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Q. I heard an ad on the radio for a whole house humidifier. Is this a good idea?
A. I’ve heard that ad too but you really need to know a lot more about what they do and the pluses and minuses before you make up your mind to buy one or not. The key is understanding what relative humidity is and how it affects you and your house. You hear or watch the weather reports and they always report a percentage number they call relative humidity. What that number refers to is the amount of moisture in the air at a given temperature. 100% and it’s foggy and raining. We seem to pay more attention to the humidity levels around here between June through September because when the outside temperatures get up above the mid seventies and the relative humidity rises to that level as well, the air becomes quite sticky and uncomfortable. It also is an indication of how well the air will accept more moisture into it. In agricultural areas the weather reports include a number known as a drying index so farmers can gauge the time crops will dry while being harvested. I hear folks complain that their respective heating systems drys out their air and they complain about discomfort, dry skin and even respiratory problems. That’s because we have a built in cooling mechanism in our bodies through perspiration. If the humidity is low and the temperature is up and we perspire, the evaporation of the perspiration from our skin naturally cools us. But it’s not the heating system that’s the true culprit. What’s happened is the air all around us outside might be 45ºF at 67% relative humidity but bring that air into the house and heat it up to 70ºF and the relative humidity drops to next to nothing. Warm air can hold more moisture than cool air can. Humidifiers are appliances that work to reintroduce moisture back into our air environment. Not only can warm air hold more moisture than cool air can but moist air feels warmer at 70ºF than very dry air of the same temperature. We can, through humidification, lower our heating loads slightly and thereby save some energy costs. Properly and comfortably humidified air not only makes us feel warmer but prevents wooden furniture from drying out and splitting. Museums and owners of fine art and historic and fine furniture absolutely need to have humidity controls. That’s the plus side of humidifiers. However, as a builder, remodeler and then home inspector, I have encountered humidifiers in all states of malfunction and disrepair and have been aware of medical studies that date back to the early 1970’s documenting ailments then called “humidifier fever” long before such things as Legionnaires Disease ever came into the language. I have torn apart ductwork downstream of an old humidifier to find all sorts of odd things growing in the ductwork perpetually hydrated by a malfunctioning humidifier. I have seen the undersides of roofs soaking wet during winter attributable to a humidifier pumping moisture into the household air-stream that ultimately migrated into the attic where it found the cool surface of the underside of the roof’s plywood to condense upon causing mildew and rot. Even the best of the humidifier designs tend to ultimately succumb to mineral deposits from the water supply and leakage that goes unnoticed or unrepaired and the humidifier just stops working. The solution to the germ issue is the addition of a UVC sanitizer light system that installs in the plenum-- the main ductwork near the furnace or heat pump air-handler-- and kills 99.9% of the living germs that fly past it. They cost about as much as the humidifier itself and the bulbs need to be replaced from time to time but they are worth it. I really don’t think a humidifier should be installed without the sanitizer lights. After doing that the thing you should be concerned about is the quality of the water going to the humidifier itself to prevent the works from getting gummed up with minerals. So much for the minuses There are all sorts and types of humidifiers out there but as long as you can control basic water quality and kill off the germs-- one’s good as the other. After installation they cost about as much as a couple of 60 watt light bulbs to operate and they only work when the air system is operating. And don’t forget to turn it off in the spring.