Furnace Filter Size Guide for Portland Homes (2026)
Correct filter sizing protects your furnace, keeps indoor air clean, and ensures Portland’s wildfire smoke stays out of your living room. Use this step-by-step guide to measure, select, and replace filters with confidence.
Read Time
8 minute read
Service Area
Portland Metro
License
CCB #187834
Owner & Lead HVAC Technician
Quick Answer
Measure your current filter slot (length x width x thickness). Common Portland sizes: 16x25x1, 20x25x1, 14x25x1. Use MERV 11-13 for pollen and wildfire smoke. Replace every 30-90 days, more often during high pollen season. Check furnace manual or label for exact size to avoid airflow issues.
| Filter Size | Typical Homes | Portland Notes | Replacement Frequency |
|---|---|---|---|
| 16x25x1 | Craftsman bungalows, ranch homes, townhomes | Most common Portland size; fits standard return grilles. | Every 60 days |
| 20x20x1 | Split-levels and mid-century homes | Often paired with wall returns in SE Portland and Gresham. | Every 45 days |
| 20x25x1 | Newer construction (Bethany, Happy Valley) | Supports higher airflow for multi-story homes. | Every 45 days |
| 16x20x1 | Condominiums & smaller furnaces | Verify airflow with higher MERV filters to avoid static pressure issues. | Every 30-45 days |
| 16x25x4 / 20x25x4 | Homes with media filter cabinets | Popular in premium installations; lasts 6–12 months. | Every 6 months |
Why Filter Sizing Matters in Portland
The wrong filter size compromises airflow, forces your blower motor to work harder, and lets smoke, pollen, and dust recirculate. Over time that leads to higher energy bills, icy coils, dirty ducts, and shortened furnace lifespan.
Correct sizing paired with the right MERV rating keeps Portland’s wildfire smoke out, reduces asthma triggers, and preserves warranties. Efficiency Heating & Cooling audits filter sizing on every maintenance visit to ensure your system performs like it should.
Portland’s diverse housing stock—Craftsman, mid-century, modern infill—means filter sizes vary widely. Measure to be sure.
Media filter cabinets improve filtration and reduce replacement frequency. Upgrade during furnace replacements.
Proper filter sizing keeps blower static pressure within manufacturer limits, protecting ECM motors.
How to Measure Your Furnace Filter
Grab a tape measure and follow these five steps. They work for return grille filters, cabinet filters, and filter racks inside the furnace.
1. Turn Off HVAC System
Shut off the furnace or turn the thermostat to OFF. Removing filters while the system runs can pull dust into the blower chamber and ductwork.
2. Remove Current Filter Carefully
Slide the existing filter out of the return grille or filter cabinet. Note the airflow arrow direction—pointing toward the furnace.
3. Check Printed Dimensions
Most filters list nominal size on the frame (e.g., 16x25x1). If blank or illegible, proceed to measure manually.
4. Measure Filter Slot (Actual Size)
Use a tape measure to record width, height, and depth of the slot/cabinet in inches. Round down to the nearest standard size. A 15.5"x24.5"x0.75" slot corresponds to a 16x25x1 filter.
5. Label the Cabinet
Write the correct size on the filter housing with a permanent marker or label. Future replacements become effortless—especially for tenants or family members.
Common Furnace Filter Sizes in Portland Homes
Here are the sizes we encounter most often across the metro. Still measure to confirm—builders sometimes mix sizes within the same neighborhood.
| Nominal Size | Common Portland Locations | Notes |
|---|---|---|
| 16x25x1 | Craftsman bungalows, ranch homes, townhomes | Most common Portland size for standard furnaces |
| 20x20x1 | Split-levels and mid-century homes | Often paired with wall returns in SE Portland and Gresham. |
| 20x25x1 | Newer construction (Bethany, Happy Valley) | Supports higher airflow for multi-story homes. |
| 16x20x1 | Condominiums & smaller furnaces | Verify airflow with higher MERV filters to avoid static pressure issues. |
| 16x25x4 / 20x25x4 | Homes with media filter cabinets | Popular in premium installations; lasts 6–12 months. |
| Return grille filters (custom) | Historic homes with odd-sized returns | Custom orders available—measure carefully and order in advance. |
MERV Ratings Explained
Minimum Efficiency Reporting Value (MERV) indicates how well a filter captures particles. Portland homeowners should balance filtration against airflow to protect both health and equipment.
| MERV Rating | Captures | Best For | Replacement Frequency |
|---|---|---|---|
| MERV 8 | Pollen, dust mites, lint | Basic protection; renters; short-term rentals | Every 30–60 days |
| MERV 11 | Pet dander, mold spores, auto emissions | Standard recommendation for most Portland families | Every 45–75 days |
| MERV 13 | Smoke particles, bacteria, sneeze droplets | Wildfire smoke season, asthma/allergy households | Every 30 days during smoke events |
| MERV 16 | Most airborne viruses, fine particulate | Medical sensitivities, home clinics, HEPA-level needs | Every 30–60 days; ensure system can handle pressure |
Portland-Specific Recommendations
We’ve maintained thousands of systems across Multnomah, Washington, and Clackamas counties. These best practices keep air healthy during wildfire smoke, pollen spikes, and damp winters.
Replacement Schedules & Reminders
Use these guidelines as a starting point. Smart thermostats (Ecobee, Nest, Honeywell) allow custom reminders tailored to your home’s usage patterns.
| Household Scenario | Recommended Frequency | Notes |
|---|---|---|
| Standard Portland household (no pets) | Every 60 days October–May, every 45 days June–September | Increase to monthly during wildfire smoke alerts. |
| Homes with pets or allergy sufferers | Every 30–45 days year-round | Use MERV 11 or 13 and log reminders in smart thermostat. |
| Media filters (4- or 5-inch depth) | Every 6 months; inspect quarterly | Replace sooner if static pressure exceeds manufacturer limits. |
| Vacation rentals / extended travel | Replace immediately before departure and upon return | Set smart thermostat alerts to remind property managers. |
Where to Buy Filters & Subscription Options
Choose the source that fits your lifestyle. Many Portland homeowners combine subscription deliveries during smoke season with professional installation during maintenance visits.
Efficiency Heating & Cooling Comfort Club
Filter delivery included with membership
We deliver the correct size, install during tune-ups, and dispose of old filters—no storage needed.
Local Hardware Stores (Home Depot, Lowe’s, Ace)
Same-day pickup for standard sizes
Check seasonal stock during smoke season. Inspect packaging to ensure filters are not crushed.
Online Subscription Services (FilterBuy, Amazon Subscribe & Save)
Automatic shipping every 30–90 days
Set frequency reminders for smoke season. Many services offer custom sizes with short lead times.
Wholesale HVAC Supply (Johnstone, Ferguson)
Bulk pricing for multi-family or large homeowners
Requires contractor account or partnership; Efficiency Heating & Cooling can source and deliver.
Furnace Filter FAQs for Portland Homeowners
Related Portland HVAC Services
Furnace Maintenance Plans
Filter changes, combustion analysis, and airflow checks included.
Indoor Air Quality Upgrades
Media cabinets, air scrubbers, and UV lights to enhance filtration.
Furnace Installation
New systems sized with appropriate filter cabinets and duct upgrades.
Heat Pump Maintenance
Tune-ups that coordinate furnace filter schedules with heat pump operation.
Portland Homeowners Trust Our Filter Expertise
Need a Filter Plan Before Wildfire Season?
We’ll measure, recommend the right MERV rating, set up delivery reminders, and install filters during tune-ups—so your Portland home stays protected year-round.
Serving Portland, Beaverton, Tigard, Lake Oswego, West Linn, and surrounding metro communities. Licensed • Bonded • Insured • CCB #187834.