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 pleated / electrostatic: MERV 13 - 16. True HEPA sits above this range and does not belong in residential ductwork; anything sold as "HEPA" at MERV 13 is not HEPA
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: NSF 42 covers aesthetic effects (taste, odor, chlorine), NSF 53 covers health effects (lead, cysts, VOCs), NSF 401 covers emerging contaminants such as pharmaceutical residuals. A filter certified only to 42 has said nothing about lead.
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: #20 silica sand, quantity by tank size (roughly 100 lb in a small 16 inch tank up to 300 lb or more in a 24 inch); 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. A clogged filter that starves airflow long enough takes out a blower motor or a compressor, and either of those dwarfs a lifetime of filters. 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