Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: how often do you clean them?
Document: We also had a regular cool-mist wick humidifier, but the water in that also got gross pretty quickly, unless you washed it out with soap each night. This one stays clean for months at a time. I recommend changing the filter at least every 2 months, and a lot more often if you have pets.
I bought one of these to humidify the air in our master bedroom because the ultra-dry air in southern Arizona (the relative humidity often is in single digits) was wreaking havoc with my sinuses. Within a few days it had raised the humidity in the good-sized room to a comfortable 40-45%. The unit seems well-constructed and is easy to refill and clean.
The materials of this unit are a solid plastic that is hydrophobic, so it's easy to clean. I haven't put it in the dishwasher, but I understand that you can. The high speed fan is a bit loud for our bedroom, but we don't leave it on high because the water doesn't last the rated 24h at that speed. There is no low water cut-out on the fan, not a huge deal, but the filter/evaporator mesh gets crusty if it runs dry too often.
Does not leave any white or chalky residue all over our bedroom as did our previous humidifier. Only down side, is that this one has a smaller reservoir, so it needs to be filled a bit more often than previous model we had.
This unit is very quiet when it is running. The water well is easy to carry even when full. I just don't like having to fill the water well so often but otherwise I am pretty happy with the humidifier.
we bought this to replace our old humidifier that was not working properly. it is much more quiet and does not put out so much humidity that the carpet is soaked like our old one did. I like how this one is much easy to fill- the water container is a bit smaller but that does not seem to affect how often it needs to be refiled. it is a more sleek design and easier to put out of the way.
The humidifier works ok but the filters get very stiff and coated with minerals quickly unless you use soft water. I live in a place that uses spring water, not a good choice for this humidifier. If you have soft water than maybe it will work great for you. Any of the misters or humidifiers that use a paper filter will need to be changed often or you will not get any humidity from them.
It will NOT humidify an entire house, but may do the job for a small apartment. I would definitely recommend this unit to friends. The filter needs to be replaced periodically as minerals from your tap water will accumulate with time. The filter life can be extended by soaking it in vinegar and rinsing it out once it gets "limed up". The filter will still need to be replaced with this cleaning method, but not as often.
We purchased this for our bedroom. We recently moved to a home with hot air heat and I had no idea how drying that can be. Since this has been such a cold winter the dryness has been difficult for me. I purchased this humidifier and it's help at night while we sleep to keep the air more moist. I think they need to warn about changing the filter more often then they say because I checked the filter after a few weeks and it was really gross.
Our house a steam heat and so we bought this for the bedroom. Except on the high setting, the fan is pretty quiet, but the tank bubbles (like a water cooler) quite often and that is really distracting in a dark, nearly silent room. The dog won't sleep in there anymore. Also, the tank is really small; it lasts about 12 hours. It's very easy to refill, but its still a hassle to have to do it so often.
Answer: Typically, we'll clean the filter/pad about once a month (during the season) by rinsing it out. For each new season, we purchase a new filter/pad...as they tend to harden over time; particularly if you have hard water. Also, take a dampened cloth over the exterior and interior to remove any water scaling is helpful. Hope that helps...