1 Space & air changes
2 Carbon stage
Residence time = bed volume ÷ airflow. Use the value your licensing basis or specification requires.
3 Ductwork
560 Pa = IAS-NC700-HI combined HEPA + carbon clean resistance at rated flow. Fan sizing uses 2× the clean value for end-of-life filters.
Advanced: efficiencies
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What is my pressure gauge telling me?
Enter the clean reading recorded at commissioning and today's reading, taken at the same airflow. HEPA filters are changed on pressure drop. Carbon beds are not: pressure drop only flags problems, and the carbon is replaced on laboratory test results.
IAS-NC700-HI has one gauge per stage. IAS-HEPA-2424 is below 200 Pa (0.8 in. w.g.) when clean.
How the calculator works
Every number is a planning estimate from the formulas below and published IAS product data. A firm design also checks your licensing basis, contaminant, temperature, humidity and layout.
Product data used
| Item | Value | Source |
|---|---|---|
| IAS-NC700-HI airflow | 700 CFM (1,200 m³/h), 2.2 kW VFD blower, dual 300 mm (11.8 in.) collars | Product page |
| IAS-NC700-HI resistance | ≤ 560 Pa (2.25 in. w.g.) clean, HEPA + carbon at rated flow | Product page |
| IAS-NC700-HI carbon bed | 24 × 24 × 11.5 in., ≈ 0.14 s residence at 700 CFM (≈ 46 L of bed) | Comparison table |
| IAS-NC500-HI-CUSTOM | 500 CFM (849 m³/h), 24 × 24 × 16 in. bed, 0.25 s residence | Product page |
| Bulk carbon | ≈ 20 kg net per 50 L drum (≈ 0.40 kg/L) | Consumables |
| HEPA element IAS-HEPA-2424 | Clean resistance < 200 Pa (0.8 in. w.g.) | Consumables |
When to change filters, in plain terms
- HEPA: change at your site or filter maker's limit. Without one, a commonly used point is about twice the clean pressure drop or about 2 in. w.g. (≈500 Pa).
- Carbon: change when a laboratory test of a test-canister sample falls below your acceptance value (for example ASTM D3803 or your site method), or at your surveillance interval. Pressure drop does not show remaining iodine capacity.
- Carbon ΔP well above clean: look for dust loading or wet carbon; check the pre-filter and HEPA upstream and the inlet humidity.
- Carbon ΔP suddenly below clean: possible bypass, channeling or settled bed. Run an in-place leak test before trusting the stage.
Need carbon tested? Use our methyl iodide testing service or the non-radioactive cyclohexane test system. Replacement carbon, HEPA elements and adsorbers ship by part number. See also the carbon filter replacement guide and HEPA DOP/PAO testing.
Questions
At what pressure drop should a carbon bed be replaced?
There is no pressure-drop value that tells you a carbon bed is spent. Impregnated carbon loses its methyl iodide efficiency through ageing, moisture and contaminants while its pressure drop hardly changes. Carbon is replaced when a laboratory test of a test-canister sample (for example ASTM D3803 or your site's method) falls below your acceptance value, or at the interval your surveillance program sets. A pressure drop well above the clean reading points to dust or moisture; a sudden fall points to bypass or bed settling and calls for an in-place leak test.
At what pressure drop should a HEPA filter be replaced?
Use your site or filter maker's change-out limit first. Where none is set, a commonly used point is about twice the clean pressure drop, or about 2 in. w.g. (≈500 Pa). The IAS-HEPA-2424 element starts below 0.8 in. w.g. (200 Pa) when clean.
How do I calculate the airflow an air purification system needs?
CFM = room volume in cubic feet × air changes per hour ÷ 60. In metric, m³/h = room volume in m³ × air changes per hour. Add a 25% safety margin for routine work and up to 50% for high-hazard work.
How much activated carbon does an iodine adsorber need?
Bed volume = airflow × residence time. At 700 CFM and 0.25 s that is about 2.9 ft³ (83 L) of bed; at about 0.40 kg per litre that is roughly 33 kg of impregnated carbon, or two 50 L drums.
What duct diameter do I need?
Diameter = √(4 × airflow ÷ (π × velocity)). At 700 CFM (0.33 m³/s) and 10 m/s, that is about 205 mm, so a 250 mm duct; the IAS-NC700-HI has 300 mm (11.8 in.) collars.
How is fan motor power calculated?
Fan shaft power (kW) = airflow (m³/s) × total pressure (Pa) ÷ fan efficiency ÷ 1000. Divide by motor efficiency, add a service margin and choose the next standard motor size.