My home is about 3000sqft, with lots of high ceilings.

I'm having trouble keeping the relative humidity up in the winter. When it gets down to 10F outside, the RH drops down as low as 25%. This is WITH a bypass humidifier installed. (filter new, water flow seems good).

Have read that many people have similar experiences with evaporative bypass humidifiers. They just can't add enough humidity to keep up.

The only solution so far is either 1) Honeywell TrueSTEAM, 2) Aprilaire 800 steam humidifier.

I understand that these steam humidifiers use quite a bit of energy in generating the steam. They also seem expensive and some of them unreliable.

My proposed setup is this: 1) Reverse Osmosis water filtration system ($150-200), 2) High output ultrasonic fogger/humidifier ($50-100), 3) Small fan ($10). The output of this would be piped into the current bypass humidifier housing.

Why hasn't something like this been done yet? It seems like the biggest hurdle for ultrasonic humidifiers is the white dust / vaporized minerals in the water. Any HVAC professionals that could comment on this sort of setup? I surely don't want to ruin my furnace.

  • 1
    Chris, I'm wondering if you ended up doing anything with this ultrasonic idea. I've been thinking of doing the same thing. Gary.
    – Gary Smith
    Commented Jan 9, 2017 at 2:25
  • I concur. Why not a simple device you insert into the furnace with a flow sensor that has a plug and water input with a descale and replacement ultrasonic plate cartridge. This should be so easy and cheap if it worked.
    – Jeff Basso
    Commented Jan 17, 2017 at 19:11

2 Answers 2


I've thought the same but think you want a fairly big fan. You are fighting to keep the ultrasonic droplets from condensing on surfaces. You need to supply enough air flow for them to evaporate and not condense. Position the output somewhere where a dribble caused by condensation won't wreck a motor or electronics


The first problem, is that the ultrasonic humidifiers don't remove impurities or pathogens from the water. Which can lead to lowered indoor air quality, and negative health effects.

Another problem, is size. The typical desktop sized ultrasonic humidifier, is only designed to humidify a few hundred square ft. You'd need quite a large unit to humidify an entire home, at which point it may be cost prohibitive.

They do make humidifiers that spray a fine mist into the ducts, though I believe the droplets are a bit larger than those produced by an ultrasonic unit. They likely have the same problem as an ultrasonic, as they won't remove water impurities or pathogens either.

Steam humidifiers are likely the "safest" choice when it comes to air quality, as they'll remove most impurities and kill pathogens. However, they use more power, since they have to turn water into steam.

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