Energy Tips
If you are trying to save on your heating and cooling costs and you are making improvements by air-sealing and adding insulation, ventilation becomes increasingly important, not only from a control standpoint, but also for health and safety reasons. From my discussions with homeowners, I often hear that they don't understand the need for ventilation. If their houses are already too drafty or too leaky, why would they need to consider ventilation? It is true that most homes in New England are too leaky and have an air exchange rate with outside air that is much higher than the standard set by The American Society of Heating, Refrigerating and Air-Conditioning Engineers. It has established a standard of 35 percent air changes per hour rate (or about 100 percent every three hours) for healthy homes. However, the problem is not simple leakiness but that most homes leak randomly, and the homeowners have little control over ventilation. A good ventilation system will help improve air quality, manage moisture and dilute potential pollutants.
Crazy as it sounds, once you embark on sealing and insulating, it makes sense to evaluate and install proper ventilation at the beginning — before you start. This is particularly true if you, for example, foam seal your rim joist in the basement and basement walls. You may be causing a significant change in air flow into the basement and creating a potential back draft condition in which flue gases are entering the basement and flowing up into the house through the walls where wire and pipe penetrations exist. When sealing or insulating, a combustion safety test of the furnace or boiler is always needed to ensure safety.
Installing adequate (or background) house ventilation can be as simple as upgrading a bathroom fan. The new fan should be moderately powerful, rated for continuous operation and quiet. For most New England homes, a fan that is rated 70 to 120 cubic feet per minute is adequate. As an exhaust fan only, the fan pulls fresh air through all the cracks and gaps in the house — even in the more air-tight homes. The fan should always be vented directly to the outside with the shortest and straightest duct run possible.
A key component of a background ventilation fan is its controller. In general, the fan must be capable of running on a pre-set timed schedule and have the capability to run continuously if necessary.
A better, but considerably more expensive approach to house ventilation is a whole-house ventilation system. Heat Recovery Ventilators and Energy Recovery Ventilators mix outside air with inside air as it is introduced to the house. This saves on energy as well as heating and cooling costs. However, these can also be very challenging to retrofit to an existing home.
Incidentally, whole-house fans that I often see are great at exhausting air to cool a house during the summer, but they typically are not closed and sealed properly in the winter months and contribute to significant heat loss.
In summary, the best approach is to seal up your house as tightly as possible and install proper ventilation. This will put you on a path to saving on heating and cooling costs as well as gaining better control of your comfort level in your home while maintaining a safe air-quality environment.
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Tim Gould is director of Energy Egghead, an Amesbury-based company that can be found at www.energyegghead.com, and provides professional energy audit and conservation services.
