Updated October 2026US pricing Independent
Which AirDoctor Fits Your Room — Without Overpaying
Manufacturer coverage figures are quoted at one air change per hour. Here is how to size an AirDoctor on the rate that actually matters, and which model that lands you on.
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The Rule That Makes This Easy
This one correction prevents the two most expensive mistakes: buying a small unit for a large room and wondering why nothing improved, or buying an AD5500 for a bedroom and paying $200 a year extra in filters for capacity you cannot use.
Match Your Room To A Model
| Your Space | Rough Size | Model | Why |
|---|---|---|---|
| Desk, nursery, box room | Under 150 sq ft | AD1000 / AD1500 | Single all-in-one filter, lowest cost to run, enough air changes for a small sealed room. |
| Bedroom, home office | 150–300 sq ft | AD2000 / 2000i | Three-stage filtration with carbon/VOC, and it hits a high air-change rate on a low, quieter fan speed. |
| Living room, large bedroom | 300–600 sq ft | AD3500 / 3500i | The sweet spot of the range. Separate carbon and UltraHEPA stages, sensible filter bill. |
| Large room, one cartridge preferred | 500–800 sq ft | AD4000 | Single all-in-one cartridge — one part to reorder instead of two on a split schedule. |
| Open-plan floor, kitchen-diner-lounge | 800 sq ft and up | AD5500 / 5500i | Dual filter set and the airflow to actually turn over an open floor. Expect the highest running cost. |
Sizes are at a usable 4 air changes per hour, not the manufacturer's 1 ACH headline figure.
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Four Things That Change The Answer
Ceiling height
Coverage is published for a standard 8-foot ceiling. A vaulted or 12-foot ceiling adds half again as much air volume for the same floor area, so size up a model or accept fewer air changes.
Open doorways
A 400 sq ft lounge with a wide archway into a 300 sq ft dining area is a 700 sq ft room, not a 400 sq ft one. Purifiers do not respect the floor plan on paper.
Where you actually run it
Most people settle on a medium fan speed for noise reasons, not the maximum the coverage figure assumes. If you know you will never run it on high, size up one model so medium is enough.
One big unit or two smaller ones
Two AD3500s in two rooms usually beat one AD5500 shouting through a doorway, and often cost about the same to buy. Air does not move between rooms quickly enough for a single unit to serve both well. The exception is a genuinely open floor with no walls, which is exactly what the AD5500 is built for.
Know Which Model You Need?
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Frequently Asked Questions
What size air purifier do I need for my room?
Measure the floor area, then pick a unit whose manufacturer coverage figure is at least four times that number. Manufacturers publish coverage at 1 air change per hour; you want 4 to 5 air changes per hour for allergens, pet dander and smoke, so dividing the headline figure by four gives the realistic room size.
Which AirDoctor is best for a bedroom?
The AD2000. At bedroom square footage it reaches a high air-change rate on a low fan speed, which keeps it quiet at night, and it has the lowest filter cost in the range at roughly $120 to $140 a year.
Is one AD5500 better than two AD3500s?
Only in a genuinely open-plan space with no walls between the areas. If there are doorways, two AD3500s will deliver more useful air changes in both rooms, usually for a similar purchase price — though you then pay two filter bills instead of one.
Does ceiling height affect which model I need?
Yes. Coverage figures assume a standard 8-foot ceiling. A 12-foot or vaulted ceiling adds roughly 50% more air volume for the same floor area, so either size up a model or accept proportionally fewer air changes per hour.