Year: 2018

Indoor Air – Comfortable or Healthy?


The science correlating clean air with health issues is still evolving. There is no standard definition of “Clean Air”. As a result, most standards for building indoor air quality (IAQ) are established based on people’s perception of air quality. In this article we will examine both perceived air quality and actual clean air. We will present our conclusion and recommendations for achieving the healthiest indoor air possible.

Comfortable Air

Perceived Air Quality (PAQ), as the name indicates, is the subjective assessment of air quality by those living in a home or working in a business environment. Home builders want to build homes that meet the wishes of the occupants. To determine what standards must be achieved to that end the builders conduct field studies in which sample subjects are exposed to different environment conditions, and their satisfaction with that environment is recorded.

A typical study [1] varied three levels of air temperature and humidity and two levels of ventilation rate. The values for temperature and relative humidity were:

20 Degrees C/ 40% RH, 23 Degrees C/ 50% RH,26 Degrees C/ 60%RH

Ventilation in these tests was set as:

10 liters/ second per person

3.5 liters/ second per person

Other studies [2] have examined the effect of CO2 on air perception quality.


These studies show that there is not a single value for the parameters studied that would assure an acceptable perceived air quality. The studies only show that air is perceived as acceptable when it is cool and dry and unacceptable when it is warm and humid. The ideal conditions depend on your geographical location and time of the year. Ideal Humidity is between 30% RH and 50% RH. For example Canadian standards recommend 35% RH in winter and 50% RH in summer

Other recommended values are CO2 less than 1000 ppm and ventilation rate above 0.5 air change rate per hour( or 14 liters/sec per person).

Other factors are also considered for improving comfort. For example a Danish labeling system for building primary emissions of volatile organic compounds (VOC) [3] focuses on comfort by minimizing annoying odors and mucous membrane irritation. The values of the VOCs should be below levels that can be sensed by the occupants. These levels have nothing to do with health impact. As we can see the emphasis is on maximizing the air quality perception, not the health of the building occupant.

Healthy Air

The science of clean air is still evolving. There is no standard definition of “clean air”. Scientific studies have focused on specific issues related to the ambient air such as the effects of radon, formaldehyde, sick building syndrome, air particulates, VOCs and ventilation. But all these studies were focused on the specific problems noted above. There is no single science branch that addresses all the above factors together as one subject. However, there is mounting evidence of the importance of indoor air pollution and lack of adequate ventilation in establishing a healthy air environment.Getting an Air Quality Monitor for your home is a good first step to improve your indoor air quality. Continue reading “Indoor Air – Comfortable or Healthy?”


Winter Months Challenge

Winter is almost here and new challenges to clean indoor air are upon us now. In spring and summer we worry about outdoor allergens like pollen and also about pollution created indoors from cooking, and smoking, and VOC’s. Air conditioning keeps us comfortably cool in the noon and afternoon hours. Opening windows in the morning or late evening to let fresh air in insures that we have fresh outdoor air and meets the recommended ventilation rates. Air purifiers add another level of insurance.

But in the winter months’ ventilation is more difficult. We tend to seal the home tighter, add insulation to windows and doors to prevent heat losses and reduce heating costs. But these actions create new problems.

Lack of adequate ventilation allows pollutants to accumulate inside the house and operating furnaces add to the level of CO2 and even increase the risk of carbon monoxide poisoning.

We have to be more vigilant. Also, the holiday season with the added fragrances, to make the home smell “nice”, add to the problem with the increased emission of VOC’s.Click here to see my recommendation on a very efficient HVAC filter.

Importance of Ventilation

Ventilation is still necessary, we must expel the stale air and allow the intake of fresh air. Ideally we should have installed a heat recovery ventilator (HRV) that extracts heat from the stale air that is exhausted from the house and transfers it to the incoming fresh, but cold, air. It is a heat exchanger where the exhaust air warms up the incoming supply air. These systems may be expensive to install but will provide energy savings since the furnace will cycle on less frequently. However, even if you do not have an HRV in your home you still must have ventilation.

But I want to stress that you must have CO, carbon monoxide, detectors in your home since malfunctioning furnaces can be lethal. Continue reading “IMPROVING INDOOR AIR QUALITY – WINTER MONTHS CHALLENGE”




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”




Politicians are proposing or implementing Cap and Trade policies with the intended goal of reducing Greenhouse Gas (GHG) emissions. This a worthwhile goal that we should all support. However, when legislators and attorneys write the rules of Cap and Trade the process becomes unnecessarily complicated. The basic premise of Cap and Trade is that Companies that exceed GHG emission standards should pay a penalty or purchase an allowance for polluting from Companies that do not pollute. It is claimed that this process will encourage the polluters to not pollute in order to cut costs. In this paper we propose that money from penalties assessed under Cap and Trade policies be used to help CO2 sequestration through reforestation in locations recommended by the scientists.









To study the effects of GHG emissions we need to look first at the magnitude of the problem and then review possible solutions. A brief summary of the facts follows. Continue reading “CAP AND TRADE POLICIES”





Adequate ventilation is a key factor in achieving indoor air quality (IAQ).Our goal is to remove particulates and VOCs from our indoor environment. We can achieve this goal through ventilation, through portable air cleaners or a combination of both. The proper balance between the two will depend on our specific situation.

A brand new home will have been designed to meet local building standards, which in most places specify ventilation requirements. Since new buildings are designed mostly for energy savings they are typically built to minimize energy losses and are therefore tightly insulated, minimizing air infiltration. But new buildings make use of synthetic materials that introduce new contaminants such as volatile organic compounds (VOC) s.

So, if you have a brand new home you cannot assume that you have good indoor air quality. On the other hand, if you live in an older home you probably have a large outside air infiltration. Depending on your location, this air infiltration may carry pollutants which you must remove along with the pollutants created indoors from normal living. Furthermore, your older air ventilation system, if any, may not be adequate.

In this article we will examine common sense approaches for improving indoor air quality. Continue reading “VENTILATION- HOW MUCH IS NECESSARY?”

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.




What the Scientists tell us

There is considerable research in academia on ambient air quality. However, ambient refers to outdoor air. Most of the research consists of statistical analysis of hospital admissions for respiratory problems or mortality rates on days when there is extreme air pollution.

The statistical analysis consists of what scientists call meta-analyses (systematic reviews) of single-city time series studies. Basically an average of multiple studies.

The only indoor air studies are those that investigate the effects of indoor open fire cooking.These are important studies, mostly by the World Health Organization (WHO), but they only apply to underdeveloped countries where these practices are unfortunately still prevalent. They are not relevant to indoor conditions in the modern world.

Scientists are still divided on what standards should be imposed on ambient air. The U.S. Environmental Protection Agency (EPA) promulgated the National Ambient Air Quality Standards (NAAQS) designed to establish regulation of fine particulate pollution. But other scientists believe that these standards are too lax, with allowable pollution levels above the standards of the World Health Organization (WHO).

The science of clean air is not settled.

The statistical studies of ambient air have, however, one important conclusion. They tell us that the pollution effect on human health depends in part on the size of the particles in the air.

In this case size matters.

We can use this information when we address indoor pollution solutions.

But improving indoor air quality in our homes is our individual responsibility.

We cannot wait for solutions from the academic world. Continue reading “INDOOR AIR POLLUTION -WHAT ARE THE HEALTH RISKS”

Green Buildings and Indoor Air Quality – Energy Efficiency or Clean Air?

Building Construction Industry

The construction industry has made great strides in improving building construction.

New building codes and credits for Green Buildings have resulted in more energy efficient buildings and the use of recyclable materials for greater sustainability.

However these advances have not necessarily improved the indoor air quality (IAQ). Modern homes and offices are frequently more airtight than older structures resulting in reduced exchanges between outdoor fresh air and indoor air.

Furthermore, modern buildings make greater use of synthetic building materials that have introduced new contaminants such as volatile organic compounds (VOC), which arise from sources such as paints, varnishes, solvents and preservatives.

The combination of reduced ventilation and the increase in volatile compounds has the potential for a buildup of toxic substances in the home environment.

In the USA as in many other countries, no federal law specifically regulates IAQ, even though people typically spend more than 90% of their time indoors.

Pollutant levels are typically several times to several hundred times higher indoors than outdoors, and consequently indoor air typically accounts for over 90% of human exposure to pollutants.

Building Certification Programs

Green Building Certification programs have increased globally with over 145,000 green certification projects concluded as of 2016 and are forecast to grow by 37% by the end of 2018.The European Union Directive of Energy Performance of Buildings foresees that by the end of 2020 all new buildings should comply with the goal of nearly zero energy performance.[1]

The major Green Building Certification Programs include the Building Research Establishment Environmental Assessment Methodology (BREAM) in the United Kingdom and the Leadership in Energy and Environmental Design (LEED) in the USA. These programs are used in multiple countries around the world. Other significant programs are the Comprehensive Assessment System for Built Environment Efficiency (CASBEE) in Japan and recently (2016) the Deutsche Gesellschaft für nachhaltiges Bauen (DGNB) system in Germany. However there is no standard criteria that is used universally to define a Green Building. Different systems emphasize different Building characteristics.

But these projects, which give credits to builders for compliance, emphasize efficient use of resources (e.g., energy, water and materials) and sustainability.

But not much incentive is given for improving  Indoor Air Quality (IAQ).A recent study found that credits for IAQ accounted for only about 3 to 11% of the total credits.

This relative small percentage of credits for IAQ may be seen as inadequate incentive to pursue these credits.

Green Buildings and Health

Updates to the early Green Building Certification Systems now provide more weight to IAQ. Furthermore, other programs such as the WELL Building Standards [2] are focused specifically on IAQ. Typically Green Building Certifications have different requirements or Categories that need to be met in order to get the Certification. Some of the requirements address Pollution Source Control, Ventilation, and limits for specific pollutants such as formaldehyde, CO2, Volatile Organic Compounds (VOC) s. In addition they may require IAQ measurements. But the majority of requirements emphasize energy savings, water usage, building air tightness, minimize environmental disruption, and sustainability.

Many certificate programs allow “trading” of credits between categories. It may be possible to obtain Green Building Certification without complying with any IAQ requirements. One program, the German DGNB, is the exception in that it does not allow credit trading. Some compliance in each category must be achieved to get their Certification.

One problem that undermines improvements in the levels of IAQ in Green Buildings is that there is no consensus on what good IAQ is, or what factors affect the health of the occupants. Another problem is that some of the “green practices” used in the construction of Green Buildings have negative effects on the IAQ. In example using recycled materials may introduce in the building pollutants or toxic chemicals originated in the recycling process. Another example is the required use of green cleaning products for building maintenance. Many of the so called green cleaning products do not list all of their ingredients and may include fragrances. Fragrances are chemical additives that are dangerous pollutants that, when combined with ozone, can create secondary pollutants that have been proven to affect the health because of their microscopic particles that easily penetrate the respiratory system. In fact the US Centers for Disease Control and Prevention, Indoor Environmental Quality Policy states: “Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC”  [3]. Green Buildings have the potential to be beneficial to Health. However, we are not there yet. Progress is slow. It is up to us to control the pollution generated in our homes and to insure that we have adequate ventilation.[4]


It is my conclusion that we cannot rely on government programs to improve IAQ.

Improving indoor air quality of our homes is our individual responsibility.

Adding an Air Purifier can be part of our plan of action.

Click here to find out how you can check the air quality in your home.


[1] Anne Steinemann et al. Ten Questions concerning Green Buildings and indoor air quality.Building and Environment 112 (2017) 351-358

[2] WELL,The International Well Building Institute.The WELL Building Standard,V 1.0,Delos Living LLC,New York,, NY.,2015

[3] CDC,US Centers for Disease Control and Prevention. Indoor Environmental Quality Policy,2009,pp.9-10





About me

Hello, I am Carlos Gusts, a retired Industrial Engineer.

Now that I am retired I have the time to research and study the subject that is my passion.

How to achieve healthy indoor environments

I have seen first hand how indoor pollution affects people worldwide.Calling attention to what

improvements are  possible in this area can make a difference in people’s lives.I want to help.

Reporting on current research,and evaluating new products,is the mission of this website.

If I can be of any assistance please feel to contact me.

All the best,

Carlos Gusts

P.S. As a retired person I am also involved in research related to what makes retired persons thrive,not just survive. If you are interested you can visit my website on the subject