Humidifiers and heating systems, a misunderstood and often misused combination
The purpose of the Barometer humidifier is said to be that a forced air heating system “dries out the air” and therefore additional indoor moisture is needed.
So is this empirically true?
The answer is simply no.
The indoor environment is relatively moist. Breathing, cooking, bathing all create moisture. Add to that moisture from unwanted sources such as a leaky basement or dirt crawl space without a vapor barrier and we can have a fairly moist indoor environment. In some instances too moist. So why would one want additional moisture in an already “damp” house?
Stack effect In spite of the moisture generated by the occupants and other sources, the air inside the house can become dry. This can occur through several different ways. One cause is the indoor moisture is diffused out of the house, driven out by the stack effect. But what goes out must be replaced. This brings us to another scientific idiom; nature abhors a vacuum.
With the stack effect, the basement of the house will be at negative pressure. A proverbial vacuum. And we know that vacuums suck. We also know a house is anything but air tight. That is unless it’s newer and built with special attention to sealing all the little voids that are everywhere in a wood framed house.
I deliberately left one major appliance out of the list, the heating system. Depending on the type of system, the furnace or boiler is the single largest contributor to drying of the air inside your house. Not by the myth of conventional wisdom that the act of heating dries the air, but by assisting the stack effect. To add insult, the air that is pulled into your house is cold and has to be heated. Fortunately not all heating systems cause suction and drying. Closed systems such as high efficiency gas fired boilers or furnaces do not contribute to the cooling or drying.
One more important scientific principle regarding air and moisture, relative humidity. Relative humidity (RH) is the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature. This means that air at 25º F with 40% RH will have an RH of 8% at 70º F. Both air samples are dry although the colder sample appears not to be nearly as much.
So does the heating system really dry out the air inside the house? As I have explained, no, not by the act of warming the air. In fact the furnace can help maintain indoor RH if the unit is closed loop combustion.
If there is a need for humidity, an in room portable humidifier unit is in my opinion a better option. With room humidifiers the user can better monitor the device, particularly the filter and clean it as necessary. And one more scientific fact that I’m fairly certain leads to over use of humidifiers. Human beings can not sense large variations in humidity. Make certain to have a hygrometer to monitor the indoor RH.