Category: Air Cleaners




In previous articles we have discussed the health risks of indoor pollution, the need for adequate ventilation and the desirability of having air quality monitors and air purifiers in our homes. However these benefits are only obtained if we have regular maintenance of our air cleaning equipment and air conditioning units. And most important is the use of correct air filters.


Types of Air Filters

There are mainly two types of air filters for particle collection.

– Fibrous Media Filters

There are two methods for evaluating this type of filter.                                                                                                             a) Test Method specified in The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Standard 52.2. This method evaluates the removal efficiency for particle sizes 0.3 to 10 µm in diameter. The results are reported as Minimum Efficiency Reporting Value (MERV).MERV numbers range from MERV 1 to MERV 16,based on average removing efficiency across 3 particle sizes in ranges 0.3 -1 µm, 1 – 3 µm, and 3- 10 µm. The higher the filter rating the higher the filter’s removal of particles efficiency. Filters with a MERV 13 and above ratings require at least 50 % removal efficiency for 0.3 – 1 µm particles (These are the size of particles that are the most harmful to human health). MERV 11 filters must achieve at least 20 % removal of these particles. The Environmental Protection Agency (EPA) recommends furnace filters with at least MERV 13 rating [1]. High Efficiency Particulate Air (HEPA) filters are generally equivalent to MERV 16 and offer the highest available particle removal efficiency of fibrous media air filters. Usually with a removal efficiency of 99 % or higher. Click here to see details on my recommendation for a very efficient HVAC air filter.

b) When the air filters are used in a portable air cleaning unit, the filter’s efficiency is measured by the unit’s Clean Air Delivery Rate (CADR). The CADR is a measure of a portable air cleaner’s delivery of relatively clean air, expressed in cubic feet per minute (cfm) Continue reading “AIR FILTERS”

Air Quality Monitors -Do You Need One ?



Indoor air quality monitors have improved significantly in the last few years. Advances in sensor and computing technologies have allowed the development of low cost air quality monitors that are portable and small in size and capable of being wirelessly connected to smart phones for real time monitoring and reporting the air quality in a room.

The explosion of new models has resulted in over-choice for the consumer. The recent models are designed to monitor some or all of the following air quality parameters.

  • Carbon monoxide (CO)
  • Carbon dioxide (CO2)
  • Volatile organic compounds (VOC)s
  • Particulate Matter (PM)
  • Air turnover
  • Humidity
  • Temperature

Different Air Quality Monitors are designed for specific ambient conditions. All of the above parameters affect our perception of what is a comfortable home. However, not all of these parameters are equally important for a healthy environment.


Most low cost monitors check the amount of CO2 .Scientists have established standards for safe levels of CO2 in an indoor environment. Since all humans exhale CO2 at the same predictable rate, the amount of measured CO2 in the building is used as an indirect measure of human bio-effluent concentration and building occupancy. Building code standards in the USA typically allow for a concentration of CO2 of 1000 ppm. So the amount of CO2 in the ambient air can be used as a way to control air quality. Some of the monitors can be connected to the home ventilation system so that when an unacceptable level of CO2 is reached the ventilation can start automatically.

This first step in monitoring ambient air is good, but it is not sufficient. Scientists have determined that small particulates, PM2.5 (smaller than 2.5 microns) are the most harmful to human health. These particulates can easily penetrate into our lungs and travel into our blood system. They can also transport toxic chemicals. Ensuring a healthy environment requires that we eliminate the PM2.5 particulates from the ambient air. So we should select an Indoor Air Quality Monitor that as a minimum allows us to monitor CO2, PM2.5 particulates and VOCs. (The VOCs are ultrafine particles, smaller than 0.1µm, and included therefore with the PM2.5)

The other parameters are of interest and important if we want to optimize comfort, but are not critical to our health.


Basic Models

These models give you a binary indication of air quality. Either Good or Bad. This indication could be in the form of a digital display or a color code, such as Blue for good, Orange for bad. It is a simple display of air quality but it is not a quantitative measure of the degree of pollution that is present. This type of Air Quality Monitor does not provide any details on the type of pollutant, nor what action should be taken by the user to correct the problem.

Models with Advanced Features

In addition to providing a binary status of the air quality conditions these models have additional features that allow you to find details. Visualization is most important .When combined with data logging, the users can see a chart or display showing the status of each parameter in near real time. The parameters displayed vary with different models.

It has been found that visualizing the problem allows the user to correlate the reading with an on-going activity, thus identifying what actions (cooking, cleaning, smoking, etc.) are causing the increase in indoor pollution.

Furthermore, awareness of the air quality associated with a specific activity promotes behavioral changes that will result in improved air quality in the future.

For those users interested in a better understanding of their pollution problem there are Indoor Air Quality Monitors that have wireless Wi-Fi connection that allows them to access web applications offered by the manufacturer. These apps allow the users to study the trend of measurements as they correlate to time of day, seasons, or other variables. These advanced models are intended for those users technical savvy, or professionals in the field of Building Science that study the interaction of Insulation, Air Conditioning, Ventilation and Air Quality.

Monitoring Systems

The models described above provide detailed information on indoor pollution. However, they do not help you to take action to correct an unhealthy air quality condition. The monitoring systems allow you to integrate the monitor with other home systems. This integration can be achieved through recipes or instructions available from (If This Then That).These instructions may allow you to connect a monitor to a smart thermostat, such as a Nest or an Ecobee thermostat, installed in an Air Conditioning unit or in an Air Purifier. If this connection is made, then the Air Quality Monitor can start automatically the Air Conditioning unit or the Air Purifier if the pollution level warrants it.Please note that not all monitors are designed to allow this integration.

A more advanced integration can be achieved using IoT (The Internet of Things) integration.This is a system being developed by many large companies,such as Microsoft and Amazon,which allows connectivity between all appliances or equipment used in home automation. I would suggest that this more advanced automation is best left to professional Home Systems specialists.


Improving Indoor Air Quality in our home is our individual responsibility.A suitable Air Quality Monitor can provide a good starting point.This is my recommendation on an Air Quality Monitor.

Choose wisely !




Indoor Air Quality depends on many factors. We are all concerned about removing contaminants from our indoor environment, but just as important is to have adequate ventilation.

If we live in an area with clean outdoor air, then opening windows and allowing natural ventilation is all that may be needed. Unfortunately few of us are so fortunate. In the modern world, in cities or suburbs, the outdoor air may not be so clean.


Furthermore, with the emphasis on saving energy, newer green buildings are frequently more airtight than older structures resulting in reduced exchanges between outdoor fresh air and indoor air. Airtight buildings result in increased concentration of indoor pollutants. Building Code standards for a healthy building in the USA require a ventilation rate of 15 cfm per person (equivalent to 7 liters/second per person). In the European Union the standard is .5 air turns/hour.

These standards are based on maintaining a safe level of CO2 in the indoor environment. Since all humans exhale CO2 at a predictable rate the amount of measured CO2 in the building is used as an indirect measure of human bio-effluent concentration and building occupancy. The standards of ventilation rates referenced above are equivalent approximately to a concentration of CO2 of 1000 ppm. This concentration is not considered harmful .Actually OSHA allows a concentration of 5000 ppm in industrial environments if a worker does not remain in that environment for more than 8 hours. However there has been research done in Europe that indicates that CO2 concentrations above 2000 ppm may have a detrimental effect on human performance of various mental tasks. In addition the higher concentrations have been considered a factor in the Sick Building Syndrome.

Forced ventilation can achieve these targets and the environment can be healthy provided that the Air Conditioning is equipped with HEPA in-duct filters that are properly and frequently maintained. Without these HEPA in-duct filters the achievable particulate air content will only be PM10 not the desired PM2.5.

We also have to consider the levels of outdoor CO2 in the air that is being introduced through ventilation. The air with the lowest CO2 level in the USA is in Hawaii at the top of the Mauna Loa volcano with a measured value of 366 ppm. But if you do not live on top of that volcano the average value in your area will be in the range of 375 to 450 ppm which is typical of urban areas.

To maintain the desired CO2 level indoors the ventilation rate must be adjusted accordingly.


Adequate ventilation is necessary, but not sufficient. Even if the amount of CO2 in our homes is maintained at a safe level we know that most indoor pollutants are created or formed indoors. Fine particles (smaller than 2.5µm and described by scientists as PM2.5 ) are the most harmful to human health .This category includes volatile organic compounds (VOC) such as benzene, toluene and formaldehyde from smoking, cooking, gas stoves, cleaning fluids, solvents, pesticides. We must reduce the presence of these pollutants in our homes.

Epidemiologic studies indicate that indoor pollution is correlated with morbidity caused by allergic diseases. A significant study was done in a test of 8 homes in Fresno, California. Air purifiers were installed in the living rooms and bedrooms of these homes. After the 12 week study the researchers concluded that air purifiers reduced indoor PM2.5 levels with significant improvements in nasal symptoms in children with allergic rhinitis, when compared to the control group of homes that did not have the air purifiers installed.

In another study,using data from the Exposures of Adult Urban Populations in Europe Study (EXPOLIS), researchers determined that when advanced filtration was used,a reduction in PM2.5 of  27% for residences of Helsinky,Finland, was achieved.


Although we may not know the specific health risks in our home environment,common sense dictates that we take action that is possible. Installing suitable air purifiers must be part of our plan of action.Improving indoor air quality in our homes is our individual responsibility.