I have the HD15 how do you clean it latly everything is covered in a chalky mist in the room?

All question need full 'make model (what it is)' to answer efficiently.

Some actually spay a mist of water, but the better one suck dry air in and blow moister air out through the saturated filter membrane.

The ones that spray water mist damage furniture and anything near it. If it is the spray type, it needs descaling.

You could Google

make model manual

Or list it under her by clicking Comment under _my_ answer.

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When going to buy a humidifier always check these points:
Technology used: Ultrasonic is good and inexpensive
Performance: The area it covers
Features: Does it offer both cool mist or hot mist
Design: compact and sleek design
customer support: The process of servicing and maintenance etc.
Read these top humidifier reviews to get the best
GroomNStyle Top 5 Best Humidifiers 2015

If there is water in it, it sounds like the ultrasonic unit failed.

it has a quiet operation when you got it brand new did it put out mist

My Guess is that the reletive humidity in the room is not low enough to see any vapors coming from the machine. Normaly you won't see these anyway. Some models in the stores seem to make more mist than what you get at home. If the humididty level in a room is close to what is coming out of the machine there will be no signs of any mist coming out. Just make sure the filters are clean and check and make sure the water level is going down on the machine and this will tell you its workin. the faster you are using the water in the tank the more you are putting in the air! If this is a hot mist machine then I would say the heating element in the machine is not working.

i would try cleaning the coils for the heat portion. if they are to scally that could be one reason why it's not making any mist. but if it looks pretty clean or if you have cleaned it and it's still not making any mist then it's something internal. now if your under warranty still that's a good thing. you can always call the manufacturer and they can replace theunit for you under warranty . if you have any other questions please let me know.

Located My Manual:
Hope this helps!

1. Remove tank from base. Turn upside down and unscrew filling cap. Fill tank with clean, cool, distilled, or tap water. Water temp should NEVER be too hot or too cold. Return tank to base and let sit for a few minutes. Be sure the filling cap of the tank is tightened firmly.

2. Plug power cord into a 110-120V AC wall outlet only. Turn power switch to "on" position. Power light will illuminate. Turn mist nozzle until desired level is being released. Aim nozzle away from furniture and walls.

3. Always turn humidifier off when water runs* out. Unit will continue to operate when tank is empty.
*Humidifier will run up to 12 hrs on low; 6 hrs on high.

DO NOT LET WATER SIT IN TANK FOR LONG. THIS CAN ENCOURAGE BACTERIAL GROWTH.
Place unit on level surface away from direct sunlight.
DO NOT ADD MEDICATION OF ANY TYPE INTO THE NOZZLE, BASE, OR WATER TANK.
ALWAYS LEAVE ROOM DOOR PARTLY OPEN. DO NOT MOVE, TILT, OR EMPTY WHILE OPERATING.

Mild bleach and water solution for cleaning, never detergent.
Clean every 3rd day during use. Clean after long storage
Humidity varies from room to room. Aim for 30 - 50% relative humidity. If windows/ walls fog or frost, reduce mist intensity. If room too humid, ventilate by opening door or window; adjust mist intensity.

I haven't had any problems with my Vicks Cool Mist Humidifier other than the fact that the area surrounding it is slightly wet after operating for a couple of hours....While I understand that I was using this to moisturize the air during a cold, I knew this would happen, because the air in my room is not dry. If the room isn't dry, the mist that it's putting out in to the air has no where to go but surround the humidifier. All I did to stop this was to buy a water proof mat. I suggest you do the same -- Also, in regards to the water smelling -- You should be cleaning out and drying the basin after every use. Water shouldn't smell unless you let it stagnate inside the plastic -- Try running distilled vinegar through the machine for a couple of minutes -- Also, I would use an extension cord and let it run outside so that your house doesnt smell like Vinegar.