humidifier-shootout (18K)
Humidifier Shoot-Out

Air-O-Swiss AOS 7135 vs. Venta-Sonic VS 207

by Carson Wilson

Last update: 02-Dec-2009 03:04 PM

I created this web page because these are the quietest small room humidifiers avaliable, but I found conflicting reviews of the Air-O-Swiss 7135, no reviews of the Venta VS 207 online, and that both models consistently underreport ambient humidity. The Venta VS 207 is apparently new enough that nobody has reviewed it, and the Air-O-Swiss seems to give different results to different users, perhaps due to manufacturing inconsistencies. Also note that the frequently cited Allergy Buyer's Club is a vendor of Air-O-Swiss brand only, which may be why they omit Venta from their reviews.

Online Manuals

Venta-Sonic provides an online manual for the VS 207 in PDF format here.

I have been unable to find an online manual for the Air-O-Swiss 7135, so I am furnishing one here. However, I did find an online site for the 7135 by its manufacturer, Plaston AG.
At a Glance Comparison (advantages in green)

Air-O-Swiss 7135 Venta VS 207
Price $150 street $150 street
Capacity 2 gal 2 gal
Humidity level control range 40-75%, constant 30-60%, constant
Humidity level control increment 5% 5%
Output levels 4 3
Warm mist Yes Yes
Antibacterial silver Requires separate $30 silver stick yearly Silver built into filter cartridge
Replacement cartridge cost $12.50 $14.99
Cartridge refill pack $19.99 for three resin refill bags Not available
Cartridge pre-soak time 24 hours Several minutes
Cartridge replacement interval 2 to 3 months 2 to 3 months
Warranty 3 years 1 year
Controls Warm/Cool, Output Level, Target Humidity, Timer, Sleep, Auto Warm/Cool, Output Level, Target Humidity
Settings Retention None All but output level
Manufacturer Location Switzerland USA
Country of Manufacture Korea Korea
Dimensions 15.2 x 8.8 x 13.8 in 13 x 10 x 13 in
Cable length, color 72 in, black 72 in, white
Weight (empty) 7 lb 8.4 lb
Serial number of sample 051208003 KK1L716358N

Noise Level

This is an area of interest as smaller humidifiers are often used in sleeping areas. Depending on background noise levels, even a very quiet motor sound may disturb sleep. Both the AOS and the Venta employ an electric fan to distribute humidified air and therefore do generate some fan noise. Claims that they are completely silent are exaggerated, although even soft background noise such as urban street sounds or a running furnace will render them inaudible. However, I can hear the AOS from across my quiet suburban bedroom, and in fact both units make a very soft 60 cycle hum even when powered off (but still plugged in). This sound is about as loud as the motor in an electric clock.

Both models have well damped motor noise, but the Venta is significantly quieter than the AOS.

Here are sound recordings of both models. Both units were running at their highest output settings with tanks 1/2 full. The sound was sampled using identical recording settings from floor level, about 3 inches from the front center of each unit. I've included identical background music (John Coltrane's Summertime) to give you a consistent frame of reference:

Contrary to some reports, both of the models in my sample generate periodic gurgling sounds as air enters the water chamber through the valve which admits water to the humidifier base. The Air-O-Swiss seems to gurgle more softly, but this may only seem so because of its generally higher noise levels.

The Venta makes a disturbing solenoid click when turning its oscillator on and off as the detected ambient humidity climbs above and falls below the user setting. The humidity gauge is sensitive enough that this can occur several times per minute once the selected humidity level is reached, even at the lowest output setting. This may also be the case with the AOS but I just haven't noticed it due to the AOS' higher overall noise level.

Settings Retention

This is a key difference. The AOS 7135 can be programmed for output level, target humidity, timer, warm/cool, and sleep and auto modes. However, all of these settings are lost whenever the unit is powered off with its on/off switch. Whenever it is powered on, the AOS reverts to its "auto" mode. On the other hand, the VS 207 retains all settings EXCEPT for output level, which reverts to maximum when the unit is powered off with its on/off switch.

Both models lose ALL program settings when unplugged (which must be done prior to cleaning).

If you power on the Venta when empty, it will flash its display until enough water has been added for operation, at which point it will return to operation. If you've unplugged it, it will run at its highest output level continuously. Under these conditions, I recall that the AOS simply powers off after a brief period (please email me if not).

Hygrometer Accuracy and Range

humidifier-humidiguide (51K) Another key difference: my sample of the AOS 7135 consistently reported a significantly lower relative humidity than either the VS 207 or my Taylor HumidiGuide operating in the same location (about $10. I highly recommend a HumidiGuide as a more accurate and reliable gauge than either of these humidifiers'). The photo to the left was taken after both humidifiers had run for several minutes. Notice the humidiguide's reading of about 55% versus the AOS 7135's reading of 25% and the VS 207's reading of 43%. Additionally the AOS 7135's lowest desired humidity setting at 40% is 10% higher than the VS 207's lowest setting.

Both models indicate humidity levels at least 10% lower than my Taylor HumidiGuide. I suspect the Taylor is more accurate than either humidifier as a) the readings of all Taylor HumidiGuides in the rack I purchased it from were identical, and b) 50% relative humidity as measured by either humidifier feels quite damp, whereas at 50% (the level recommended in both manuals) on the Taylor the room feels properly humidified. I also observed this with the AOS 7135 and Venta VS 207's on display at my dealer, so it's not limited to my sample. I am surprised at this and can only speculate that the low readings are designed to compensate for slow circulation in large rooms, where a high humidity reading near the unit would translate to a normal reading across the room. In a small room both of the units I sampled overhumidify when set to 50%. The AOS will raise humidity to well above 50% when set to its lowest setting of 40%, so my strategy with it is to set its timer to avoid this occurring overnight. With the Venta I set the desired humidity to 40%, resulting in actual humidity levels of about 50%.

Further note: AllergyBuyersClub says " We recommend that indoor humidity levels in winter should be around 30 to 40%." This may be a significant concern about the AOS 7135 as the lowest setting it provides is well above 50% (when it is set to 40%).

White Dust

Both models claim to have eliminated "white dust" through the use of demineralization cartridges. However, I find they both still produce some white dust (actually it is light grey in color) even when the cartridges are new. This is with my city water which is neither excessively hard nor soft. Also, both models recommend changing the filter cartridge when white dust appears, several times per season. So there is no total guarantee against white dust, just that the filter cartridge greatly reduces it (until it doesn't). The only total guarantee against white dust is an evaporative humidifier (the new Slant-Fin with mineral-absorption pads is probably the best), but these are significantly louder than ultrasonics due to boiling noise. Personally, I have not found the dust a problem after several months of use.

Placement in Room

Both models come with instructions to place them on a raised surface as failure to do so may may cause water to accumulate on your floor or carpet. I make no promises, but my experience so far is that they may be placed on a hard surface at floor level in a standard bedroom at room temperature so long as the warm mist setting is used with the lowest output setting. A hard surface must be used in order not to block the air inlets in the base.

Cleaning Indicator (AOS only)

The Air-O-Swiss 7135 includes a cleaning indicator lamp which continues to flash red until the lamp is reset by holding the on/off switch for several seconds. This apparently is not a true indication that any cleaning is needed but is rather activated by a timer that accumulates wall clock time since the last time the lamp was reset. This is my conclusion as the lamp comes on when the oscillator is not dirty (or even running) and does not turn off until reset, at which point it does not come back on again regardless of whether the oscillator has been cleaned.

When to change the filter cartridge?

Both units recommend changing the cartridge every several months or as needed, and apparently "as needed" is when you notice white dust (the AOS Manual on page 12 indicates "Demineralization cartridge exhausted" and recommends you "Replace cartridge or granules" to remedy the problem of "white around the humidifier"). As noted in the table above, the Venta requires purchase of a new filter cartridge while the AOS allows cartridge refilling. This saves some money but is made up for by the need to replace the AOS' $30 silver stick annually: e.g., replacing or refilling the cartridge every 10 weeks during a 5-month season:

Final Words

My overall advice: if you think you might want a quiet humidifier for your bedroom,