Greening Your Ventilation

May 06, 2007
May/June 2007
A version of this article appears in the May/June 2007 issue of Home Energy Magazine.
Click here to read more articles about Moisture Problems

    Since today’s houses are now tightened for air conditioning as well as heating, there is less and less natural ventilation in our homes. This means that additional forms of mechanical ventilation are needed to deal with interior pollution.

    A healthy home is “dry, clean, well ventilated, pest-free, free from contaminants, safe, and well-maintained” according to the National Center for Healthy Housing. A green home should also be a healthy home, and ventilation is one of the principal ways we can ensure a green home’s health. If health were not a consideration in buildings, we could very well ignore ventilation. In this column, I’ll look at the role ventilation plays in making a home healthier from the start, and in maintaining its health after it is occupied. I’ll also explore the potential and limitations of ventilation in new and older homes.

    As technological advances have brought new tools to the ventilation field, building scientists are constantly struggling to come up with standards that will provide us with as complete and effective a ventilation strategy for each building as possible. The intense debates, which took place over several years, to develop ASHRAE 62.2 and Energy Star guidelines for ventilation equipment show how hard it is to close the loop on the perfect ventilation system.

    Thanks to these guidelines we can now do the following things effectively:

• We can install single- or multi port exhaust fans to remove primary point source moisture and pollutants from bathrooms, kitchens, laundry rooms, and attached garages by exhausting moist or polluted air directly to the exterior. However, we must be careful that the power of these fans does not backdraft space- heating and water-heating equipment, thus creating a potential health hazard. Eventually, all heating equipment will have sealed combustion and will be uncoupled from the interior air, but until then we must diligently avoid these risks.

• We can install intake fans that bring in fresh outdoor air and dilute many of the pollutants in indoor air. But we must not place the ducts for these fans so that they are importing as many pollutants through building envelope leakage as they are attempting to dilute. We want to be especially sure that we are not bringing in too much moist air. We need to install one or more effective filters to stop most particulates from entering. I remember investigating a home where there was a strong hamburger smell, pulled in through the venting system from a local McDonald’s restaurant. Not even good filters could stop this problem. We moved the intake vent to a downwind side of the house away from the McDonald’s, which provided some relief. It’s always good to place these vents so that they are away from dust, odors, and other contaminants.

• We can install balanced whole house ventilation systems to remove much of pollutants like radon, tobacco smoke, CO, NO, volatile organic compounds, mold spores, and other airborne allergens. Here as well we must be careful that we are not sucking more pollutants into the living spaces through the replacement air vent openings.

    In combination with controls like humidistats, timers, and gas sensor technology, we are getting closer to peopleproofing ventilation equipment and requirements… but we’re not quite there yet! While these guidelines are largely effective, they do not fully address all the moisture and pollutant sources in the home that are generated by the residents.

• Over the years I have been in many inner-city homes where a pot of beans or tomatoes is cooking nearly 24/7 and generating a great deal of moisture. It would require a fan operating 24/7 to address this moisture source, with the consequential energy penalties.

• I have been in homes where there are unvented combustion appliances used for heating, including natural gas and/or kerosene space heaters, and gas ranges and ovens that are operating 24/7. Persuading residents of the risks of such equipment is not easy when they cannot afford to pay the natural gas bills they get when they use their whole-house heating system.

• I have also visited many homes containing dozens and dozens of plants that are generating enough moisture to support mold growth on many different surfaces. Persuading someone who loves plants to give up some or most of them is a hard sell.

• In some of the homes I’ve visited, several adults smoke cigarettes all day long. The smell of smoke in furniture and bedding is very strong in these homes, and the side effects of the smoking leave vulnerable residents at risk.

 • Many homes have overstuffed furniture and carpeting that is treated with fi re retardants. These fire retardants are outgassing all the time, especially when the living space is warm and moist.

 • Bedding can be loaded with dust mites, and venting has little effect on reducing these infestations.

• Lead dust or pesticides tracked into the home are not likely to be removed by any amount of ventilation.

    In other words, there is no way we can create a ventilation system that will remove all pollutants. As long as residents do not understand that their behavior, and what they bring into the house, dramatically affects the health of the living space, pollution will stay in a home, no matter how powerful the ventilation system may be.

    We have almost reached the point where there is not much more we can do with ventilation technology in our homes. We need to educate builders, contractors, and homeowners in order to reduce the human error factor in ventilation practices. To this end, I recently helped Environmental Health Watch create some prompts for homeowners, to remind them of practices that will help keep their homes healthier—including being sure that they use their bath fan (see graphic/prompt).

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