Portable Air Cleaner Smoke Event Runtime Planner

Introduction

Wildfire smoke is no longer a seasonal inconvenience confined to a few fire-prone regions. In recent years, people far from the flames have spent days or even weeks indoors while fine particulate matter drifts across states and provinces. Portable HEPA air cleaners are one of the fastest ways to make a single room safer, but the label on the box rarely answers the practical questions people actually face during a smoke event. A package may list a Clean Air Delivery Rate, a fan speed, and a broad room-size recommendation, yet that snapshot does not tell you whether your purifier can protect a bedroom with a tall ceiling, a living room with an open doorway, or a home office where you need lower noise overnight.

This runtime planner closes that gap by translating smoke CADR into air changes per hour, then comparing that cleaning rate with the room volume and the number of smoky hours you expect each day. Instead of guessing whether to run the machine continuously, only at peak smoke, or only on the highest setting, you can estimate how much runtime each fan speed would need to hit your target. The page also turns those operating choices into costs that are easier to understand in everyday terms: electricity use per day, filter replacement timing, and filter wear cost per day.

That matters because smoke planning is rarely about just one variable. A purifier that is quiet enough for sleep may not move enough clean air to maintain a high ACH target in a larger room. A high-speed mode may clear smoke rapidly, but it can be louder, use more electricity, and shorten the time until the next filter change. This calculator is designed to show those tradeoffs clearly. If one speed comfortably meets your goal, the summary highlights it. If none of the speeds can keep up, the planner shows the shortfall so you know whether to shrink the protected space, seal leaks more aggressively, or add another purifier.

How to use this runtime planner

Start by describing the room you want to protect. Choose feet or meters, then enter the room length, width, and ceiling height. Because CADR ratings for portable air cleaners are usually expressed in cubic feet per minute, the tool converts metric dimensions automatically before doing the ACH calculation. Next, enter the number of hours per day when heavy smoke is likely to affect the room. This field is useful because many households do not need full-day operation year-round; instead, they may need the purifier during the evening, overnight, or only during the most intense part of a smoke episode.

After that, set your target air changes per hour and fill in the operating-cost fields. Target ACH is the level of air cleaning you are trying to maintain in the room, with five ACH often treated as a practical baseline for smoke response and higher targets used when smoke is severe or occupants are especially sensitive. Filter life in hours, filter replacement cost, and electricity price turn a technical airflow question into an operating plan that is easier to budget. Finally, enter up to three fan speed profiles. For each one, use the smoke CADR if you have it, because smoke CADR is often lower than the dust or pollen number shown in marketing materials.

1. Enter the room size and smoke exposure window.
2. Choose your target ACH and cost assumptions.
3. Fill in one to three purifier speed profiles with smoke CADR and wattage.
4. Click Plan runtime to compare runtime, energy use, filter timing, and any ACH shortfall.

When the results appear, read the top summary first. If a speed can meet the target, the tool points to the lowest combined day-to-day cost among the speeds that qualify. Then scan the table to see the full tradeoff. Runtime needed shows how long that speed would need to run during the smoky part of the day. kWh per day and energy cost per day reflect the electrical cost of that runtime. Days until filter change tells you how quickly heavy seasonal use could consume a filter. If a row shows an ACH shortfall, that speed cannot fully maintain your target even if it runs for the entire smoke window.

How CADR becomes ACH, runtime, and filter wear

CADR expresses how many cubic feet of clean air a purifier delivers per minute. To convert that to air changes per hour, you multiply by 60 and divide by the room volume $V$. In MathML:

Formula: ACH = (CADR ⁢ 60) / V

$\mathrm{ACH}=\frac{\mathrm{CADR}60}{V}$

When you set a target ACH $A_t$ and the purifier can only run for part of the day, the required runtime fraction $F$ is $F=\frac{A_t}{\mathrm{ACH}}$. If $F$ is less than or equal to 1, running the purifier for $F$ times the daily exposure window will meet the target. If $F$ exceeds 1, the purifier must run the entire exposure window and still falls short by $A_t-ACH$.

Energy consumption follows from the power draw $P$ in watts. Dividing by 1,000 converts watts to kilowatts, and multiplying by runtime gives daily kWh. Filter life in days is the rated filter life in hours divided by the daily runtime, while filter cost per day is the replacement cost divided by that projected day count. Put together, these relationships reveal an important planning truth: the fastest speed is not always the cheapest way to reach your target, and the quietest speed is not always strong enough to keep the room under control during a bad smoke episode.

Input choices and validation

The room dimension fields accept decimals so you can represent irregular spaces, partial-room zones, or metric conversions without rounding too early. Ceiling height defaults to eight feet because that is common in many homes, but even a modest increase in height can noticeably reduce ACH because the purifier has more volume to clean. The exposure duration field captures how many hours per day you expect meaningful smoke intrusion. In some homes that may be a 12-hour overnight window; in others, especially during prolonged regional smoke events, the realistic answer is closer to 24 hours.

Filter-life and filter-cost inputs are there to make the result useful after the headline airflow calculation. Manufacturers often quote filter replacement intervals in months, but those intervals assume moderate use. During wildfire season, a unit that runs long hours every day can use up a filter much faster than the box suggests. For the speed profiles, you can enter one, two, or three rows. The planner automatically ignores any speed with a CADR of zero. Noise data is optional, but it helps when you want to compare whether a slightly slower, quieter speed is still acceptable for a bedroom, nursery, or shared work space.

Worked example: Preparing a living room for a week of wildfire smoke

Imagine a family in Portland with a 16-by-18-foot living room and a nine-foot ceiling. They expect to shelter indoors for 14 smoky hours per day and want at least six ACH. Their purifier offers three speeds: low at 150 CADR and 45 watts, medium at 250 CADR and 75 watts, and high at 400 CADR and 130 watts. When those figures are entered, low speed delivers only about 3.1 ACH. To reach six ACH, the runtime fraction would be 1.94, which means even constant operation during the whole 14-hour smoke window would still leave the room below target.

Medium speed performs much better, reaching about 5.2 ACH. That is close, but still not enough to hold a six-ACH goal without nearly continuous operation, and it may still show a shortfall depending on the exact room volume. High speed, however, delivers roughly 8.3 ACH, so it needs only about 10.1 hours of runtime during the 14-hour smoke period to satisfy the target. The planner then shows the secondary consequences of that choice: higher kWh per day, higher daily electricity cost, and fewer days until the filter reaches its rated life. This is exactly the kind of tradeoff that is difficult to see from a product box but easy to compare once all speeds are shown in the same table.

Comparison of common purifier sizes in a 200 square-foot room

It can also help to step back and compare rough purifier classes before looking at a specific model. In a 200-square-foot room with an eight-foot ceiling, a small purifier may be helpful but still undersized for strong smoke control, while a medium-to-large unit may create a comfortable margin that lets you use shorter runtime or quieter settings. The comparison below illustrates how different smoke CADR levels translate into practical runtime needs.

Notice that the larger unit is not simply about speed for its own sake. More CADR means a higher possible ACH, which gives you flexibility. You can hit the same target with fewer hours of operation, preserve a cushion when smoke worsens, or potentially drop to a quieter setting for part of the day while still staying on plan. That is why many smoke-season buyers think in terms of room volume and target ACH rather than the square-footage sticker alone.

Assumptions and limitations

This planner models one room and assumes the portable cleaner is the main filtration device for that space. Real homes are messier. Smoke can leak in through doors, windows, and bathroom fans. A central HVAC system may add filtration if it is equipped with an appropriate filter, or it may move air between rooms in ways that change the effective particle load. The calculator also treats the purifier's CADR as stable, even though heavily loaded filters usually perform worse over time. For that reason, the output should be read as a planning estimate rather than a guarantee of exact indoor particle concentration.

The tool also assumes that filter life scales roughly with operating time. That is a practical assumption for budgeting, but it is still a simplification. Dense smoke can clog a filter faster than light routine use, and many purifiers include multiple filter stages whose replacement schedules are not identical. If your device has a washable pre-filter, activated carbon layer, and HEPA filter, check the manufacturer's maintenance instructions and use this calculator as a way to estimate relative wear rather than a strict service deadline. The best real-world strategy is to pair the runtime plan with common-sense smoke controls: keep windows closed when outdoor air is poor, reduce indoor combustion, monitor local air quality reports, and if possible verify your indoor conditions with a PM2.5 sensor.