November 12, 2007
Homes That Are Sealed Up Too Tight: More Energy Efficient But Less Healthy
By Michael D. Shaw
It was beloved Indiana poet James Whitcomb Riley (1849-1916), whose 1883 paean to autumn contained the memorable words:
O, it sets my hart a-clickin’ like the tickin’ of a clock, When the frost is on the punkin, and the fodder’s in the shock!
These days, though, people are a lot less worried about getting the fodder (feed for livestock) in the shock (a heap in the field), and seem to be obsessed with sealing up their homes tight as a drum, in an effort to save energy. Of course, with the price of oil approaching $100 per barrel, and all other forms of heating your house racing ever upward, what’s wrong with that?
In three words: Indoor air pollution
Simply put, your home is a dynamic system, in which various processes create chemicals and biological pathogens that can build up without proper ventilation. Too bad that this concept—not exactly rocket science—seems to be missing from nearly every TV sound bite on energy efficiency, flooding the airwaves at this time of year.
The fact is, prior to the 1973 oil embargo, that saw gasoline prices rise from about $0.30 per gallon to nearly a dollar, hardly anyone cared about energy, let alone conserving it. But, then came the somber warnings, the pointless all-year daylight saving time, and the wonderful predictions of how the vast reserves of North American tar sands and oil shale were going to save the day, once it became practical when oil hit $25.00 per barrel.
So, the public complied, as did the architects. and we were well on our way to much tighter occupancies. A few years later, though, so-called “sick” buildings began to appear, and folks faced a new set of problems at work and at home.
In a bellwether January, 1981 New York Times piece entitled “Dangers of Indoor Air Pollution,” health writer Jane Brody noted that…
“The air you breathe in your home or office may be hazardous to your health—more dangerous, in fact, than the outdoor air in the most polluted of cities. This is especially so during the cold months, when windows and doors are kept tightly shut and homes, schools and office buildings are made as airtight as possible to conserve energy.”
Brody went on to make a number of good points:
- Adverse health effects, such as headaches, frequent colds and sore throats, skin rashes, eye irritation, lethargy, dizziness, and memory lapses have all been linked to indoor air pollution.
- An old-fashioned “leaky” house might have effected a full air exchange with the outside every hour, but a tightly sealed residence could take four to ten times longer. As it is, ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) standard 62-1989 which specifies 0.35 air changes per hour, is probably not adequate for large sources of indoor pollutants or moisture.
- Nasty chemicals that can build up in typical homes include formaldehyde, nitrogen dioxide, carbon monoxide, and several hydrocarbons.
- Since moisture can accumulate in a tight house, the mycotoxins from mold are also a threat.
Tight houses can create conditions whereby exhaust devices—such as range hoods and clothes dryers—produce negative pressures that will back draft furnaces, water heaters, and fireplaces. Thus, carbon monoxide (CO) and other combustion products flow into—not out of—your house. While no figures are available on how many CO poisoning deaths are attributable to tight houses, homeowners should be mindful of this possibility.
So much for all the bad news. What should you do?
In most cases, the effects of a too-tight house will become apparent in fairly short order. The general unpleasantness associated with a stuffy environment will manifest itself. Newer tighter homes might exhibit moisture on windows, mold growth on cold surfaces, and dust mite infestations on carpets. There are also scientific tests to measure how tight your house is.
You can call in a good HVAC (heating, ventilation, air-conditioning) contractor, who will set up a blower door test. In this method, a powerful calibrated fan places your house at a positive pressure compared to the exterior. Thus, air is forced through all holes in the structure, exposing problem areas. At the same time, an evaluation can be made of the natural or passive ventilation rates, which in many cases will fall far below ASHRAE recommendations.
Best practice is to construct a reasonably tight structure with provisions for mechanical ventilation. Authorities recommend two to three air changes per hour, at a positive pressure of 50 pascals (0.2 inches of water). Fortunately, this usually requires little more than a continuously running 75 cubic feet/minute bathroom fan. More complex systems might tie this in with heat and humidity control.
Just don’t seal yourself up in a household tomb this winter!