It’s daylight savings time! Did you change the batteries in your smoke detectors? Many of us use the time change as a reminder to do this. But have you considered some other health and safety considerations in your home that spring’s arrival should remind you of? Let’s talk indoor air quality. Do you regularly change the air filter in your HVAC equipment’s air handler? A lot of us use the types of filters that should be changed every 30 days. If you’re not that methodical, how about at least making sure that you change them when the time leaps forward or back.
The air handling unit (AHU) is the fan that forces air throughout your homes system of duct work. It pushes the air through your furnace, heat pump or evaporator coil to deliver hot air throughout the house during the winter and cool, dehumidified air throughout the house during the summer. When outdoor conditions are more temperate in the spring and fall, you may also have your AHU set to run simply for the purpose of circulating air around the house so that rooms don’t feel “stale.”
The traditional purpose of your air filter is to protect the fan and other components inside your HVAC equipment. The filter removes dust and other debris that can build up on fan blades, inside duct work and elsewhere, which decreases the efficiency of the air movement and reduces the life span of the equipment and duct system. But increasingly, air filtration systems are becoming equally, if not more, important in protecting occupants’ health as they are in protecting the HVAC equipment. This change is a by-product both of the shift towards greener, more energy efficient homebuilding trends as well as the increase in recent years in respiratory ailments owing to larger, less easily definable causes.
A more tightly constructed home reduces air leakage between the inside and outside of the house, making it more energy efficient. This is good, of course, but both common sense and responsible building science tells us that if the indoor environment is more isolated from the outdoor environment, we need to pay closer attention to the quality of the isolated air that is being continually recirculated for the homeowner to breathe. This calls for a four-tier strategy: reduce contaminants, exhaust and control humidity, ventilate properly, and proper filtration.
1. Reduce contaminants
Reduce the introduction of contaminants into the home in the first place and remove those that are already present. Think about what you are bringing into your home on your clothes and in your shopping bags. Dirt, chemicals and many other unpleasant substances will hitchhike into your house on your shoes, so leave them at the door and by all means don’t drag them across carpets, rugs and other fleecy surfaces that will capture and re-emit the contaminants into the air. Also, think about all those cleaning products, air “fresheners,” paints and solvents, and even new carpets and furniture that you bring into your home, and be thoughtful about choosing low VOC and other environmentally conscious alternatives, and about where you use them in your home.
If your home was not built to high standards for air tightness, it is likely exchanging a large amount of indoor and outdoor air throughout the year. While reducing energy efficiency, this exchange also brings dust, humidity and even more obnoxious stuff into your home through some of the most unpleasant parts of your house: the crawl space and attic. Having your crawl space and attic air sealed, where spray foam and caulk are used to plug up holes made for plumbing, electrical, mechanical and other penetrations, is a significant step in improving both the energy efficiency and indoor air quality of your home.
2. Exhaust and control humidity
Some of the threats to indoor air quality are generated from within. In particular, bathrooms and kitchens are locations where high humidity and concentrations of grease, chemicals and odors are relatively high. Other places in the home that can benefit from “spot ventilation” – i.e. exhaust – include workshops, craft studios, and garages.
How old are the exhaust fans in these rooms in your home, and how well are they functioning? Furthermore, where are they exhausting those high concentrations of moisture and volatile organic compounds? A typical bathroom exhaust fan should pull at least 50 cubic feet per minute (CFM) out of the bathroom, and a typical kitchen exhaust fan should pull at least 100 CFM. A quick test for your bath fan is to place one square of toilet paper up against the grill while the fan is running. If the paper is held in place by the suction of the fan, then it’s probably doing its job. But if the paper falls, you should consider having it inspected and possibly replaced.
You probably know how well your kitchen exhaust is working by how well it clears out the kitchen whenever you cook something particularly fragrant. Is your range hood fan merely a “recirculating” fan with a filter, or does it truly pull the air out of the kitchen and exhaust it to the outdoors?
Speaking of exhausting to the outdoors, you should have the exhaust ducts for any fans checked to see whether they connect all the way to the exterior of the building. Many exhaust ducts lead only into the attic space, where they dump all the humidity and other poor components of the air there. This poor air quality can at the least migrate back into the home, and at worst create condensation on your roof structure, leading to moisture damage and potential structural problems.
While spot ventilation helps to deal with localized concentrations of humidity, the location and performance of your home in combination with seasonal changes and the needs and sensitivities of the occupants may suggest the installation of a whole house humidifier or dehumidifier. An ideal relative humidity level is between 40% and 60%. At this range, humans tend to be the most comfortable, and many unwelcome inhabitants like mold, mildew, dust mites, bacteria, to name a few, tend to be least comfortable. In order to control the relative humidity of your home, consider adding humidification and/or dehumidification capacity to your HVAC system.
While a garage is technically not part of your home’s interior, it is usually connected to it via the garage entry door into the house. This interface presents a risky exchange between the indoor breathing environment of your home and one of the most noxious breathing areas: along with cars, gasoline, paints, pesticides and many other foul air producing components, the risk of a car left running can lead to deadly instances of carbon monoxide poisoning. The safest way to protect your family is to install a CO monitor inside the house near the garage door, and to install a garage exhaust fan.
3. Ventilate properly
Some contaminants will inevitably make their way into your home, so these should be diluted by a responsible fresh air ventilation strategy. This is particularly important in tightly built homes. Older homes tend to have lots of “passive” ventilation – i.e. the house is leaky enough for plenty of fresh air to get into the house from the outside on a regular basis. However, as previously mentioned this sort of ventilation is uncontrolled and the air is likely to be channeled largely through unpleasant places like crawl spaces and attics.
In a well-sealed home, the occupant has a better opportunity to define how and from where the home gets its fresh air. One way is to add a duct directly from the outdoors into the return side of your AHU. Whenever the fan runs, it will pull in a certain amount of fresh outdoor which gets distributed throughout the house via the duct system.
An even better solution is the installation of an Energy Recovery Ventilator (ERV). This stand-alone piece of equipment pulls fresh air into the home via a dedicated duct from the outside, and at the same time exhausts indoor air at roughly the same rate, thereby providing a balanced exchange of fresh air and stale air. Additionally, the two air streams pass close to one another through a heat exchanger, where heat energy is passed from one stream to the other. In the summer, for example, some of the heat in the outdoor air is passed off to the stream of cooler, exhausted air from indoors, so that it reduces the load on the air conditioner to deal with this introduced heat. The reverse process happens in the winter. An ERV likewise exchanges some of the humidity in a similar way.
4. Proper filtration
So let’s say you’ve provided proper contaminant control, made sure all your exhaust fans are working well, addressed humidity control, and established a responsible way to ventilate your home with fresh air. Your last line of defense is your filtration strategy. Filtration is a highly occupant-specific aspect of providing good indoor air quality, because everyone has different sensitivities.
Airborne particles are rampant in nature and in our homes. Dust, pollen, pet dander, chemicals, bacteria, viruses, and microscopic creatures of endless varieties – all can be present in even a well built and ventilated house. And any individual person can have widely varying reactions to any of these components of air. Asthma, allergies, chemical sensitivities and a host of other conditions can make breathing or having other contact with these particles anywhere from unpleasant to deadly.
Green Horizon can help analyze and improve your indoor air quality. Our team of experts perform home assessments and blower door tests and we use the results to recommend the best solution for your particular home. Our team sees your home as a complete system, and because we aren’t tied to any one technology, we will always recommend the best solution for you.