About
Air Changes per Hour (ACH) measures how often air is fully filtered. Standard rooms: 4-5 ACH. Allergies: 5-6. Wildfire smoke: 8-10. Hospitals: 12. Match purifier CADR (clean air delivery rate) ≥ room area × 0.66 for standard, 1.0 for high.
AHAM (Association of Home Appliance Manufacturers) defines CADR using an 8-foot ceiling and a 20-minute test, so the published CADR (smoke, dust, pollen) only matches reality if your room has standard height and the unit runs on its highest fan setting. Drop the fan to medium for noise and you typically lose 40-60 percent of the smoke CADR. The 2026 EPA wildfire-smoke guidance and CARB both recommend at least 4 ACH for everyday use and 6+ ACH during PM2.5 spikes, which is why HEPA H13 units rated for 350+ sq ft are now the baseline in West Coast US households.
Common pitfalls
- Buying for the "max" room size on the box: the marketing figure usually assumes 2 ACH which is rarely enough. Recompute at 5 ACH and the real coverage shrinks to about 40 percent of the box claim.
- Ignoring ceiling height: a 12-foot loft has 50 percent more volume than the AHAM 8-foot test, so you need 1.5x the CADR to hit the same ACH target.
Formula
Frequently asked questions
How accurate is the Air Purifier Sizing?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Air Purifier Sizing free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Can I use the Air Purifier Sizing on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.
Does the Air Purifier Sizing work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
How do I report a bug or suggest improvement to the Air Purifier Sizing?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.
Can I share results from the Air Purifier Sizing?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another air purifier sizing tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.
Is the Air Purifier Sizing accurate?
The Air Purifier Sizing applies the standard formula for air purifier sizing. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.
Is the Air Purifier Sizing free?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.
Are my inputs saved?
No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.
How to use the Air Purifier Sizing
The Air Purifier Sizing is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:
- Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
- Speed: results update as you type. No network round trip.
- Offline use: once the page is cached, it works without internet.
- No signup: no account, no email, no rate limits.
Step by step
- Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
- Read the result as it updates. The number reflects the formula commonly accepted in Air Purifier Sizing-related calculations.
- Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
- Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.
When you would use this
- Quick estimates: when you need a number now and don't want to open a spreadsheet.
- Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
- Comparison: running the same calculation with different inputs to compare options side by side.
- Learning: building intuition for how the underlying math behaves.
- Documentation: capturing a snapshot of inputs and outputs at a point in time.