Air Purifiers and Dust: What They Can Do (and What They Can’t)

Choosing an air purifier can feel overwhelming. Every brand highlights different features; sensors, modes, filters, apps. However, not all of them actually improve your air quality in a meaningful way. At its core, an air purifier does one job: move air through a filter and remove particles. How well it does that depends far more on airflow and filter quality than flashy features. This guide breaks down the features that genuinely matter when choosing an air purifier for NZ homes. We'll also show you where it’s easy to be misled by specs that look good on paper but don’t translate to cleaner air. Table of contents 1. HEPA Filtration: The Foundation of Clean Air 2. Carbon Filters: Odours, VOCs & Why Weight Matters 3. CADR: The Most Important Number on the Spec Sheet 4. Sizing a Purifier Properly: CADR, Room Size & Noise i. Why Manufacturer Room Size Claims Can Be Confusing ii. Noise levels: What to look for in real use 5. Extra features: what to be cautious of (and why) Ionisers (negative ion/plasma modes) UV Lights Auto modes and built-in sensors Wi-Fi and app control (nice to have, not essential) 6. Wrap-up: Focus on the simple features Looking for an air purifier that ticks all the boxes? Quick guide: what actually matters HEPA filtration matters more than fancy features CADR (airflow) is the most important performance number Room size claims vary, CADR makes comparison easier Bigger units can run quieter on lower speeds Carbon filters only help if they use real carbon pellets Ionisers and “active” tech often add complexity, not performance 1. HEPA Filtration: The Foundation of Clean Air HEPA filtration is the most important part of any effective air purifier. A HEPA filter works by physically trapping fine particles as air passes through it. These include dust, pollen, smoke, PM2.5 and many airborne allergens. These are the particles most commonly linked to respiratory issues and poor indoor air quality. HEPA grades and what really matters You’ll often see H13 promoted as the gold standard, and it is excellent. But lower grades like H12 and even H11 can still perform extremely well, provided the purifier has high CADR. A slightly lower-grade HEPA filter moving a lot of air will outperform a higher-grade filter with weaker airflow. What matters most is: HEPA filtration (not “HEPA-like” or proprietary names) Enough airflow to cycle the room regularly Avoid vague terms like: “HEPA-style” “HEPA-type” If a manufacturer won’t clearly state the HEPA grade, it’s usually a red flag. 2. Carbon Filters: Odours, VOCs & Why Weight Matters Carbon filtration plays a different role to HEPA. While HEPA filters remove particles, activated carbon helps absorb gases and odours, such as: Cooking smells Smoke odours Chemical fumes VOCs from furniture, paints or cleaning products Not all carbon filters are equal Many air purifiers advertise carbon or VOC filtration, but include only a thin carbon-coated sheet. These filters saturate quickly and have limited ability to absorb gases. What actually makes carbon effective: Carbon pellets or granules, not just a coating More carbon weight, which increases effectiveness and lifespan A light carbon layer may slightly reduce smells, but it won’t meaningfully address ongoing odours or VOCs. Carbon filtration is optional for many homes.  If particles are the main concern, HEPA does the heavy lifting. 3. CADR: The Most Important Number on the Spec Sheet If there’s one specification to pay attention to when choosing an air purifier, it’s CADR (Clean Air Delivery Rate). CADR tells you how much clean, filtered air a purifier can deliver per hour. In simple terms, it measures how quickly a purifier can remove particles like dust, pollen and PM2.5 from a room. Higher CADR means: Faster removal of particles Better performance in larger rooms More flexibility to run at lower, quieter speeds A purifier with high CADR will always outperform a weaker one in real-world use. 4. Sizing a Purifier Properly: CADR, Room Size & Noise Most people start by thinking about the size of the room, which is exactly the right place to begin. A simple, practical rule of thumb is: Multiply your room size (m²) by 7.5 to estimate the CADR (m³/h) you need This gives you a target CADR that will deliver around 3 air changes per hour in a standard-height room. Example: 20 m² bedroom × 7.5 = 150 m³/h CADR required 65 m² living area × 7.5 = 488 m³/h CADR required This approach makes it much easier to compare purifiers objectively. Need 500+ CADR? High power, and perfect for rooms up to 65m² Key features: Runs as quiet as 16 dB on low, suitable for bedroom usage Scales up to cover living areas up to around 65 m² Reaches 51 dB at full power when maximum airflow is needed Uses true HEPA filtration for dust, pollen and PM2.5 Includes a built-in carbon filter for everyday odours No ionisers or ozone-producing technologies Shop Smart Air SA600 i. Why Manufacturer Room Size Claims Can Be Confusing You’ll often see air purifiers in NZ advertised with room size ratings that don’t line up with this rule at all. That’s because: There is no single standard for how room size is calculated Some ratings assume very low air changes per hour (even less than 1!) As a result, two purifiers both advertised for “40m² rooms" can perform very differently in practice. Looking at CADR lets you cut through this and compare models on equal footing. ii. Noise levels: What to look for in real use Noise matters because air purifiers work best when they run for long periods, not just short bursts. Living rooms, offices and daytime use In shared or daytime spaces, a bit of background noise is usually acceptable if it means better air cleaning. As a general guide: Around 50 dB is typically fine TVs, conversation and appliances often mask purifier noise Medium fan speeds often give the best balance of airflow and noise Bedrooms and overnight use In bedrooms, purifiers often run for long periods while you sleep, so lower noise becomes much more important. As a guide: Under 30 dB is ideal for overnight use Lower is better if you are noise-sensitive Avoid any with lights that may be distracting Learn More About Air Purifiers & Sleep What to be aware of for real-world quiet performance: Some brands only quote noise at the lowest fan speed That lowest speed may deliver very little CADR Quiet on paper doesn’t always mean effective in practice Important: What matters is how much CADR the purifier delivers at a quiet setting, not just the decibel number. A well-sized purifier can often deliver enough airflow for a bedroom at around 16–25 dB, allowing it to run all night without disturbance. 5. Extra features: what to be cautious of (and why) Many air purifiers include additional features that sound appealing; UV lights, ionisers, smart sensors, Wi-Fi apps and automatic modes.  Some of these can be useful in the right context, but many don’t meaningfully improve air cleaning for most homes. This doesn’t mean these features are “bad”, but it’s worth understanding what they do, and what they don’t. Common features that don't always help: Ionisers or negative ion generators UV lights Auto modes based on built in sensors App control and Wi-Fi connectivity Ionisers (negative ion/plasma modes) Ionisers (sometimes called negative ion or plasma technologies) work by electrically charging particles in the air so they clump together or settle onto nearby surfaces. This can make particle levels drop faster in CADR lab tests, but it doesn’t necessarily mean those particles are being removed from your environment. In real homes, they can end up on floors, furniture, or walls instead of being trapped in the filter. Because of this, ionisers can make performance numbers look better without improving actual filtration. Some ionising technologies can also produce small amounts of ozone as a by-product, which is why many people prefer not to introduce additional substances into their indoor air. Learn More About Ionisers Important: Some purifiers allow the ioniser to be switched off (which we'd recommend), but manufacturers rarely publish the CADR with the ioniser disabled. That makes it difficult to know the purifier’s true, filter-only performance. UV Lights UV lights are often marketed as a way to neutralise bacteria and viruses in the air. In most consumer air purifiers, however, air normally passes the UV source too quickly for meaningful disinfection to occur. It’s also worth noting that HEPA filtration already captures the vast majority of airborne particles, including dust, pollen, PM2.5, and virus-containing aerosols. For everyday indoor air quality, a well-sized HEPA purifier is already doing the most important part of the job. UV tends to add cost and complexity without improving real-world air cleaning in most homes. Auto modes and built-in sensors Automatic modes sound convenient, but how effective they are depends heavily on the quality of the sensor and where it’s located inside the purifier. Things to be aware of: Built-in sensors vary widely in accuracy Many use very low-cost sensors that can be unreliable Readings are taken at a single point, where the air is cleanest on the purifier Air quality can be poor without triggering a noticeable fan response Because of this, an auto mode may leave the purifier running slowly even when air quality isn’t ideal. Many people prefer to run purifiers at a consistent manual speed, or use a separate, dedicated air quality monitor for better insight. Wi-Fi and app control (nice to have, not essential) Wi-Fi and app control can be convenient, but they don’t make a purifier clean the air any better. They also tend to add: Extra cost More complexity Another system that can fail or become unsupported over time The need to create and manage yet another app or account For many people, this ends up being a feature that’s rarely used after the initial setup. Our purifiers don’t rely on Wi-Fi or apps, but they work well with a simple Wi-Fi smart plug if you want basic scheduling or remote on/off control, without the complexity. 6. Wrap-up: Focus on the simple features Choosing an air purifier doesn’t need to be complicated. Most of the real-world performance comes down to a few core factors, not a long list of extra features. If you focus on: Proper HEPA filtration Enough CADR for your room size Noise levels that suit how you’ll actually use it You’ll usually get better results than chasing advanced modes or add-ons that look good on a spec sheet but don’t improve day-to-day air cleaning. Simple, well-sized purifiers that move plenty of air through a good filter tend to be quieter, more predictable, and easier to live with over the long term. Looking for an air purifier that ticks all the boxes? Explore HEPA air purifiers designed for real NZ homes. Quiet enough for bedrooms, powerful enough for living spaces, and free from unnecessary gimmicks. See Product See Product Is a higher HEPA grade always better? Higher HEPA grades (like H13/H14) are most critical in settings such as hospitals, clean rooms, or labs, where air may only get a single pass through the filter. In homes, air is continuously recirculated, so airflow (CADR) and regular air changes often matter more than filter grade alone. Well-designed purifiers using H12 or even H11 filters can perform extremely well when paired with sufficient airflow. How many air changes per hour should I aim for? As a baseline, we generally recommend at least 3 air changes per hour for homes. In busier or higher-risk environments, such as schools, offices, clinics, or shared spaces, this is often increased to 4–6 air changes per hour, depending on activity levels and occupancy. Are ionisers or UV lights needed for everyday use? For most homes, no. A properly sized HEPA purifier already captures fine particles, including smoke and virus-containing aerosols. Extra technologies may sound reassuring but often add cost and complexity without improving everyday air cleaning. Should I rely on auto mode or control the purifier manually? Auto modes can be convenient, but their effectiveness depends on sensor quality and placement. In many cases, running a purifier at a consistent manual speed that delivers enough airflow for the room provides more predictable results. Relevant Articles: The Best Air Purifiers in New Zealand: 2025 Comparison Read more Ionisers Explained: Why We Don’t Use Them (and Why Some Brands Do) Read more The Misleading Room Size Claims of Air Purifier Brands Read more

Smoke can affect air quality in New Zealand at any time of year, not just during summer wildfires. Winter woodburners, controlled burns, industrial or vehicle fires, building fires, and even smoke drifting over from Australia can all push PM2.5 levels up. Events like the Port Hills Fire in Christchurch (Feb 2024) show how quickly air quality can change and how important it is to know what to do. Whether smoke is coming from your neighbour’s chimney, a nearby scrub fire, or a major incident, the aim is the same: keep PM2.5 out of your lungs and out of your home as much as possible. 1. Why Smoke Is Harmful, Understanding PM2.5 Smoke contains a mix of gases and particles, but the main concern is PM2.5: particles small enough to enter deep into the lungs and even the bloodstream. PM2.5 can: Irritate the throat, nose and eyes Worsen asthma and allergies Aggravate heart and lung conditions Cause headaches and poor sleep Build up indoors unless removed In NZ, winter woodburners regularly cause PM2.5 spikes — especially on still nights that trap smoke near the ground. Large events like the Port Hills Fire or Australian bushfire drift can cause very high short-term levels as well. If you can see or smell smoke, assume PM2.5 is elevated. 2. Keeping Smoke Out of Your Home Health NZ’s general advice during smoke events is simple: Stay indoors if possible Close all windows and doors Reduce outdoor air getting inside You can see their full guidance here → Here’s how to put that into practice at home: Close and seal your home Shut windows and doors Use curtains, door snakes, or towels to block gaps Avoid creating drafts Turn off ventilation systems that pull in outdoor air Systems such as HRV or positive-pressure ventilation often draw outside air in, and most cannot effectively filter out PM2.5. Turn these off during smoke events unless your system has a HEPA intake filter. Heat pumps are fine, they recirculate indoor air and don't draw in smoke. Reduce indoor PM2.5 contributors These activities make indoor smoke levels worse: Frying or grilling Burning candles or incense Vacuuming (which stirs up dust) Smoking indoors Keep indoor air as stable as possible. Create a Cleaner Air Space Indoors Pick a room (often a bedroom or living area) and keep the air in there as clean as possible by: Keeping windows and doors shut Reducing drafts Avoiding dust-creating activities Running a HEPA purifier This room becomes your safest indoor space during heavy smoke. 3. Checking Air Quality in NZ Smoke levels can shift quickly, whether from woodburners, fires, or drifting smoke. Checking air quality helps you know when to seal the home and when to ventilate. One challenge is that air-quality monitoring in NZ is limited.Even with community networks like PurpleAir and AirGradient, many towns and rural areas have no sensors at all. Official monitoring is even more restricted. These are the most useful tools: IQAir (best real-time map — aggregates multiple sources) IQAir combines: Official regional council monitors PurpleAir community sensors AirGradient sensors Other public/global data sources It’s often the most complete real-time view in NZ, especially if your town has no official station. View the map here → LAWA Air Quality (official NZ data + long-term trends) LAWA provides verified PM2.5 and PM10 readings where regional councils have monitors, plus: Recent hourly data Long-term and seasonal trends Annual exceedances of NZ standards Great for understanding typical patterns, coverage varies. View the map here → Indoor air-quality monitors Outdoor data doesn’t always reflect what’s happening inside your home.An indoor PM2.5 monitor helps you see: How much smoke is leaking in When levels rise How effective your purifier is This is especially useful in older NZ homes that naturally draw in outdoor air. We have a selection of Air Quality Monitors here → 4. Air Purifiers: The Most Effective Way to Reduce PM2.5 Indoors A HEPA air purifier is the most effective tool for lowering PM2.5 indoors during smoke events. Whether it’s from wildfires, woodburners, industrial fires, or long-range smoke drift. Why HEPA works best HEPA filters are extremely effective at physically trapping fine smoke particles. Their very fine weave and fibrous nature means particles big and small are captured and removed from the air. Most home ventilation systems cannot properly remove PM2.5 unless upgraded with a HEPA-grade filter, which normally isn't done as it restricts airflow significantly. What to look for HEPA filtration, H11/H12/H13 grades will be very effective High CADR / strong airflow No ionisers or plasma systems (they can create harmful byproducts) How to use your purifier During major smoke events: Run on medium–high Keep doors closed Focus on rooms you’re actively using A purifier can quickly bring PM2.5 under control even in older or draughty homes. 5. Do Carbon Filters Help? HEPA removes harmful particles. Carbon filters help with: Smoke odour VOCs from woodburners Lingering wildfire smells Fumes from industrial fires Carbon is optional for comfort, but HEPA is essential for safety. 6. Final Thoughts Smoke can impact New Zealand homes any time of year, whether from winter woodburners, wildfires, industrial incidents or far-travelled smoke. The most effective approach is: Keep smoke out Turn off systems that bring outdoor air inside Use a HEPA purifier to reduce PM2.5 Monitor air quality inside and out These simple steps help keep your indoor air healthier during smoke events. Our store contains a selection of effective and affordable air purifiers and air quality monitors designed to keep you safe from smoke.

  Ionisers in air purifiers are often marketed as a bonus feature, but they mostly boost lab test numbers rather than actually cleaning your air. Ionisers charge particles so they stick to surfaces instead of being trapped in a HEPA filter. They can artificially increase CADR scores, and turning them off usually means lower real-world performance. A test on a Blueair unit found 20–50% of CADR came from the ioniser, not the filter. Ionisers can create ozone and chemical byproducts, and increase visible dust on surfaces. HEPA-only purifiers with decent airflow are simpler, safer and more transparent. 1. The benefits ionisers claim to offer Manufacturers usually claim ionisers: “Freshen the air” “Neutralise pollutants” “Boost cleaning efficiency” “Tackle ultra-fine particles too small for filters” “Break down odours and VOCs” On paper it sounds impressive. In reality: Ionisers don’t capture particles, they just charge them so they fall onto surfaces. They don’t improve actual filtration. And the air isn’t cleaner, your surfaces just get dustier. What ionisers actually do is charge particles in the air so they stick to nearby surfaces (walls, furniture, your lungs, your skin) instead of staying airborne. 2. How ionisers inflate CADR scores without really cleaning the air This is a key reason manufacturers love ionisers. CADR tests (Clean Air Delivery Rate) measure how fast particle levels drop in a sealed test chamber. The test doesn’t care whether those particles were: Actually filtered through a HEPA filter, or Simply knocked out of the air and stuck to surfaces by the ioniser Ionisers make particles drop faster, so the CADR number gets a boost - even though the purifier hasn’t genuinely “cleaned” more air. 🚨 Important:Most purifiers let you switch off the ioniser, but when you do, the CADR is often much lower than advertised. Manufacturers almost never publish the “ioniser off” CADR, so consumers are left thinking they’re buying a higher-performing unit than they actually are. A third-party test of a Blueair purifier shows how big this gap can be. With the ioniser turned off, CADR dropped dramatically across particle sizes. Smoke fell by 44%, dust by 19%, and pollen by 53%. The researchers concluded that around 20–50% of the purifier’s measured CADR came from the ioniser, not the actual filter. Read the full report here This is why brands love ionisers: Very low manufacturing cost Bumps the test numbers Helps justify a higher price No obligation to reveal the real, filter-only performance 3. A very cheap add-on that creates a higher-priced product Ioniser modules cost very little to manufacture. Far less than a better motor, fan, or filter. But because they artificially boost test numbers, brands often use them to justify: Bigger “high-performance” claims A higher RRP Positioning the unit as “premium” or “advanced” It’s a low-cost trick with a high-margin payoff. This is one reason so many mass-market purifiers include ionisers by default: not because they’re effective, but because they sound impressive and help the spec sheet stand out. 4. The word ‘ioniser’ often goes by different names Because many people are wary of ionisers (especially due to ozone concerns), companies often rebrand them under different names, including: “Plasma ion technology” “Plasmacluster” / “PlasmaWave” “Negative ion generator” “Cold plasma” “Hypoallergenic mode” “Nanoe” “Streamer" Different name, same mechanism: charging particles so they stick to surfaces. If a purifier advertises “ionic”, “plasma”, or “active air cleaning”, always double-check what it actually does. 5. They can increase visible dust, not reduce it Because ionisers push particles out of the air and onto surfaces, you often end up with: More dust settling on furniture Black streaking on walls (common with bipolar/“plasma” units overseas) Dust build-up inside the purifier housing A proper HEPA purifier captures dust inside the filter and removes it from circulation entirely. 6. Health side: ozone, byproducts, and why NZ schools were told to avoid ionisers Ionisers can generate small amounts of ozone as a by-product. Even when the levels are low, ozone is a highly reactive gas. Indoors, it can react with everyday chemicals, things like cleaning products, perfumes, building materials and even the natural oils on skin and surfaces to create new VOCs and aldehydes. So instead of reducing chemical pollution, ionisers can unintentionally add extra byproducts to your indoor air. This is one reason many public health and education bodies advise against ionisation devices. In New Zealand, the Ministry of Education’s official ventilation guidance was very clear by requesting schools do not purchase air purifiers with ionisers for classrooms. “We recommend air cleaners with high-efficiency HEPA filters, and do not use emerging technologies that emit any substances into the air (for example ionisers, plasma discharge, ozone generators, photocatalytic oxidation or hydrogen peroxide).” That’s a strong signal that ionisers and other “active” purifier technologies aren’t yet considered safe or reliable in real-world indoor environments. 7. So why doesn’t Snap Air sell ioniser purifiers? Because they don’t fit what we stand for: No gimmicks to inflate CADR No cheap “add-on” used to justify a higher price No hidden chemistry that could add byproducts to your air All the purifiers we sell stick to transparent, well-understood tech: High airflow Proper HEPA filters Carbon filters where odours/VOCs genuinely need to be reduced No ionisers, no plasma marketing, no mystery “active” systems When you see a CADR figure on our site, it’s coming from actual filtered airflow, not ions knocking particles onto your walls. 8. What to look for instead of ionisers If you’re shopping around and want genuinely cleaner air, focus on: HEPA filter: H12 or H13 for particles CADR / airflow: big enough for your room size and target air changes per hour Carbon filter: only if you need help with smells or VOCs Noise levels: so you can actually run it at an effective speed Honest specs: no vague “plasma”, “ionic shield” or “active molecular” language You don’t need fancy-sounding tech to get clean air. You just need: A decent fan + a good HEPA filter + enough airflow for your space. If you want to skip the ioniser maze, every purifier we stock is ioniser-free and HEPA-based only, so the performance you see on the spec sheet is what you actually get in your room.