An article recently published in the Proceedings of the National Academy of Sciences, "Absolute humidity modulates influenza survival, transmission, and seasonality",  by Jeffrey Shaman and Melvin Kohn, confirms what we suspected all along. Dry air is not good for you! Not only does excessively dry air in buildings lead to discomfort, chapped skin, and respiratory problems. Now this study has shown that influenza infections are more likely to occur when the absolute humidity in the air is low.

The question that Dr. Heet wants to answer is, how can you increase the humidity and improve the level of comfort in your home?

1. Install forced hot water (baseboard radiators) instead of forced hot air systems. A circulating air mass transports humidity out of the living area into the furnace, where it gets removed from the air.
2. If you have to live with forced hot air, install inline humidifiers or room humidifiers to add humidity. Any kind of humidifier requires a lot of maintenance. The best room humidifiers that require the least amount of maintenance are German- or Swiss-made ultrasonic models. Unfortunately, they are also the most expensive.
3. Lower the room temperature (forced hot air systems will condition the air even in the winter and extract moisture from the air, thus lowering the absolute humidity in the air).
4. Briefly open the windows before you go to bed
5. Use body lotion after every shower

Unfortunately, none of the above can make up for the disadvantage of a forced hot air heating system. Even powerful room humidifiers can raise the humidity only so much in between the furnace cycles. As soon as the thermostat calls for heat, whoosh, there goes your humidity. Creating humidity only to have it extracted from the home again is a very inefficient use of energy, and it makes very little difference to the level of comfort (but it still does make a difference). A baseboard system, on the other hand, only lowers the relative humidity in the room (by raising the temperature), but the absolute level of humidity remains constant. Thus, operating a humidifier in a room that has baseboard heat makes a big difference.

Dr. Heet cannot emphasize enough what a bad idea the invention of forced hot air heating systems was. It is about time that we return to common sense in residential HVAC installations.