are the cheapest, easiest to install, and most water efficient (they don’t require a floor drain and they put 100 percent of the moisture used into the air). But, the drum style reservoir allows for the buildup of mold, minerals, and bacteria which can make it a poor choice for severe allergy sufferers. This also means cleaning the unit as frequently as once a month. Drum style humidifiers have an evaporator pad/sponge on a drum that rotates by means of small motor, dipping itself into the water reservoir and wetting the pad/sponge, when your humidistat senses that you need more humidity. The heated air from your HVAC system passes over this and brings moisture into your home. This pad/sponge needs to be replaced at least once per year, sometimes more frequently.
can be more expensive and complicated to install as they require a nearby floor drain. They are also less water efficient than drum style humidifiers (because for approximately every one gallon of output there are two gallons of waste water). Bypass or flow-through humidifiers have a vertical evaporator pad that is wetted with water by means of a connected water valve that opens when the humidistat tells it to. The air from your HVAC system passes over this pad and brings moisture into your home. There is no standing water and the pad is continuously flushed through with fresh water, so these units typically only need cleaning about once a year, which is about the same timeframe for replacing the pad. Some newer flow-through humidifiers have a “pulsed” water supply that uses less water.
can be mounted either directly onto your HVAC system or nearby with a tube running the steam up to where it is dispersed. Installation requires a nearby regular or higher-rated electrical outlet depending on the size of the unit, and a floor drain or condensate pump (usually found beside your furnace). Steam humidifiers use the least amount of water of any humidifier and there are no pads that need replacing. They simply boil water to create steam and this steam is then carried by air from your HVAC system into your home. Steam humidifiers are the fastest type of humidifier on the market but are also the most expensive to buy and install. There is virtually no bacteria growth and the unit requires only once a year cleaning with regular soap and water. Steam humidifiers typically come with mineral water filters that need to be changed once a year.