Common Filter Types Reference
Why this matters
Filters protect equipment + occupants. Wrong filter = damaged equipment, indoor air quality issue, OR poor performance. Customer's HVAC filter is the #1 forgotten maintenance item. The tech who teaches customers about filter sizing + schedule + matching saves equipment + gets repeat business. This is the field card.
HVAC filters (MERV rating)
MERV (Minimum Efficiency Reporting Value): 1 - 20 scale; higher = finer particles captured.
| MERV | Captures | Common Use |
|---|---|---|
| 1 - 4 | Pollen, dust mites | Construction filter, builder-grade |
| 5 - 8 | Mold spores, pet dander | Residential standard |
| 9 - 12 | Auto emissions, lead dust | Premium residential, allergy |
| 13 - 16 | Bacteria, smoke | Hospitals, surgery |
| 17 - 20 | HEPA, virus particles | Cleanrooms, biocontainment |
Residential typical:
- Basic 1" filter: MERV 6 - 8
- Pleated 1" filter: MERV 8 - 11
- High-pleated 4 - 5" filter: MERV 11 - 13
- Premium HEPA / electrostatic: MERV 13 - 16
Don't oversize MERV: too restrictive = airflow drop = equipment strain. Match equipment manufacturer spec.
HVAC filter sizes
Standard nominal sizes (actual ~ 1/4" - 1/2" smaller):
- 16x20x1 (small system)
- 20x20x1, 16x25x1, 20x25x1 (common 1")
- 16x25x4, 20x25x4 (high-pleated)
- 16x20x5, 20x20x5 (premium media filter)
Replace schedule:
- 1": every 1 - 3 months
- 4 - 5": every 6 - 12 months
- HEPA: per manufacturer
High-pet households: shorter intervals.
Air filter material
Fiberglass (cheapest): catches large dust only; ineffective for small particles; low restriction.
Pleated (paper / polyester): increased surface area; better particle capture.
Electrostatic (charged synthetic): builds static; attracts particles; washable types exist.
HEPA (true HEPA): 99.97% at 0.3 micron; not standard on residential HVAC (too restrictive).
UV light + filter: kills mold + bacteria + viruses on filter surface; supplement to filtration.
Refrigerator water filter
NSF certified: standards NSF 42 (taste/odor), 53 (lead, mercury, chlorine), 401 (pharma residuals).
Cartridge interval: 6 months OR per manufacturer.
Brands matter: aftermarket "compatible" filters may not match OEM filtration spec.
Bypass plug: if filter removed, plug installed to maintain water flow.
Pool + spa filters
Cartridge filter: pleated paper-style cartridge in housing. Easy clean (hose off); a modest cost per cartridge; replace 1 - 3 year.
Sand filter: 50 - 100 lb of #20 silica sand; backwash weekly; replace sand 5 - 7 year.
DE (diatomaceous earth) filter: finest filtration (down to 3 micron); DE powder coats grid; backwash + recharge DE; messy + expensive.
Choosing:
- Cartridge: ease + good filtration; most residential
- Sand: low maintenance + lowest cost; lower filtration quality
- DE: best clarity; highest maintenance + cost
Water softener + water treatment
Softener resin tank: media exchanges hardness ions; backwashes with brine.
Whole-house sediment filter (5 - 30 micron): pre-filter for fine particulate before softener / heater.
Activated carbon filter: removes chlorine + chloramines + organic compounds.
Reverse osmosis (RO): pre-filter + membrane + post-filter; under-sink drinking water.
Replace schedule:
- Sediment: 3 - 6 months
- Carbon: 6 - 12 months
- RO membrane: 2 - 3 years
HVAC condenser coil + evaporator coil
Outdoor condenser: dirty fins reduce heat rejection; clean with coil cleaner annually.
Indoor evaporator: dirty fins reduce heat absorption; same maintenance.
Cleaning: foam OR liquid coil cleaner spray + rinse OR brush.
Common products: NuCalgon Evap-Pow'r, Frost King coil cleaner.
Whole-house humidifier filter / pad
Evaporator pad (Aprilaire 35, Honeywell HC22): wick that water flows over; air passes through + picks up moisture.
Replace annually (mineral buildup hardens; reduces evaporation).
Common filter mistakes
Wrong size (gaps allow unfiltered air bypass). Wrong MERV (too high = airflow restriction; too low = poor filtration). Forgotten replacement (months - years overdue; severe airflow restriction; mold growth on filter). Cleaning instead of replacing (most filters can't be cleaned effectively; some can if rated washable). Reused disposable. Bypassing filter (never; even briefly = equipment damage).
Truck stock for filter work
HVAC filters (common 1" + 4" sizes), refrigerator water filter cartridges (universal + common OEM), pool cartridge (skimmer cleaner), water filter housings + sediment cartridges (5 + 25 micron), evaporator pad (humidifier).
Customer education
Most customers don't replace filters on schedule. Equipment damage from clogged filters can run into the thousands of dollars in repair, dwarfing the cost of the filter itself. Sell filter-replacement subscription OR maintenance plan with reminders. Photograph dirty filter + show customer for visual proof of need.
Common customer HVAC filter mistakes
"Filter looks gray; must be working" → gray = saturated + needs immediate replacement. "I use cheapest filter" → strain on motor + reduced airflow + dust through ducts. "Upgraded to MERV 13 for allergies" → may overload system; verify duct sizing + static pressure. "Haven't changed in 2 years" → filter collapsed; airflow restricted; equipment failing prematurely.
Filter pressure drop + sealing
Restrictive filter = blower works harder + uses more energy + airflow starvation risk. TESP increase: 0.05 - 0.30" WC depending on filter + load. Manufacturer max TESP (typical 0.5" WC residential): higher reduces airflow + performance. Filter slot gasket prevents bypass; check + add caulk OR replace gasket if dried out.
Brand cross-reference
Major HVAC filter brands: Aprilaire (4" pleated, 213 + 413), Honeywell (FC100 series), 3M Filtrete (1" + 4"), Lennox PureAir.
Refrigerator water filter: GE (XWFE, MWF), Whirlpool (Everydrop), LG (LT700P), Samsung (DA29).
Pool filter cartridge: Pleatco PLT4S25 (Pentair), Unicel C-7466 (Hayward StarClear).
Quick reference replacement intervals
| Filter | Interval | Cost |
|---|---|---|
| HVAC 1" pleated | 1 - 3 months | Lowest of the list |
| HVAC 4 - 5" media | 6 - 12 months | A few times the 1" pleated cost, but changed far less often |
| Refrigerator water | 6 months | Comparable to the 4-5" media filter |
| Pool cartridge | 1 - 3 years (or wash) | Comparable to refrigerator water filter |
| Whole-house sediment | 3 - 6 months | Among the cheapest on this list |
| Whole-house carbon | 6 - 12 months | A moderate step up from sediment |
| RO membrane | 2 - 3 years | The most expensive per-unit filter on this list |
| Humidifier pad | Annually | Similar to a whole-house carbon filter |
The single highest-value filter habit is the PHOTO-OF-DIRTY-FILTER for every service. Take a phone photo before removing the customer's old filter. Show them the difference between their filter + a new one side-by-side. Customer sees the gray-vs-white visual evidence + understands the urgency. Then offer the maintenance plan with auto-shipment OR scheduled service. Filter education + visual proof = customer commitment + recurring revenue. Most filter neglect comes from forgetting; the photo makes it real.
References
- ASHRAE 52.2 (MERV rating)
- NSF/ANSI 42, 53, 401 (water filtration)
- AHAM standards (refrigerator filters)
- Manufacturer technical data
- Manuall internal: Duct Sealing Methods, Common Pump Types