I hope the title got your attention and raised doubts in your mind, especially about making homeowners wealthier. I know what you’re thinking: "Ventilation is the act of bringing outdoor air into my home, so what happens when it’s hot and muggy in the summer, or freezing cold in the winter? Letting that outside air inside means that my air conditioning or heating bill goes up, not down. Right? End of story?"
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Not quite. In truth, that story has just begun. The key here is to understand how one can ventilate intelligently to both improve your health and save on energy, and reduce repair bills, and health care costs. First let’s deal with the issues conceptually so you fully understand what kinds of ventilation are most effective and beneficial to health and the least costly, and then we can look at scientific studies that have documented the health benefits and cost savings.
Conceptual Explanation of Ventilation and Exhaust Principles
Let’s do a conceptual experiment. Consider living in an airtight chamber in which we continuously emit some odorous and toxic gasses and particles, and maybe some viruses and bacteria. (Actually, super energy-efficient buildings without adequate ventilation can become like this chamber). It is easy to imagine what would happen. The concentration of all those contaminants inside your home would continually rise and the home would quickly become unlivable.
Let’s now try to make this chamber a healthful, livable environment. Imagine that we made a single hole on one side of that chamber and tried to blow in clean air to ventilate it, or, tried to suck dirty air out with an exhaust fan. Unfortunately, since the chamber is airtight, you couldn’t do that because there is no place for the air to go. As you blow air into a building the rising air pressure just pushes back with equal force, and as you suck air out, the depressurization tries to pull air back in. It would be like closing your mouth over a soft drink bottle and trying to blow air into it or suck air out of it. You would need to have one or more added holes in it to do either of those things. You need to have more than one hole so when air is blown in, an equivalent amount of air escapes through one or more other holes, and vice versa, if you forcibly exhaust air out. Thus, a key concept for ventilation and exhaust is that pressure forces should always be in balance - i.e., the sum of all ventilation inflows is equal to the sum of all ventilation exhaust outflows. That’s an important principle to understand.
So let's put another hole on the opposite side of your chamber-type home, then introduce a continuous flow of clean air into one of the holes. Now you have a steady flow of clean air entering and an equal flow of contaminated air exiting. What would happen to the concentration of those contaminants inside? As long as the rate of exhausted contaminants is greater than the rate that the contaminants are being emitted into the home (emission rate), the indoor concentration of pollutants will fall. Indeed, a higher clean air ventilation rate will increase the exhaust air flow and thus remove more contaminants in a given period of time. Thus, the concentration of contaminants in the home goes down as the ventilation rate of clean air goes up, and the relationship is proportional. From this simple analogy, one can see that since the health of persons living inside a home improves with lower pollutant concentrations, their health is directly related to the clean air ventilation rate.
Smart and Not So Smart Ventilation Concepts
Now you’re thinking, "there’s got to be a catch." You are right. The above simple principle may not always work so well. For example, suppose we placed the exhaust hole right next to the clean air ventilation hole. This might have almost no effect on the pollution indoors because much of the ventilation air will take a short cut straight through the exhaust hole, and much of the air exhausted will be drawn back into the ventilation hole, leaving the air inside unaffected. This kind of problem is not unusual, especially in commercial buildings. In some homes also, it is not uncommon for the bathroom exhaust to be located close to the supply air vent indoors so some of the cleaner supply air gets exhausted rather than the contaminated air in the room. So here’s a second principle for ventilation. To avoid the short circuiting-problem, don’t put ventilation supply air vents too close to exhaust vents.
Alternatively, suppose most of the sources from which contaminants are emitted into the home are all in one location near a wall, and the exhaust hole is right above that while the ventilation hole is somewhere on the opposite wall. Now the contaminants will mostly travel from the source directly to the exhaust and hardly pollute the remaining living space. Wow! That kind of ventilation is very efficient in removing pollutants so I would need less ventilation to get the same pollution removal effects. Here’s another principle: For stationary sources of pollution, such as stoves or toilets, the exhaust should be close to the source, and the occupants should not be in the pollution pathway from the source to the exhaust.
Now let's go into a bathroom, with the window and door closed. Suppose the door is a tight fit, and you turn on the exhaust fan. What would happen? Actually, almost nothing because try as it might, the exhaust fan would not be able to remove much air. That is why a tightly fit door on a bathroom is not a good idea unless there is some other way in which air from the house or the outside can replace the air exhausted. Thus, if the door had a slight undercut or over cut to allow air in, the house air would replace the bathroom air and the outside air would have to replace the house air either through infiltration or through a purposeful ventilation opening. This is a demonstrated problem emanating from the first principle above which we now restate: Always make sure a home or room has sufficient replacement air to insure that exhaust fans can be effective in removing contaminated air.
Leaky vs. Tight Homes
Imagine that you have a really nice older home with a nice wood fireplace in the living room, a finished basement with a rec room, a separate storage room in which you have a washer and dryer, oil or gas furnace, and your hot water heater. The only problem you have is that this old home is drafty, especially in the winter. So you hire a local contractor to add insulation, seal up cracks, put in new energy efficient windows and add new siding. Wow, what a difference! No more drafts, and a much lower utility bill. You’re happy. But maybe the contractor didn’t understand basic principles of ventilation. Winter sets in and on the first really cold day you crank up the fireplace and get some nice logs burning - but whoa! The house fills with smoke. So you quickly open a window to let the smoke out and you notice that the fireplace smoke is now going up the chimney instead of coming in the house. So you close the window but now the fireplace starts smoking again. What a revolting development this is! It’s principle number one again. What happened is the chimney can’t draw smoke filled air up from the fireplace unless there is a way for replacement air to enter the house, just like our chamber example. You never had that problem before because your house leaked enough to allow that replacement air in. Now you have to open a window on a cold day to use your fireplace to heat your home and you think -“how unproductive is that!?” You decide to put the fire out.
Now you go to wash your clothes in the basement while your kids watch TV in the adjoining room. You finish a load and put it into the dryer and come back upstairs. Soon your kids yell to you about a strange smell that makes them feel sick. You go downstairs and realize that the flue gases from the furnace are not going out the flue but are coming back into the basement. What happened? Well, the dryer was drawing air out of the storage room and thus depressurized the room and drew replacement air into the room through the flue and brought the flue gasses with it. That is called “back-drafting” and is obviously dangerous because flue gases contain carbon monoxide and other nasty chemicals but are not as obvious as smoke from the fireplace, so it is a good thing that your children were sensitive enough to realize that something was wrong.
All this is a little scary, so you call a professional that understands ventilation principles and he arranges to feed the furnace with outdoor air through a pipe in the wall with a damper, and similarly the fireplace, and perhaps the dryer also if that is needed. Now you think how that was such a simple and smart thing to do. Outdoor air is allowed directly to the source that needs it without wasting heating or cooling energy. It helps the exhaust/flue system work to prevent combustion byproducts from polluting your home, even with your nice tight building envelop with energy efficient windows. Now you're thinking smart, and you wish your first contractor was more knowledgeable. The professional advises you to consider sealed power vented combustion equipment that is fed by 100% outdoor air when you are ready to replace your existing furnace and water heater. He seems to know what he’s talking about.
Next you notice that while the temperature in your home this winter is where you want it, your home seems to have excess humidity and there are signs of condensation you never experienced before. You’re thinking that this is winter and the air outside is dry, not humid, and you don’t know what’s happening? What’s happening is that everyday living, like washing dishes and clothes, showering, cooking and breathing releases a lot of moisture that used to escape but now has nowhere to go because your home doesn’t leak anymore. So you think, in addition to moisture and condensation that causes mold, what about all the chemicals coming off of the building materials and furniture and cleaning products that I read about, and the body odor, bacteria and viruses? These do not come from stationary sources but are distributed throughout the house. With a sealed house, how does all that bad stuff escape?
Is that really a problem? Yes. Let’s look at some history.
Historical Experience with Energy Conservation and Ventilation
After the 1973 oil embargo when energy prices rose dramatically, most people were looking for ways to conserve energy, including reducing the ventilation rates in buildings. During that time, it was not uncommon for schools and commercial buildings to cover up the intake vents designed to bring in outdoor air, and officially, outdoor ventilation requirements in standards were significantly reduced. The unintended consequence of these activities was a wave of adverse health and comfort symptoms that doctors had a difficult time diagnosing but that were clearly associated with occupancy of certain buildings, and these buildings became known as “sick buildings” and the illnesses became known as “sick building syndrome” or “building related illnesses”. While the world was becoming concerned about rising levels of outdoor pollution, scientific research later revealed that some kinds of pollution indoors were much higher than outdoors, and the main sources (but not all) of that pollution came from sources indoors. Thus, in addition to reducing the pollution emissions indoors, a new appreciation for providing adequate ventilation began to emerge, and there developed a kind of tug of war between the desire to reduce energy use and the need for people to be healthy and comfortable indoors. So now, we look for ways to provide the needed outdoor ventilation to buildings in the most energy efficient manner.
Ventilation Options
In older homes, the air leakage in buildings provides a significant amount of ventilation but because it is not directly controlled or conditioned, and it is not properly filtered, such ventilation can be very energy inefficient. In addition, outdoor air is not always so clean, especially in urban areas and while the house structure itself acts to filter out some of those contaminants (especially particles), they still enter in large amounts. By tightening up the building, you can reduce the uncontrolled inflow of dirty unconditioned air. Further, in addition to reducing the flow of dirty outside air, energy-efficient building envelopes filter out a higher percentage of outdoor pollutants. So that is a good thing. But it doesn’t solve the need to ventilate your home.
The solution is to make your home less leaky but to also mechanically provide controlled filtered ventilation air in the amount necessary to allow for needed exhaust of stationary sources, plus provide ventilation air to dilute all the other pollutants and moisture that gets emitted into the home. The idea is to stay healthy and still save energy.
Most homes have a forced air heating and cooling system, so the most common mechanical ventilation solution is to bring in some outdoor air and exhaust an equal amount of polluted indoor air through the forced air system, and use a filtration mechanism to filter out the particles. Since high efficiency filters generally tend to make it harder to blow air through, a medium efficiency filter is generally sufficient for indoor air quality purposes unless residents have special needs. To save energy, energy recovery ventilation (ERV) systems can be installed in many locations. These devices transfer the heat and moisture from the incoming outdoor air to the exhaust air in the summer, and vice versa in the winter, so that much less new energy is needed to condition the incoming outdoor air. In addition, traditional heating and cooling equipment has become much more efficient, and new technologies using desiccants to dehumidify and cool spaces are even more efficient. Thus, a highly energy efficient home with appropriate mechanical ventilation to satisfy exhaust fan requirements and dilution ventilation requirements, fitted with a direct air supply to properly vent combustion equipment can save energy and improve health. Energy and medical bills (including for over the counter medication) go down while health and human productivity improves.
The On and Off Problem – Don’t Override
In most residential systems, the blower fan only comes on when the system is heating or cooling, so that would normally be the only time that mechanical ventilation is provided. Unless you are one of those people that likes to open windows (most people hardly do so) your home will probably be under-ventilated much of the time. With a mechanically ventilated home, make sure you have an automatic control feature that will turn the blower fan on periodically so that your home gets ventilated, and be careful not to manually override the minimum or recommended settings for that control lest you compromise your health and that of your family. In addition, whenever the temperature and humidity conditions outdoors are more favorable than they are indoors, you can get "free" conditioning by increasing the outdoor air ventilation to save energy, rather than decreasing it. Devices that do this automatically in commercial buildings to save energy are called “economizers”, and since the health advantages of ventilation continue well beyond minimum requirements, that is a good thing to do.
Advances in Home Certification Programs
We have seen how retrofitting an existing home, or building a new home, to be energy-efficient can easily result in an unhealthy living environment. After having learned the hard way, the energy and indoor air quality communities began to join forces in the 1990’s to integrate energy and health needs of occupants. During that time, the U.S. Environmental Protection Agency (EPA) published a major modeling study for commercial buildings demonstrating that substantially raising mechanical ventilation rates did not need to result in dramatic energy cost increases. At the same time, the Department of Energy (DOE) was discovering better methods to measure home infiltration rates and to calculate ventilation needs for combustion, exhaust and general dilution ventilation requirements. Later DOE began introducing indoor air quality requirements into their Weatherization Assistance Program for low income occupants, and EPA introduced a program called Indoor airPLUS. This program adds special indoor air quality requirements on to homes that qualify for Energy Star certification for new homes. The program features indoor air quality protections involving moisture control, radon control, pest management, heating, cooling and ventilation, and combustion venting, and includes a homeowner’s education package. Thus, for new homes, one can find a builder that will commit to building a home that is certified as Energy Star and Indoor AirPLUS. The U.S. Green Building Council also introduced similar requirements for new home construction into its LEED for Homes certification program.
Evidence of Health Benefits from Healthy Energy Efficient Homes
So now we know how to have a home that both lowers energy bills and improves health. In general, there is ample evidence of the health benefits of individual IAQ features. Much of the research specifically linking IAQ provisions in energy efficient homes is drawn from analysis of the DOE’s Weatherization Assistance Program that is designed to assist low-income families. For these families the research documents a reduction of heating bills by roughly 30% and improvements in many aspects of health. Health benefits include reduced hospital visits of underweight children, reduced carbon monoxide exposure events, reduced number of school or work days lost to illness, plus improvements in general health, hypertension, sinusitis and asthma. Further, occupants reported significant improvements in general comfort. In addition, Canadian research shows that new occupants of energy-efficient homes with heat recovery ventilators (HRVs) report improvement in the symptoms of throat irritation, cough, fatigue, and irritability.
Making Sure Your Energy Retrofit Achieves a Healthy and Energy Efficient Home
The U.S. Environmental Protection Agency recently produced a voluntary guidance entitled “Healthy Indoor Environment Protocols for Home Energy Upgrades” that delineates best practices for protecting and improving Indoor air quality during home energy efficient upgrades . This guidance was produced in cooperation with the U.S. Department of Energy. Homeowners can make these protocols a contractual requirement and choose a reputable contractor with experience in energy efficient and healthy housing.
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