You want your home to smell amazing. The problem is, as soon as you start looking for a diffuser online, you discover three totally different kinds of product — all branded as “diffusers” — that work completely differently to produce completely different results.
Reed diffusers. Ultrasonic diffusers. Cold air diffusers. 

Prices range from $99 all the way up to $500+. The range of scent experience covers an even wider spectrum. In this complete guide, we break down exactly how each type works, what you can expect from each option, and help you pick the right diffuser for your needs.

Reed Diffusers: Passive, Simple & Limited 
A reed diffuser is perhaps the simplest way to scent your home. A glass vessel is filled with fragrant oil, then a bundle of porous reeds is inserted. The reeds soak up the oil and release fragrance passively into the surrounding air through capillary action.

What they're good for: 
Simple, low maintenance, doesn’t require power. Reed diffusers work well in bathrooms, hallways and bedrooms. They’re also aesthetically pleasing objects themselves that suit stylish interiors.

Where they fall short: 
The throw from a reed diffuser is very limited. In open-plan living / dining spaces — think large, high-ceiling living areas like you’d find in a typical Australian house — a reed diffuser simply cannot cover the space. You’ll smell it when you’re standing next to it, but it won’t scent the room in the way that transforms the mood and feel of your home.
Reed diffusers also offer no control. There’s no way to turn them up or down, schedule when they turn on and off, or adjust intensity. If it’s on, it’s emitting fragrance continually whether you’re home or not. Which means you’re wasting oil whenever the house is empty and it’s doing nothing for you.
Best for: Small rooms, bathrooms, hallways, or as a stylistic accessory to supplement a more powerful primary diffuser.

Ultrasonic Diffusers: Popular, Affordable & Compromised 
Ultrasonic diffusers are currently the most widely sold diffuser type in Australia. These devices utilise a water reservoir, which you add a few drops of essential oil to before activating high-frequency ultrasonic vibration that disperses the mixture as a fine mist into the surrounding air.
You’ve probably seen one in action. They’re everywhere: budget-friendly, supported by the majority of major retailers, and the mist they produce as they work looks cool. Chances are if you’ve ever used a diffuser before, it was ultrasonic.

What they're good for: 
Cheap entry points into home scenting. They’re easy to use and double as a humidifier if you’re looking to add moisture into the air.

Where they fall short: 
Ultrasonic diffusers dilute your fragrance BEFORE it ever reaches the air. When you mix oil with water, you’re watering down the scent. This means that the mist emitted into the air is a weak version of the fragrance oil you started with. Top notes, complexity, depth — you lose much of it.
Speaking of water… they also release moisture into the room. In summer here in Australia, or any humid climate, that’s the last thing you want. And over time, the mist will leave a fine residue on furniture, artwork and even your electronic devices.
Coverage is another weak point. Ultrasonic diffusers are typically designed to cover up to 20–30 square metres. Your average open-plan kitchen and living space is somewhere around 70–90m² (the standard in most new Australian homes). To get enough presence from an ultrasonic diffuser to smell it upstairs you’d need several units working constantly, and the whole house would still smell weak compared to other options.

Best for: Budget buyers, bedrooms or those just looking for a basic scenting experience.

Cold Air Diffusers: The Technology Found in Five-Star Hotels 
Also known as nebulising diffusers or waterless scent diffusers, cold air diffusion works on an entirely different principle than the other types. Instead of diluting oil with water, they use pressurised streams of cold air to propel pure, undiluted fragrance oil into the air as an ultra-fine dry mist.

That dry mist contains billions of nano-sized fragrance particles. But because they’re dry, where they land doesn’tmatter.That desk your kid spills everything on? Those heaters in the corner? That expensive sofa you bought from brunch? None of it matters. Cold air diffusion will scent your home without damaging any of your belongings.

They’re also commonly used in hotels. Hotels that don’t want their guests to notice the scent, but notice it when they leave.

What makes cold air diffusion different: 
Full Strength Fragrance. The oil is not diluted before it’s dispersed. That means every complex note your fragrance has to offer — from bright citrus top notes, to spicy middle notes, to warm woody base notes — is richly represented when it hits the air.
Coverage: Cold air diffusers are built to cover large spaces. Our Ascent Collection diffusers cover anywhere from 100m² up to 5,000m³. That’s small bedrooms all the way up to commercial venues. One can easily scent an entire home. 
No humidity, no residue. Once the mist settles, there’s no moisture left behind on any surface. Cold air diffusion will not leave your furniture looking cloudy, your artwork covered in wet spots, or your room feeling humid.

App control & scheduling. Our whole line of Ascent Collection cold air diffusers feature Bluetooth or Wi-Fi enabled controls that connect to your phone. Set intensity, create schedules, and even programme the diffuser to turn on up to five separate times per day at varying intensities. That way your home smells amazing whenever you walk through the door without having to run it all day long.

Safe for kids, pets, and your art collection. Unlike other types of diffusers that use heat or water to disperse fragrances, there is zero risk of burns or spills with cold air diffusion. Plus, all Ascent Collection fragrance oils are IFRA compliant and use only fragrance grade ingredients — meaning they’re free from any harmful chemicals.

What they cost: 
Compared to ultrasonic diffusers, cold air diffusers do represent a higher upfront investment. But as you’ll learn from our reviewers below, the experience they create, quality of build, longevity of the hardware, and amount of control you have over your scenting makes them an entirely different category.

Best for: Anyone that wants their home to smell like a luxury hotel. We can’t recommend highly enough the impact that cold air diffusion can make on your home. If you’ve ever entered a gorgeous hotel lobby and wished your home smelled that way, now you can.
Side-by-Side Comparison 

Reed DiffuserUltrasonic DiffuserCold Air DiffuserScent strengthLowMediumHighCoverageUp to ~20 m²Up to ~30 m²Large spacesLowest water contentFull fragranceFragrance qualityPassiveDilutedAtomicDry mist adds to humidity?NoYesNoMesses on furniture/artwork?MinimalPossibleNoTechnologyMost commonWhy we think you should pick itSmart, affordable option for small spaces.Controls water content of your fragrance.Every luxury hotel Loves itBest forSmall rooms or spaces on a budget.Budget conscious home scenters.Anything. Seriously. 

Which Diffuser Should I Choose? 
If you’re looking for a low maintenance fragrance boost for a single room — like a bathroom counter or a bedside table — go with a reed diffuser. They won’t scent your whole home, but they’re beautiful pieces that can really tie the look of a room together.
Got a tight budget? Ultrasonic diffusers are a great way to get into home scenting. Just know that by choosing water based ultrasonic diffusion, you’re accepting a watered-down version of what your fragrance can actually offer.

Want your home to smell like a five-star hotel?? Welcome to the club. Cold air diffusion is the secret hotels don’t want you to know. Every “premium” scenting experience you’ve ever walked into uses one of these bad boys. And now you can have them for your home too.

Ready to Try Cold Air Diffusion For Yourself?
Ascent Collection’s range of cold air scent diffusers starts at the Scent Mini for bedrooms and upsmaller spaces all the way through to our commercial grade S3,000. Every model is app-controlled, whisper quiet, and compatible with our growing range of IFRA-compliant fragrance oils.
That includes our signature Hotel Collection scents, designed to match the relaxing scent journey of the world’s most luxurious hotels.

Shop all diffusers → 

Commercial scent diffusers for hotels, offices, spas →