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Find Your Air Purifier in 60 Seconds

In brief: Which air purifier should i buy? Answer 6 quick questions about your room, pets, allergies and budget to get matched with the right air purifier.

Which Air Purifier Should I Buy

What the calculator does (and what you’ll need)

This tool converts a room’s dimensions and your cleanliness goal into a single target: the minimum CADR (clean air delivery rate, in CFM) a purifier should deliver to meet that goal. The math runs server-side so editors can show the exact steps and a worked example without relying on browser scripts.

Tool inputs and the immediate output you should expect

  • Room dimensions: length, width, height in feet. Quick presets for common rooms and a one-click toggle that assumes an 8 ft ceiling if you only enter length × width.
  • Goal selector (preset ACH): General — 2 ACH; Allergy/Respiratory Concern — 4 ACH; Smoke/High Particle Load — 6 ACH. These are defaults you can override.
  • Extra modifiers (checkboxes): Pets (+25%), Heavy cooking or smoking (+50%), Open-plan (+25%). These are applied multiplicatively to the base CADR after the initial calculation; the UI shows the percent adjustments explicitly.
  • Server-rendered output panel shows: computed room volume (ft³), chosen ACH, required CADR (CFM) rounded to the nearest 5 CFM, and a one-line interpretation (for example, “This equals a small–medium purifier; aim for CADR ≥ 120 CFM”).
  • Result-based picks: a single-row “Recommended models” CTA with three curated links (compact, mid-range, premium) that take you to the site’s buying pages. Affiliate disclosure appears beneath the picks.

Canonical formula and how it appears on the page

Show this verbatim so the calculation is unambiguous:

CADR (cfm) = (room length × width × height in feet) × target ACH ÷ 60.

Brief unit note: length × width × height gives volume in cubic feet (ft³). Multiplying by ACH gives cubic feet per hour; dividing by 60 converts to cubic feet per minute (CFM), the same units manufacturers use for CADR. After computing the base CADR, apply modifiers as multipliers. For example:

Final CADR = Base CADR × (1 + pet_modifier + heavy_modifier + …) × open_plan_multiplier.

Rounding rule: round the required CADR to the nearest 5 CFM for readability, and when comparing with manufacturer CADR values choose the next higher listed CADR if the spec is split by particle type.

Worked example (no JavaScript needed)

  1. Scenario: 12 ft × 15 ft room, 8 ft ceiling → volume = 12 × 15 × 8 = 1,440 ft³.
  2. Target: Allergy setting (4 ACH).
  3. Base CADR = (1,440 × 4) ÷ 60 = 96 CFM (round to 95 or 100 CFM; we use nearest 5 → 95 CFM).
  4. Apply pet modifier (+25%): final CADR = 96 × 1.25 = 120 CFM. Display: “Result: choose models with CADR ≥ 120 CFM.”
  5. If the room is open-plan too, multiply again by 1.25: 120 × 1.25 = 150 CFM; choose models at or above 150 CFM.

From CADR to product picks (practical guidance)

CADR bands are heuristics, not rules, but useful for shopping:

  • <150 CFM — typically suitable for small bedrooms and offices.
  • 150–300 CFM — common living rooms and medium spaces.
  • >300 CFM — large rooms, open-plan areas, or multi-room coverage.

Result-based picks: the tool will show three linked options (compact, mid-range, premium) that match your CADR target and link to our buying guide at /best/. Shop recommended models — affiliate links; selected to match your CADR target. Disclosure: AirPurifierFAQ earns a commission if you buy through these links; this does not change our editorial selection.

If no single model matches your target, choose the next higher CADR or use two smaller units placed apart for better circulation; the tool explains when a multi-unit setup is preferable.

Important edge cases and adjustments

  • Open-plan or connected spaces: increase required CADR by ~25% or run multiple units to avoid a single unit being overwhelmed.
  • Multiple occupants/frequent visitors: increase ACH one level (e.g., from 2 → 4) to maintain air turnover.
  • Wildfire or heavy smoke: use the highest ACH preset and compare your target to the manufacturer’s smoke CADR, if provided.
  • Bedroom overnight use: calculate for the bedroom only and prioritize low-noise models; you may accept a slightly lower fan speed at night.
  • Older homes with drafts: infiltration reduces effectiveness—consider a modest CADR increase and consult our ACH calculator for sealing-sensitive estimates.

Filter types, maintenance and running cost

  • HEPA filters: “true HEPA” is the standard term for high-efficiency particulate filtration—read product pages for exact filter specifications rather than assuming uniform performance.
  • Prefilters extend main-filter life; activated carbon layers reduce many odors and some gases but are not a complete solution for all VOCs.
  • Factor in replacement cadence: heavy use, pets, and smoke shorten filter life. Use our filter reminder tool and the running cost calculator to estimate ongoing expenses.

Noise, placement and setup tips

  • Placement: ideally central in the room, away from walls and furniture by 2–3 ft; avoid blocking intakes or exhausts.
  • Noise vs. CADR: higher fan speeds raise CADR but also noise—run high speed during high-particle events and lower it for overnight comfort.
  • Multiple units: two medium units placed apart often circulate air better than one very large unit tucked in a corner.
  • Check warranty and return policy before buying; models with flexible returns are safer if you’re unsure about coverage.

How it works — plain language

CADR is a measure of how much filtered air a purifier delivers per minute; higher CADR cleans faster. ACH is how many times per hour the unit filters the entire room volume. The calculator converts your target ACH into the CADR value manufacturers use, which is why the formula multiplies room volume by ACH and divides by 60.

FAQ (short answers)

Do I need the same CADR for pollen, dust and smoke?

Manufacturers sometimes list separate CADR numbers for smoke, pollen and dust. For smoke-heavy situations use the smoke CADR; for allergies look at pollen/dust CADR. When in doubt, compare the highest-reported CADR relevant to your concern.

Can I use one purifier for my whole apartment?

Only if one room’s volume essentially equals the living area and the unit’s CADR meets that volume’s requirement. In most apartments, multiple units or a higher-CADR unit in an open-plan space are better.

How much should I increase CADR for pets or smoke?

Use the tool’s suggested modifiers: pets +25%, heavy cooking/smoking +50%. These are practical adjustments, not precise scientific corrections.

Where can I compare models that match my CADR?

See our buying guide at /best/ or use the site’s comparison tools under /tools/.

Sources for “Which Air Purifier Should I Buy”

To keep our answer to “Which Air Purifier Should I Buy” accurate, we rely on independent references such as the EPA’s Guide to Air Cleaners in the Home, AHAM Verifide CADR data and manufacturer spec sheets. See how we evaluate air purifiers and our editorial policy for details.

FAQ

Questions buyers often ask

If my room has a nonstandard ceiling height, what should I enter in the tool?

Enter the actual room height (feet) into the height field. The one-click toggle only assumes an 8 ft ceiling when you supply length × width only. The calculator uses the full volume (length × width × height) in its CADR formula, so providing the correct height gives a more accurate target.

Do the extra modifiers (pets, heavy cooking/smoking, open-plan) stack, and how are they applied?

Yes — modifiers are applied multiplicatively after the base CADR is computed. The tool multiplies the base CADR by (1 + pet_modifier + heavy_modifier + …) and then by the open-plan multiplier. The UI shows each percent adjustment and the final multiplied CADR so you can see how the total increases.

A purifier lists separate CADR values for smoke, dust and pollen — which one should I use to compare to my target?

Compare your target to the CADR that matches the particle type of concern (e.g., use smoke CADR for wildfire/smoke events, pollen for allergy settings). If the spec is split, follow the page guidance: choose the next higher listed CADR than your calculated requirement to ensure adequate coverage.

Should I buy one large unit or two smaller units for an open-plan area?

The tool suggests either choosing a single unit with CADR at or above your target or deploying two smaller units placed apart for better circulation. If no single model matches, consider multiple units. Verify that the combined setup meets or exceeds your target CADR and place units apart for improved airflow; the tool explains when multi-unit setups are preferable.

How should I balance CADR and noise for bedroom overnight use?

Calculate CADR for the bedroom only and prioritize models listed as low-noise on their product pages. The page advises running higher fan speeds during high-particle events and lowering speed overnight. You may accept somewhat lower fan speed at night, but ensure the reduced speed still provides acceptable filtration relative to your ACH/CADR target.

My home is drafty—how much should I increase the required CADR?

The page notes infiltration reduces purifier effectiveness and recommends a modest CADR increase, but it doesn't give a specific percentage. Verify how drafty the space is and consider increasing your CADR target or consulting the site’s ACH calculator for sealing-sensitive estimates before choosing a model.

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