mix to function properly and, at the same time, pay close attention to reflective surfaces that could cause room occupants to be overexposed to UV energy. Accredited system manufacturers and designers can help by making the necessary calculations and designing specific systems for individual spaces. Using an air filter with a MERV rating higher than recommended by the boiler or air conditioner manufacturer may affect its performance. Laboratory studies indicate that reaerosolization of viable mycobacteria, which are similar in size to that of viral particles, from filter material is unlikely under normal conditions. Similarly, a 1-inch pleated filter will need to be changed more frequently than a 4-inch pleated filter, which can last up to six months before it needs to be replaced because it has more area for particles to build up. A good oven filter can help you improve the air quality in your home, but a dirty air filter will do the opposite.
A larger home generally requires more frequent filter changes because ovens and air conditioners must release more air for temperature fluctuations. The only type of filters that trap allergens and spores are HEPA, or high-energy particulate air filters. Specifically, to obtain high MERV ratings and greater thickness, these filters easily require only two filter changes per year. For a residential filter in a slot that is a little loose, you can use a simple piece of tape, hold it in place and allow air flow to push the filter forward to attach to the flat surface in front. A dirty air filter restricts air flow, leading to poor air quality, higher energy bills and, over time, causing the system to eventually fail. Filters with higher MERV values trap small particles more effectively than filters with lower MERV scores.
As a general rule, you'll want to replace pleated air filters and oven filters in your home every 90 days. Warm air in winter and cool air in summer end up moving along the same “routes” and the same filter. As air moves through a building's air conditioning system, air filters trap and accumulate large and small particles such as dust, allergens and microorganisms. If you're a pet owner, you'll want to change your air filter every 2 months, especially when winter turns to spring and summer to fall.