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If you live somewhere with cold, dry winters, like the U.S. midwest or east coast, you probably need a humidifer. Without one, your air is probably too dry for comfort and can cause little annoyances and health issues that I’m nowhere near qualified to discuss.

Almost nobody buys a humidifer that they’re happy with and that effectively humidifies the air. Below is what I’ve learned in my experience. First, a myth and a placebo:

• Steam-radiator heat, despite the popular misconception, does not automatically humidify the air with its steam. During normal operation, the steam is kept inside the radiators.
• Placing pots of water on top of radiators does humidify the air, but usually not by enough to matter unless you’re evaporating multiple potfulls of water a day. (I’ve never seen that happen.)

Remove the voodoo element: you should have something in your house that contains a hygrometer (a humidity meter) so you can tell when you need to use a humidifier and whether it’s working well enough. Many humidifiers have built-in hygrometers, as do some high-end thermostats and most digital indoor thermometers.

I suggest humidifying at least your bedroom, but ideally, you should humidify your entire house or apartment. Size matters: small humidifiers can’t humidify large areas. Humidity travels well between rooms, so one large unit can serve multiple rooms as long as the doors are kept open.

Now, the types:

• Central humidifiers that attach to your furnace are great. If you have forced-air heat, definitely investigate this option. I had one growing up, but I unfortunately no longer have forced-air heat.

• Steam humidifiers boil water and visible steam comes out. These are equivalent to boiling pots of water on the stove: they’re fairly quiet, but they use a lot of energy, and they can easily over-humidify a room and fog up the windows and walls.

  The air in a steam-humidified room never feels even or natural: it feels like someone just sprayed water into the air. (Which is basically the case.)

• Ultrasonic humidifiers effectively spray water into the air: they atomize the water into a fine mist that blasts out of a nozzle. Almost all of the cute animal-shaped humidifiers you see in stores are this type. If you hold your hand in front of it, your hand will be noticeably wet within seconds.

  These have most of the downsides of steam models: windows, walls, and even nearby floors get noticeably wet after a while, and the air isn’t evenly humidified. And they have another downside that doesn’t affect steam models: with ultrasonics, mineral deposits in the water get flung into the air, too, leaving many people complaining about “white dust” accumulating on surfaces.

• Evaporative humidifers contain fans that blow air through a wet wick-filter, evaporating the water at room temperature into the air. The air coming out of them isn’t noticeably moist and nearby surfaces stay dry. The fans make them the loudest type, and the filters need to be replaced regularly. But they humidify the air very evenly, they can’t oversaturate the air and therefore usually don’t cause condensation on walls or windows, and they’re usually available in much higher capacities than the other types.

I’ve owned at least one of each, and the only ones I’ve ever been happy with were evaporative.

For the last two months, I’ve used this huge Honeywell HCM-6009 to humidify the entire first floor of my house, and the highly regarded but very expensive Venta Airwasher LW25 in the bedroom.

The Honeywell is the workhorse: on recent dry days of about 20 degrees (F), it has evaporated up to 6 gallons per day (two full tank pairs). It’s not quiet enough for most bedrooms, but it’s quiet enough for the living room. I use one of these in the base (replaced monthly) and a capful of this in each tank of water to greatly reduce crap buildup in the base and filter. (The first month, I didn’t use them — they make a big difference.)

The Venta is very different. Rather than blowing air through a wick-filter, its fan blows down through a spinning multi-surface disk onto the water’s surface. This removes a lot of dust from the air, but the disk is difficult to clean, and you can’t dump the dirty water too often without wasting a lot of the required additive. The Venta is extremely quiet, though — this is by far its best feature. Unfortunately, with both humidifiers on their “medium” settings and all doors open, the Venta only evaporates 1-2 gallons on the same days that the big Honeywell is able to evaporate 6. The Venta doesn’t claim to be a high-output humidifier, but its low output and high price make it very difficult to recommend for anything but the smallest rooms with the most noise-sensitive occupants. It’s also disappointing that, at this price, it doesn’t have a hygrometer or an auto-shutoff feature to maintain a maximum humidity level.

If you need a humidifier, I highly suggest a basic evaporative model like the Honeywell HCM-6009. Just plan to buy some water additives and replace the filter once or twice per season, and it will humidify a hell of a lot more than a pot of water on the radiator.