Community Air Purifier Deployment and Filter Replacement Calculator
How this community air purifier planner works
This calculator helps you plan portable HEPA air purifier deployment and filter replacement for community spaces such as classrooms, community centers, faith spaces, shelters, and event venues. By entering a target clean air delivery rate (CADR) per room, the CADR of your chosen purifier model, filter life, runtime, and budget, you can estimate how many units you need, how often you will replace filters, and whether your planned program fits your annual supplies budget.
Key concepts: CADR, ACH, and runtime
Clean Air Delivery Rate (CADR) measures how much clean air a purifier delivers, typically in cubic feet per minute (cfm). Higher CADR means faster removal of particles like dust, smoke, and aerosols.
Air changes per hour (ACH) describes how many times per hour the air in a room is replaced with clean or filtered air. Community health guidance often recommends higher equivalent ACH for infection control than for basic comfort.
Your target CADR per room is usually derived from the room volume and desired ACH. A simplified relationship is:
where room volume is in cubic feet, ACH is air changes per hour, and CADR is in cfm. This tool assumes you already have a target CADR per room and focuses on translating that target into purifier units and filter budgets.
Average daily runtime is how many hours per day the purifiers will be on. Longer runtimes deliver more clean air but also use up filter life faster.
Formulas used in the calculator
Once you enter your inputs, the calculator uses straightforward planning formulas:
- Units needed per room = Target CADR per room ÷ CADR of selected purifier (rounded up to the nearest whole purifier).
- Total units for all rooms = Units per room × Number of rooms or zones.
- Daily filter use (hours) = Average daily runtime.
- Filter life in days = Filter service life (hours) ÷ Average daily runtime.
- Filter life in years = Filter service life (hours) ÷ (Average daily runtime × 365).
- Filter replacements per unit per year ≈ 1 ÷ Filter life in years.
- Annual filters needed = Total units × Filter replacements per unit per year.
- Annual filter spend = Annual filters needed × Replacement filter cost.
The calculator then compares the estimated annual filter spend to your annual clean air supplies budget so you can see whether your plan is under, at, or above budget.
Interpreting the results
After running a calculation, you will typically see:
- Units required per room or zone so you can confirm that each space meets your target CADR.
- Total purifiers needed across all rooms, helpful for procurement and deployment planning.
- Estimated filter replacement interval (e.g., every X months), based on runtime and rated filter life.
- Projected annual filter cost, based on the number of units and how often filters are replaced.
- Budget alignment, indicating whether your projected annual spend is below, near, or above your stated budget.
If your projected annual cost exceeds your budget, you can adjust:
- Target CADR (if local guidance allows a lower target while still maintaining reasonable protection).
- Purifier CADR (e.g., selecting a different model with a different CADR/price balance).
- Average runtime (e.g., running on high during highest risk periods and lower the rest of the time).
- Budget amount (if the plan shows that more funding is realistically needed to maintain clean air goals).
Worked example: small community learning center
Imagine a learning center with 4 classrooms. Each classroom is similar in size and use. The program wants to reach a target of 260 cfm per room using portable HEPA purifiers. They are considering a unit with a CADR of 200 cfm, a rated filter life of 3,000 hours, and replacement filters that cost $85 each. Purifiers will run 12 hours per day during active periods. The annual supplies budget is $2,500.
Inputs:
- Rooms or zones to cover: 4
- Target CADR per room (cfm): 260
- CADR of selected purifier (cfm): 200
- Filter service life (hours): 3,000
- Average daily runtime (hours): 12
- Replacement filter cost ($): 85
- Annual clean air supplies budget ($): 2,500
Step 1: Units per room
Units per room = 260 ÷ 200 = 1.3, which rounds up to 2 purifiers per room to meet the target CADR.
Step 2: Total units
Total units = 2 per room × 4 rooms = 8 purifiers.
Step 3: Filter life in years
Daily runtime = 12 hours, so annual runtime per unit = 12 × 365 = 4,380 hours. Filter life in years = 3,000 ÷ 4,380 ≈ 0.685 years, or about 8.2 months.
Step 4: Filters per unit per year
Filters per unit per year ≈ 1 ÷ 0.685 ≈ 1.46 filters. You might round this to 1.5 filters per unit per year for planning.
Step 5: Annual filters and cost
Annual filters ≈ 8 units × 1.46 ≈ 11.7 filters; in practice, you may plan for 12 filters. Annual filter spend ≈ 12 × $85 = $1,020.
Step 6: Compare to budget
With a budget of $2,500, the estimated annual spend of about $1,020 is within budget, leaving room for extra filters, pre-filters, or additional units if needs grow.
Comparison of example scenarios
The table below shows how different community spaces with the same purifier model can lead to different purifier counts and budgets. These are illustrative scenarios using similar assumptions (12-hour runtime, 3,000-hour filter life, $85 filters).
| Scenario | Rooms / zones | Target CADR per room (cfm) | Unit CADR (cfm) | Purifiers needed | Approx. filter changes per unit per year | Estimated annual filter cost |
|---|---|---|---|---|---|---|
| Small learning center | 4 classrooms | 260 | 200 | 8 | ~1.5 | ≈ $1,020 |
| Mid-size community hall | 2 large halls | 400 | 250 | 4 | ~1.5 | ≈ $510 |
| Multi-room faith community | 8 rooms | 220 | 200 | 9 | ~1.5 | ≈ $1,150 |
Use similar comparisons to see how changing the target CADR, purifier model, or number of rooms affects your annual supplies plan.
Using the results for budgeting and program planning
Community organizations can use this calculator in several ways:
- Annual budget planning: Estimate how much to allocate for filters over a fiscal year, and include a margin for unexpected extended runtimes or special events.
- Bulk purchasing: Determine how many filters to buy at once to secure volume discounts while avoiding excessive inventory that may age on shelves.
- Deployment strategy: Decide whether to concentrate more units in the highest-risk spaces (e.g., crowded classrooms, waiting areas) while keeping lower CADR targets in lightly used rooms.
- Funding proposals: Share clear estimates of units and ongoing filter costs with funders, boards, or mutual aid partners to justify grants or donations.
Assumptions and limitations
This calculator is a planning aid, not an engineering design tool. It relies on several simplifying assumptions:
- Uniform room size and use: All rooms are treated as if they have similar volume and use patterns, using a single target CADR per room.
- Manufacturer-rated CADR and filter life: CADR and service life are taken at face value from product documentation and assumed to be constant over time.
- Linear filter wear: Filter life is assumed to decrease proportionally with runtime; variations in pollutant load, humidity, and user maintenance are not modeled.
- Constant runtime: The average daily runtime is treated as the same every day of the year, without seasonal or occupancy-based adjustments.
- No building ventilation modeling: Existing HVAC systems, open windows, and infiltration are not included; the focus is portable HEPA units only.
- Well-mixed air assumption: The calculator assumes that air in each room is reasonably well mixed so that CADR can be applied at the room scale.
- Costs limited to filters: Only replacement filter costs are considered; electricity, maintenance labor, and unit replacement are excluded.
Because of these limitations, you should treat the outputs as order-of-magnitude planning estimates. For critical environments (e.g., healthcare spaces or highly crowded shelters), consult with building engineers or indoor air quality specialists and follow local public health guidance when setting CADR and ACH targets.
Why a Community Air Purifier Planner Matters
Many neighborhoods have stepped up mutual aid responses to wildfire smoke, construction dust, and lingering airborne pathogens by setting up clean air rooms in libraries, community centers, and faith halls. The challenge is that guidance from government agencies often assumes commercial budgets or proprietary equipment, while grassroots teams work with donated purifiers, volunteer maintenance, and shoestring supply funds. This calculator helps bridge that gap by translating indoor air quality targets into a concrete deployment and replacement plan. Instead of guessing how many HEPA units to borrow or how often to swap filters, coordinators can plug in room counts, target clean air delivery rates (CADR), runtime expectations, and filter costs to reveal actionable numbers.
By mirroring the familiar interface of tools like the neighborhood cooling center capacity and supply planner and the community fridge restocking and spoilage planner, this calculator stays consistent with the broader resource hub. Volunteers navigating disaster response rarely have time to learn new software, so the fields here map directly to data they already track: number of rooms, target CADR, the purifier model’s rated airflow, filter service hours, runtime, and supply budgets. The result is a deployment plan backed by transparent math.
How the Calculations Work
The core of the tool is the relationship between the target clean air delivery rate and the purifier’s rated CADR. If a room needs a CADR of 260 cubic feet per minute and the available purifier delivers 200 cfm, you need more than one unit to meet the target. The calculator divides the target CADR by the unit’s CADR, rounds up to the next whole number, and multiplies by the number of rooms. That yields a fleet count. It then estimates how many hours each purifier will run per year based on daily runtime. Because filter service life is usually reported as hours of operation, the tool divides the annual runtime by the filter life to determine how many filter changes are required for each purifier.
The math is captured by the following expression:
where is the number of purifiers required, is the room count, is the target CADR per room, and is the purifier CADR. Because CADR requirements are rarely perfect multiples of unit capacity, the ceiling function ensures you plan for enough purifiers rather than leaving a room under-served.
After establishing the fleet, the script calculates runtime-based filter burn. The annual runtime for each device equals daily runtime times 365. Dividing that by the filter service life yields the number of filters needed per year per device. The tool multiplies by the filter cost and the fleet size to arrive at the annual supply expenditure. It also compares the total with your stated budget, flagging whether your plan is under, over, or exactly at the spending limit. Finally, it estimates the number of days between filter changes by dividing the filter life hours by the daily runtime, providing a practical cadence for volunteers.
Worked Example
Imagine a community center preparing four rooms for wildfire smoke season. Each room is about 500 square feet, and volunteers aim for a CADR of 260 cfm to deliver five air changes per hour. The center has access to portable units rated at 200 cfm. Filters last 3,000 hours and cost $85 apiece. The team plans to run the purifiers 12 hours per day during active smoke weeks but expects to keep them on a lighter schedule off-season, averaging out to that same daily runtime. Their annual supply budget is $2,500.
Plugging these values into the calculator reveals they need 8 purifiers total: two per room to reach the CADR goal. Each purifier operates for 4,380 hours per year (12 hours × 365 days), so each will consume 1.46 filters annually. Rounding up for practical stocking means budgeting two filters per purifier per year, totaling 16 filters. At $85 each, that is $1,360—comfortably below the $2,500 budget. The filter change interval is roughly every 250 days, or about every eight months, suggesting a twice-per-year schedule will stay ahead of performance degradation. The results also show that the budget can cover up to 29 filters, leaving room for emergency stockpiles or upgrading to activated carbon prefilters.
Scenario Comparison Table
To help with planning conversations, the table below compares three scenarios for different room counts and runtime assumptions using the same purifier model and filter cost.
| Scenario | Rooms Covered | Daily Runtime | Purifiers Needed | Annual Filter Cost |
|---|---|---|---|---|
| Baseline | 4 | 12 hours | 8 | $1,360 |
| Expanded Smoke Shelter | 6 | 16 hours | 12 | $2,720 |
| Pop-Up Classroom Rotation | 3 | 8 hours | 6 | $816 |
These comparisons illustrate how runtime is a major driver of filter expenses. Extending daily operation from 12 to 16 hours nearly doubles costs because filters accumulate wear in proportion to hours run. Conversely, scaling down to three rooms with shorter runtime cuts expenses almost in half. Coordinators can use this view to decide whether to rotate purifiers between rooms, limit operation to peak smoke periods, or invest in higher-capacity units that reduce fleet size.
Linking with Other Planning Tools
Clean air interventions intersect with many other community resilience strategies. Budget insights from the resilience hub backup power coverage calculator help determine whether battery backups can keep purifiers running during outages. The cooling center planner already tracks seating, hydration, and staffing needs; pairing it with this tool ensures the same space also delivers breathable air. For donation drives, results from the mutual aid fund runway calculator can show if recurring contributions can sustain filter purchases over the long term.
Limitations and Assumptions
The calculator assumes uniform rooms and ignores differences in ceiling height, leakage, and infiltration rates. It also assumes filters are replaced proactively rather than waiting for sensors to indicate clogging. In reality, wildfire smoke events can overload filters quickly, while off-season operation may stretch intervals. The tool does not model multi-stage systems, activated carbon add-ons, or ionization devices with different maintenance requirements. CADR ratings listed by manufacturers are often measured in controlled labs and may not reflect real-world reductions due to furniture placement or poor filter sealing. Finally, budgets entered here consider only filter costs; replacement prefilters, fan maintenance, electricity, and volunteer labor are not automatically included and should be tracked separately.
Practical Tips for Using the Results
Treat the output as a starting point for discussions with building managers, health advocates, and volunteer crews. If the budget gap is small, consider fundraising campaigns timed with the most intense smoke season, using the calculated filter count as a tangible ask. When the number of purifiers required feels daunting, explore borrowing units from neighboring institutions or staggering deployment so that high-priority rooms are covered first. The filter change interval can be turned into a maintenance calendar, aligning with volunteer schedules or events like mask distribution days. Document decisions in shared notes so everyone knows which rooms are being served, how many backup filters are stored, and when replacements were last performed.
Clean indoor air is increasingly recognized as a collective responsibility. By putting concrete numbers to purifier counts, filter schedules, and budget needs, this calculator gives mutual aid groups the clarity they need to protect neighbors, elders, and immunocompromised residents when outdoor air is hazardous.