Airing Out Ventilation Questions

How much outside fresh air is needed to maintain a healthy indoor environment? 

The answer--to every one of these questions--is, "It depends." Generally, the more fresh air occupants get, the better. But not always; excessive drafts may lead to thermal discomfort and can even cause health problems of their own. Some people need more fresh air than others, so are we aiming to satisfy the most sensitive minority? In extreme cases, there will be times when the indoor air is healthier than the outdoor air. Since there is no absolute answer to this fundamental question, it's no surprise that simple answers don't exist for the other questions.

Is continuous ventilation necessary? 

"Continuous ventilation" typically means providing fresh air 24 hours per day, 365 days per year, which is a good thing. Some designs make it difficult for the occupants to switch the system off, however. Continuous ventilation raises construction costs, consumes a significant amount of energy, and requires regular maintenance to ensure effective operation. It is important to realize that a continuously operating ventilation system does not ensure a continuous flow of fresh air. For example, there will be times when the ventilation system is temporarily overwhelmed by either external or internal forces (such as kitchen ventilation fans). In addition, perhaps 5% of occupants will disable or defeat the systems: This form of consumer backlash cannot be ignored; a system that provides adequate ventilation to 100% of the occupants may be better than one that provides excellent ventilation to 95%. 

Is our present technology up to the challenge of providing ventilation? 

There's a whole new generation of sensors, microprocessors, and ventilation systems appearing that can make ventilation more reliable, more economical, and nearly invisible. But will they still work in 20 years? Frankly, the general level of training of American contractors is so low that only an optimist expects them to install sophisticated, reliable ventilation systems all the time. Incorrectly installed systems can actually exacerbate ventilation problems.

What about windows? 

Lots of people open windows to provide natural ventilation, even during the coldest winter or hottest summer days. This ventilation is often inadequate, but should its contribution be ignored? After all, opening a window is free and uses no energy but the push of an arm. This question is just one of many involving personal responsibility. Another is, "Should we allow people to adjust their ventilation systems to meet their own requirements?"

What strategy should we use when gas-fired appliances or fireplaces are present? 

This one looks solvable. We should be moving as rapidly as possible toward sealed-combustion appliances, or simply moving all combustion outside the conditioned space so they will not be affected by the ventilation strategy. Unfortunately, there's little progress on this front.

These and other questions about ventilation are discussed in "Forum Brings Fresh Air to Ventilation Issues," on page 15, where four ventilation experts offer some intriguing answers. What's clear from the ongoing discussion is that the question of mechanical ventilation in homes can't be ducked. It will require major research, new technologies, revisions to building codes, training for contractors, and education for consumers. 

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