Armstrong Air Furnace Filter Location and How to Access It

Finding the Armstrong Air furnace filter location is essential for maintaining airflow, indoor air quality, and system efficiency. This guide explains where filters are typically located on Armstrong furnaces, how to access and replace them, recommended filter types and sizes, maintenance tips, and when to seek professional help. It is designed for a general U.S. audience and focuses on practical, safe steps to keep an Armstrong furnace running well.

Common Armstrong Furnace Model	Typical Filter Location	Filter Type
Compact Upflow/Horizontal Models	Filter Rack At Blower Compartment Or Return Plenum	1″ To 2″ Disposable Or Washable
Downflow Furnaces	Filter Access Panel On Side Or Above Blower	1″ To 4″ Disposable Or Pleated
Cabinet-Integrated Units	Return Air Grille Or Inside Cabinet Slide-Out Rack	1″ To 5″ Pleated Or Media

Where Armstrong Furnace Filters Are Usually Located

Armstrong Air furnaces typically have filters located in one of three places: inside the furnace cabinet at the blower compartment, in the return-air plenum or duct directly adjacent to the furnace, or at a wall/ceiling return air grille. The exact location depends on the model configuration (upflow, downflow, or horizontal) and how the HVAC system is installed in the home.

Filter Location By Furnace Configuration

Upflow Furnaces

On upflow Armstrong furnaces the filter is commonly placed below the blower or beneath the return-air opening. This location often uses a slide-in filter rack accessible by removing a lower service panel or filter door.

Downflow Furnaces

Downflow models usually have the filter at the top of the furnace or within a dedicated access slot on the side. The filter may be reachable by removing an external panel or by accessing a return plenum attached above the unit.

Horizontal Furnaces

Horizontal installations often place the filter in the return plenum at the side of the cabinet or inside the blower compartment. The filter may slide into a horizontal rack and is sometimes accessed through a small removable access panel.

How To Identify The Filter Slot Or Rack

To identify the filter slot, look for a removable panel or rectangular slot sized for common filter dimensions. Labels or arrows on the furnace cabinet often indicate airflow direction and filter placement. If the filter is not in the cabinet, check return grilles in the nearest wall or ceiling or inspect the return plenum adjacent to the furnace.

Step-By-Step: Accessing And Replacing An Armstrong Furnace Filter

1. Turn Off The Furnace: Set the thermostat to “off” and switch the furnace power switch to the off position to prevent the blower from starting while servicing.
2. Locate The Filter Panel: Inspect the furnace front and sides for a removable panel, filter door, or slide-out rack. Check return grilles and the return plenum if the cabinet shows no obvious slot.
3. Remove The Panel Or Grille: Use a screwdriver if necessary. Keep fasteners in a safe place. For return grilles, depress the spring clips or unscrew the grille to reveal the filter.
4. Observe Filter Orientation: Note the airflow arrow on the filter frame. The arrow must point toward the furnace/blower (away from the return duct).
5. Remove And Inspect The Filter: Pull the filter straight out and inspect for dirt, dust, or damage. Compare the old filter size printed on its frame to the replacement.
6. Insert The New Filter: Slide the replacement filter into the slot with the airflow arrow pointing into the furnace. Ensure the filter sits flush and the panel closes securely.
7. Restore Power: Replace the panel or grille, restore the furnace power, and set the thermostat to the desired setting.

Filter Types And Sizes For Armstrong Furnaces

Armstrong furnaces accept a range of filter types and sizes. Common options include 1″ foam or fiberglass filters, 1″–2″ pleated disposable filters, and higher-efficiency 4″–5″ media filters or HEPA-grade options installed in dedicated housings.

Popular sizes include 16x20x1, 16x25x1, 20x20x1, 20x25x1 and thicker media sizes. Always confirm exact dimensions printed on the old filter or consult the furnace data plate and owner’s manual before buying replacements.

Recommended MERV Ratings And Considerations

For standard households, a MERV rating between 6 and 8 provides good particle capture without adding excessive pressure drop. Homes with pets, allergies, or smoke exposure may benefit from MERV 10–13 filters. Very high-efficiency filters (MERV 14–16 or HEPA) can restrict airflow if the system and blower are not designed for them.

When upgrading filter efficiency, consult an HVAC technician to confirm the furnace blower can handle the additional static pressure and to avoid reduced performance or system damage.

Maintenance Frequency And Best Practices

Filter replacement frequency depends on filter type and household conditions. Disposable 1″ filters typically need replacement every 1–3 months. Pleated 2″ filters last 3–6 months. 4″–5″ media filters can last 6–12 months. Homes with pets, smokers, or high dust should change filters more often.

Keep a maintenance checklist: check filters monthly during peak seasons, write the change date on the filter frame, and keep spare filters on hand. Regular filter changes help maintain efficiency and extend equipment life.

Troubleshooting Common Filter-Related Problems

Restricted Airflow And Poor Heating

A clogged filter reduces airflow, causing temperature swings, longer run times, and increased energy use. Replace the filter and verify airflow improves. If problems persist, check for duct leaks or a dirty blower wheel.

Noise Or Rattling After Replacement

Loose filter panels or improperly sized filters can cause vibration. Ensure the filter fits the slot snugly and that panels and grille screws are tightened.

Dusty Home Despite A Clean Filter

Persistent dust may indicate leaks in the return ducts, a dirty blower, or inadequate filter MERV. Inspect duct seals and consider professional duct cleaning or a higher-efficiency filter if the system can handle it.

Safety Tips When Handling Furnace Filters

• Always turn the furnace power off before accessing the filter compartment.
• Wear gloves and a dust mask if filters are heavily soiled.
• Dispose of disposable filters in sealed bags to limit dust spread.
• Avoid using water on disposable filters; only washable filters can be cleaned per manufacturer instructions.

When To Call An HVAC Professional

Contact an HVAC technician if the filter slot is inaccessible, if replacing the filter does not resolve airflow or heating problems, or if the homeowner suspects incorrect filter size or excessive static pressure. Professionals can assess blower capacity, test duct pressure, and recommend the correct filter type for the system.

Finding Model-Specific Filter Information

To find the exact filter location and specifications for a particular Armstrong Air furnace model, locate the unit’s model and serial number on the data plate. The owner’s manual or Armstrong’s online resources typically list recommended filter sizes and installation details. If the manual is unavailable, the model number can be used to search Armstrong’s documentation or to ask a dealer for guidance.

Common Mistakes To Avoid

• Installing The Filter Backwards: The airflow arrow must point to the furnace.
• Using Incorrect Size: A loose or forced fit reduces effectiveness and may allow unfiltered air bypass.
• Over-Filtering Without System Check: Installing very high MERV filters without confirming system compatibility can reduce airflow and efficiency.
• Neglecting Regular Checks: Waiting too long to inspect filters causes strain on the HVAC system.

FAQs About Armstrong Air Furnace Filter Location

How Often Should An Armstrong Furnace Filter Be Changed?

Typically every 1–3 months for 1″ disposable filters, 3–6 months for pleated filters, and 6–12 months for thicker media filters, depending on household conditions.

What If The Furnace Has No Visible Filter Slot?

Check return grilles and the return plenum. Some installations place the filter at a wall or ceiling return or inside a separate filter housing in the ductwork.

Can A Homeowner Use A Higher MERV Filter?

Yes, but confirm the furnace blower and duct system can handle the additional pressure drop. Consult an HVAC technician for systems that may be sensitive to higher-resistance filters.

Are Washable Filters Compatible With Armstrong Furnaces?

Washable filters can be used if they match the size and fit. They require regular cleaning but may not capture fine particles as effectively as high-quality disposable pleated filters.

Useful Resources And Further Reading

Owners should refer to the Armstrong Air owner’s manual, product data plate, and the manufacturer’s website for model-specific guidance. Professional HVAC associations and EPA resources provide additional information on indoor air quality and filter selection.

Key Takeaways

Most Armstrong Air furnace filters are located in the blower compartment, return plenum, or at a return grille. Correctly identifying the filter slot, matching filter size, and following the airflow arrow will ensure proper installation. Regular inspection and replacement improve efficiency and indoor air quality, while professional help is recommended for access issues or performance concerns.