The Levoit OasisMist 450S and DREO HM311S are two smart ultrasonic humidifiers with similar tank capacities, plenty of advanced features, and attractive designs.
However, there are some significant differences between them.
The Levoit OasisMist 450S is a hybrid ultrasonic humidifier that can produce cool and warm mist. It has a 4.5 L tank, is designed for rooms up to 430 sq. ft. (40 m²), and delivers one of the best results of all humidifiers we’ve tested.
The DREO HM311S is a more compact cool-mist humidifier with a 4 L tank and a recommended room coverage of up to 300 sq. ft. (28 m²). It isn’t as powerful as the Levoit, but it has an impressive runtime, operates very quietly, and comes with plenty of smart features.
I tested both humidifiers under the same conditions, so let’s see how they compare and which one is the better buying option.
Our Verdict
After comparing their specifications, features, and all the test results, the Levoit OasisMist 450S is the winner of this comparison.
The biggest reason is performance. In our 194 sq. ft. (18 m²) test room, the Levoit increased the relative humidity by 16.9 percentage points in 60 minutes, while the DREO increased it by 12 percentage points.
The Levoit was also much faster. It needed only 11 minutes to raise the humidity by 5 percentage points, compared with 18 minutes for the DREO.
It also has a higher moisture output, covers larger rooms, offers cool and warm mist, and achieved a much higher overall rating in our tests. That doesn’t mean the DREO HM311S is a bad choice.
In fact, it has a few advantages. Its tank lasts significantly longer at maximum speed, it uses slightly less electricity, it’s extremely quiet, and I think its design and night light are among the best I’ve seen on a humidifier in this price range.
But if I had to choose just one, I would go with the Levoit OasisMist 450S. It simply does the main job of a humidifier better, which is increasing humidity quickly and effectively.
The DREO makes more sense if you want a cheaper, compact humidifier for a bedroom or smaller room and value long runtime over raw humidification performance.
Specs: Levoit OasisMist 450S Vs DREO HM311S
| Product Image |  16% off |  15% off |
| Manufacturer | Levoit | DREO |
| Model | OasisMist 450S | HM311S |
| Type | Hybrid-Ultrasonic | Ultrasonic Cool Mist |
| Dimensions (inches / cm) | 10.8 x 6.0 x 11.97 inches (27.4 x 15.2 x 30.4 cm) | 11.02 × 5.51 × 10.16 inches (28.0 × 14.0 × 25.8 cm) |
| Weight (pounds / kg) | 5.3 lb (2.4 kg) | 3.12 lbs (1.42 kg) |
| Coverage | 430 sq. ft. (40 m2) | 300 sq. ft. (28 m2) |
| Tank Capacity | 4.5 L | 4 L |
| Humidity Sensor Humidity Sensor Summary: Out of 9 humidifiers tested, only 5 have a built-in humidity sensor. | Yes | Yes |
| Smart App Smart App Summary: Out of 9 humidifiers tested, only 5 have smart app functionality. | Yes | Yes |
| Auto Mode Auto Mode Summary: Out of 9 humidifiers tested, only 5 have auto mode functionality. | Yes | Yes |
| Filter | Yes (Water Filter Sponge) | No |
| Other Features | Aroma DiffuserNight LightSleep ModeAuto Shut Off | Night Light |
| Efficiency Test Efficiency Test Score Summary: 8 - Average Score (9 products) 9.5 - Best Score (2 products) 6.7 - Worst Score (1 products) We test the humidity output of every humidifier in a 194 sq. ft. (18 m²) room over a 60-minute period at each fan speed. Relative humidity is measured with the GoveeLife Hygrometer and additionally verified with a TempPro hygrometer. You can read more about our testing methodology here. | ||
| Runtime | 15 h | 19.5 h |
| Moisture Output (Max Speed) | 301 mL/h | 206 mL/h |
| Power Consumption
Power Usage Summary: Our extensive testing of 9 humidifiers revealed the following power consumption insights:
Check out our power consumption calculator tool. | 280W | 26W |
| Operating Costs Ratings Operating Costs Ratings Score Summary: 8.6 - Average Score (9 products) 10 - Best Score (1 products) 4.4 - Worst Score (1 products) We measure the power usage at all speeds using an energy meter, after which we calculate how much it would cost to use the device at a particular fan speed for one month. For reference, we use an energy price of $0.12 per kWh. You can read more about our testing methodology here. | ||
| Best Suited For | Large Spaces Plants Dry Skin Allergies Smart Home Integration | Small Spaces Quiet Operation Bedrooms Low Energy Cost |
| Warranty | 2-year | 1-year |
| In-Depth Review | Levoit OasisMist 450S | DREO HM311S |
| Price |
Humidifying Performance – Comparison
Performance is where the biggest difference between these two humidifiers becomes clear.
We tested both devices in the same 194 sq. ft. (18 m²) room.
Before each test, we used a dehumidifier to lower the room humidity to around 40% RH. We then ran each humidifier at maximum speed for 60 minutes while monitoring humidity using the Govee Hygrometer H5075, with a ThermoPro meter used to verify the readings.
The Levoit OasisMist 450S started at 40.3% RH and increased the humidity to 57.2% RH after 60 minutes. That’s an increase of 16.9 percentage points.
The DREO HM311S started at 40.7% RH and increased the humidity to 52.7% RH, an increase of 12 percentage points.
The difference becomes even more obvious when looking at how quickly they raised the humidity by 5 percentage points.
The Levoit needed only 11 minutes, while the DREO needed 18 minutes.
That’s quite a large difference.
The Levoit also used around 300 mL of water during the test, while the DREO used approximately 206 mL. In other words, the Levoit releases considerably more moisture into the room, which explains why it was able to increase the humidity much faster.
I would say this is the most important difference between these two models.
The DREO HM311S performed well, especially considering its size and price, but the Levoit OasisMist 450S is in a different class when it comes to humidifying performance. The Levoit is the clear winner in this test.
Water Consumption & Runtime – Comparison
This is one category where the DREO has an advantage. The Levoit has a slightly larger 4.5 L tank, compared with the DREO’s 4 L tank.
However, because the Levoit has a much higher moisture output, it also uses water much faster.
At maximum speed, the Levoit consumes approximately 300 mL of water per hour, which gives it a measured runtime of around 14.9 hours on a full tank.
| # | Levoit OasisMist 450S | DREO HM311S |
|---|---|---|
| Tank Capacity | 4.5 L | 4 L |
| Water Consumption | 300 mL/h | 206 mL/h |
| Runtime at Max Speed | 14.9 h | 19.5 h |
The DREO consumes only about 206 mL per hour, allowing its smaller 4 L tank to last approximately 19.5 hours at maximum speed.
So, the DREO lasts around 4.5 hours longer on a full tank even though its tank is 0.5 L smaller. That sounds like a big advantage, and in some situations it is. However, there is an important trade-off.
The DREO lasts longer because it outputs considerably less moisture. The Levoit uses more water because it humidifies the room much faster.
Personally, I would rather have higher moisture output and refill the tank slightly more often, especially if I were using the humidifier in a very dry or larger room.
Both models use a top-fill design, so refilling them is easy anyway.
Still, if runtime is your priority, the DREO HM311S wins this category.
Operating Costs – Comparison
There isn’t a huge difference between these two models when they are used as cool-mist humidifiers.
The DREO HM311S is rated at 26W. Running it continuously at maximum speed for 24 hours a day would add approximately $2.18 per month to your electricity bill, assuming an electricity rate of $0.12 per kWh.
The Levoit OasisMist 450S consumed 27.4W at maximum speed in our test. Under the same conditions, it would cost approximately $2.40 per month.
The DREO technically consumes less electricity, but there’s another metric that I find more interesting.
The Levoit produces approximately 11.0 mL of moisture per watt-hour, compared with 8.3 mL/Wh for the DREO.
So even though the DREO uses slightly less electricity, the Levoit actually converts the electricity it uses into moisture more efficiently.
| # | Levoit OasisMist 450S | DREO HM311S |
|---|---|---|
| Max Speed Power Use | 27.4W | 26W |
| Monthly Cost at Max Speed | $2.40 | $2.18 |
| Moisture Efficiency | 11 mL/Wh | 8.3 mL/Wh |
There is one major exception.
The Levoit also supports warm mist, and when this feature is enabled at maximum speed, its consumption jumps to 279.4W. That is more than ten times its cool-mist consumption.
I don’t see this as a major drawback because you don’t have to use warm mist, and I imagine most people would use it only occasionally, probably during colder months.
If we compare the two primarily as cool-mist humidifiers, the difference in monthly electricity cost is negligible.
Cleaning & Refilling – Comparison
Both humidifiers have a top-fill water tank, which makes everyday refilling straightforward.
The Levoit OasisMist 450S is easy to disassemble, but cleaning it takes a little more time. I found that you should expect to spend around 10 to 15 minutes actively cleaning it, especially if mineral deposits have started to build up.
The DREO HM311S is also easy to take apart, and most surfaces can be cleaned using a soft cloth.
Neither model is something I would recommend putting in a dishwasher.
With both devices, I would also avoid tap water if possible.
This is particularly important with ultrasonic humidifiers because minerals in hard water can build up inside the device and can also end up being dispersed into the room as white dust.
I wouldn’t say there is a major difference between these two when it comes to everyday maintenance.
Both are easy to refill, both require regular cleaning, and neither has a design that makes maintenance unnecessarily complicated.
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