Room by Room · reference
Air Purifier for a Spare Room: What Size You Need
for a typical spare room
EPA table, 200 sq ft row · 8-ft ceiling
A spare room sizes like any bedroom: between the 100 and 200 sq ft rows, the published minimum is 130 cfm at an 8-foot ceiling.
What differs is the calendar. A spare room runs empty most of the year, which makes it the one room where round-the-clock running is habit rather than necessity, and the one place to be clear that clean air is delivered in real time. Particles return when the machine stops. That is physics, not a defect.
What the published table gives a spare room#
The row is 130 cfm for a floor between the 100 and 200 sq ft rows, smaller rows for smaller floors, larger for larger. The rounding rule travels with it: between two rows, take the larger.
Running it on a schedule#
The honest pattern is event-driven: run it before and during the days the room is used. A guest arriving tomorrow is a reason to start it today, clean air is not banked, and an empty room accrues no debt that a panic hour can repay.
The rest of the year it can rest. This is the one room where the on/off switch is a legitimate strategy rather than a shortcut.
Placement and running#
If a guest sleeps poorly and blames the machine, run it on low before they arrive and turn it down, not off. Compare small-room units with the low setting in mind.
- Plugged where it can run with the door closed, not buried behind the wardrobe it is guarding.
- Clearance on every side; spare rooms collect boxes, and boxes collect against machines.
- Check the pre-filter when a visit approaches, stored textiles shed.
What the box leaves out#
The stale smell when you first open the door is gas-phase, no published CADR exists for it, and airing the room costs nothing. The machine’s rated work is the particles, and it does that work while running, not while off.
Questions people actually ask
Sources
- U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition), retrieved 2026-08-30
Quoted and transcribed, never paraphrased into new numbers. This site does not interpolate between published figures.
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Printed from https://roomandfilter.com/rooms/air-purifier-for-a-spare-room, “Air Purifier for a Spare Room: What Size You Need”. Figures from U.S. Environmental Protection Agency, Guide to Air Cleaners in the Home (2nd edition), retrieved 2026-08-30. No prices are shown on this site, by policy.