Choosing a Furnace Humidifier

Before reading this page, you should review our page discussing the various types of furnace humidifiers on the market today. This should immediately narrow the range of options you are searching.

The following recommendations are based solely on my opinion. Before coming to my conclusions about furnace humidifiers, I completed a great deal of research into the topic, and have "experimented" with many models/styles over the years in trying to find the best solution for my family. I felt compelled to make this research available to others since most of the units found in stores today are simply a waste of money. This page will help you understand how I came to my decision and the reasoning behind ultimately recommending the model that I now have in my home.

drum humidifier problemUnless you are operating on a severely constrained budget, you should avoid all drum style humidifiers that come with an evaporative sponge or pad. They are inherently poor in design. The sponge/pad will inevitably lose its evaporative efficiency, especially in the presence of hard water minerals. Once the evaporative efficiency is lost, the water can stagnate and create a potential breeding ground for mold, bacteria, and other undesirable contaminants which can then be blow into your duct system and be distributed throughout our home. The only advantage of this style of furnace humidifier is that it is inexpensive. As inexpensive units, most models in this category are made with cheaper plastics that just don't seem like they will offer a long service life, although in my expereince, I could not test this since the drum/pad assembly became so troublesome to deal with after less than 2 years anyway. Some other models are still made with a metal reservoir and lid. When I first purchased my house, this is the type of unit that was installed there. Not only was it leaking, but it was horribly corroded. I have heard countless similar accounts about such models, so in my opinion, they should be avoided. All drum/pad furnace humidifiers will require periodic replacement of the evaporative sponge/pad. In extreme cases where there is a high mineral content in the water, the replacement interval can be as little as a couple of weeks. In one instance, I read on a home improvement forum of an individual who had to replace his after only a few days! In addition to the ongoing cost of replacing the evaporative pads, the nuisance of having to do so much maintenance also makes these units a poor choice.

Flow-through (flow-thru) are certainly an improvement in terms of cleanliness at least. One of the major drawbacks with flow-through units, however, is that they generally need to be connected to a floor drain system of other water discharge that will enable the excess water to be drained. This of course highlights the other major drawback of flow-through designs - they inherently waste a lot of water, up to 8 gallons of wasted water for every gallon of humidity output. This drawback can be particularly troublesome for homeowners with septic fields or limited production water wells, and those who pay for their water usage (metered residential systems). Of course, this level of water waste is not friendly on the environment either. Further, all flow-through furnace humidifiers will require periodic replacement of the evaporative screen - an added cost of about $20 per season. If you do not have a floor drain near the installation location, this option will likely not be available to you anyway.

poorly constructed drum humidifier poorly constructed flow-through humidifier
Here are 2 examples of poorly constructed humidifiers. Both of these are brand new. The bottom of the drum humidifier on the left clearly shows the cheap flimsey plastic used in the construction - the parts don't even line up right out of the box! This contributes to their low cost, but also short life and poor performace. When I was assembling this flow-through humidifier (picture on right) 5 minutes after opening the package, I broke the water distribution bar (not sure what else to call it). I had to order a replacement from the factory before installing it. Again, it was weak plastic and a poor design that led to the part failure. Be wary of low cost units!

Flow-through furnace humidifiers vary widely in cost. Cheaper models are typically built with light, flimsey plastic parts that don't hold up well over time. Nevertheless, there are some better units on the market in this category. Most of these superior quality units, while still suffering from the disadvantages mentioned, are at least a step above the drum/pad style humidifiers noted above. Aprilaire brand flow-through humidifiers are commonly sold through HVAC contractors and other building trades. While generally receiving fair to good reviews from most (but not all) homeowners, their cost after installation can run pretty steep.

rotary disc furnace humidifierIn the mid 1990's, a small company in Calgary, Alberta, Canada, (which has notoriously hard water), created a new humidifier design with a unique evaporative surface. Recognizing that a drum-style humidifier in concept had a lot of merits, they had set out to create an evaporative surface that did not suffer from the same problems as traditional drum/pad humidifiers. The company created an assembly composed of about 40 textured plastic discs that sit side-by-side (see picture courtesy of the manufacturer). The result was a highly efficient evaporative surface (with an impressive surface area), but an inherently cleaner design. The assembly proved to be resistent to excessive mineral build-up, thus it maintains its evaporative efficiency even when used with hard water. Hense, the water cannot stagnate, and the unit stays microbiologically clean. Like any good consumer, I was skeptical at first. However, when I bought the product (purchased online at, not only did I find it to be well built, but it really did stay much cleaner, and best of all, it does so with virtually 100% water efficiency - it doesn't waste water like a flow-through. The disc-assembly technology is patented, so at present they are the only company making this type of unit. Once or twice a year, I clean the disc assembly and basin with a light acid (vinegar) to remove the minor mineral deposits which mostly reside in the reservoir (I also recently installed the same company's AutoFlush accessory to further reduce my maintenance as I do have very hard water - so far, it has also met all of my expectations).

Regardless of what type of furnace humidifier is selected, a humidistat is essential to maintain humidity control. Avoid any unit that does not have a humidistat included. Also, some manufacturers fail to include all required installation parts with their unit - you could get an unpleasant surprise when you have to buy flex duct, water line, saddle valves, mounting hardware, screws, bolts and other items to complete your installation. These added costs can turn an inexpensive unit into an even bigger disappointment.

One final note, if you have a heat pump instead of a conventional electric or gas furnace, talk to your supplier before purchasing as many models do not operate as efficiently with the reduced output temperature of a heat pump. A good supplier can offer you some recommendations to boost air flow to your unit to help compensate.