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  NOTE: May Dooley passed away in March 2024. This site will remain available as a tribute to her.


Few modern houses have adequate ventilation. Drafty old houses may start out with sufficient ventilation but if windows have been replaced and insulation added, ventilation may be lacking there, too.

This section approaches the subject in a Q&A format, hopefully leading to a better sense of what ventilation is and why it is important.

Q: What is ventilation?
A: Bringing in fresh air and getting rid of stale air.

Q: Why are we talking about that? Most houses have central air.
A: Central air doesn’t bring in fresh air. It recycles stale air.

Q: Why do I need to be concerned about fresh air?
A: Every cell in the body needs oxygen. Fresh air also helps dilute gaseous toxins.

Q: So I should open a window?
A: On a still air day, there is not much air exchange. Besides, what if it is humid outside?

Q: How can I bring in fresh air that’s not humid?
A: What if the fresh air went through a dehumidifier as it came into the house?

Q: You mean, I put a dehumidifier by the open window?
A: Not quite, but suppose the fresh air came in through a duct, through a filter to remove pollen, and then into the dehumidifier?

Q: And from the dehumidifier the fresh air goes into the room?
A: Here’s a better idea: The dehumidified air passes through a second duct into the main duct of your central AC system.

Q: You mean, the fresh air would come out through the vents in all the rooms?

A: Yes, through all the supply vents!

Q: I like that idea. Why isn’t every house set up that way from the time of construction?
A: Maybe building code officers forgot that people need oxygen in homes, just as much as office workers do in large office buildings.

Q: How can I learn more?
A: Although this concept is making its way into some imported equipment, there is only one American manufacturer that has been around for a long time marketing this approach: ThermaStor, at www.thermastor.com. Look at their line of UltraAir dehumidifiers, or equivalent, which lends itself to the attachment of ducting. I have no financial connection with ThermaStor.

Q: So if one of these units was set up next to my air conditioning unit, I’d have filtered, dehumidified, fresh air coming into each room?

A: That’s right. Another plus is that since more air would be coming into the home than is leaving, there house would be under a positive pressure. That is, when you open a door, stale air would tend to be pushed out, helping to remove carbon dioxide and other gaseous toxins from room air.

Q: Is this the only approach for ventilation?
A: No, there are others. For example, there are HRVs (heat recovery ventilators) and ERVs (energy recovery ventilators). These are energy efficient, bringing in fresh air and exhausting stale air. In the winter, the heat from stale air is transferred to the cooler fresh air coming in. Some contractors and indoor air professionals have backed off from this technology because of reports of mold growing in ductwork, especially in flexduct, since dehumidification may not be adequate. If putting in an HRV/ERV, regular maintenance is essential.

Q: I’ll speak with my HVAC contractor about this.
A: By all means – but first understand the elements ThermaStor delivers for a healthy home. Make sure that whatever your contractor may suggest, that the approach should deliver fresh air, filtration, adequate dehumidification, and dissemination throughout the house.

That’s your checklist: fresh air, filtration, dehumidification, and dissemination. This concept is called "pressurized dehumidification" and it is viewed as an important component of healthy indoor air quality. The word “pressurized” refers to more air being brought in than is leaving the house, so the house is under a positive pressure.

Another plus to positive pressurization is that stale wall cavity air is less likely to penetrate into room air.

Q: What if my house has ductwork but it’s not in the budget to add mechanical ventilation as described above?
A: Put the AC fan in the “on” position. At least it will re-circulate oxygen and even out carbon dioxide from bedrooms at night.

Q: What if my house has no ductwork?
A: The dehumidifier might be set up in the basement, or in the attic, with a duct to bring in fresh air and one or more extending to living areas for the release of filtered, fresh, dehumidified air. Factor in vibration deadening material, because the dehumidifier has a motor.

Q: What if my house is dry during the winter?
A: The Thermastor product can be run with just the fan and the fresh air, without the dehumidification component.

Q: What if my house is old and somewhat drafty?
A: Maybe you have sufficient air exchange already. Modern houses are built so tightly that mechanical ventilation becomes more of an issue. You might get a basic carbon dioxide meter (Amazon) to monitor carbon dioxide levels, particularly in bedrooms at night. If carbon dioxide levels are going up, oxygen levels may be going down.

Let’s give the final word to Benjamin Franklin: “I am certain that no air is so unwholesome as air in a closed room that has been often breathed…and not changed.”

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This is the end of the Indoor Air Quality Topic.


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