Where Is the Janitrol Furnace Filter Located

Finding the furnace filter location in a Janitrol system can be confusing because Janitrol furnaces were manufactured under several designs and installed in various configurations. This article explains common Janitrol filter placements, how to access and replace filters, and troubleshooting tips to keep systems running efficiently.

Janitrol Model Or Installation Type	Typical Filter Location	Notes
Upflow/Counterflow Cabinet Furnaces	Return Air Plenum Or Lower Cabinet	Often behind a removable access panel; filter may be horizontal or vertical
Downflow Furnaces	Top Of Furnace Or Return Plenum	Filter may sit in a slide-in rack beneath the coil
Strip-Mounted Or Wall Furnaces	Behind Front Access Panel	Smaller disposable or reusable screens
Air Handler Or Retrofit Installations	In Ductwork Near Furnace Return	Filter rack may be in return trunk or a remote filter box

Why Filter Location Matters For Janitrol Furnaces

The location of the furnace filter affects airflow, efficiency, and maintenance frequency. Janitrol systems often serve older homes and commercial spaces, and installers placed filters where space and duct layout allowed. Knowing the exact filter location helps prevent poor airflow, short cycling, and premature equipment wear.

Typical Filter Types Used With Janitrol Units

Janitrol furnaces can use a variety of filter types depending on installation: disposable fiberglass or pleated filters, washable electrostatic filters, and simple wire mesh or screen filters for strip-mounted units. Filter thickness commonly ranges from 1/2″ to 4″, with modern retrofits often using 1″ or 4″ pleated filters in a rack.

How To Identify The Filter Location Step-By-Step

Locate the return air duct and the furnace cabinet orientation first. In many cases, the filter sits between the return duct and the furnace blower. Follow these steps to identify the filter location reliably.

1. Turn Off Power To The Furnace: Switch off the furnace breaker or thermostat to prevent the blower from running while inspecting.
2. Find The Return Air Grille Typically on a wall, ceiling, or dedicated return trunk. Trace that duct toward the furnace cabinet.
3. Inspect The Furnace Cabinet Look for removable panels on the lower or front face of the furnace. Some panels are secured with screws or clips.
4. Check Top And Bottom Of Unit Filters may slide into a rack at the top (downflow) or bottom (upflow) of the cabinet. A filter may also be externally mounted in a separate return plenum.
5. Open Panels Carefully Hold loose panels and note any internal foam seals or gaskets to ensure proper reinstallation.

Common Janitrol Filter Locations Explained

Return Plenum Mounted Filters

When the furnace is connected to a return plenum, the filter often sits in a slot at the plenum inlet. This placement lets the filter treat all incoming air before it reaches the furnace coil and blower. Advantages include easier access and reduced duct contamination.

Cabinet Or Internal Slide-In Filters

Many Janitrol units have a filter rack inside the cabinet accessible via a front or lower panel. These filters commonly slide in vertically or horizontally and can be 1″ to 4″ thick. Replaceable pleated filters are frequent in retrofits.

Top-Mounted Filters On Downflow Units

Downflow furnaces often have filters at the top of the cabinet. The filter may be in a pull-out drawer or behind a top access panel. This arrangement works well when the return duct is above the unit.

Wall Or Strip-Mounted Filter Screens

Smaller wall-mounted Janitrol units use a simple screen or small disposable filter behind a front cover. These are usually smaller, less efficient filters and require more frequent cleaning or replacement.

How To Remove And Replace A Janitrol Furnace Filter

Replacing a filter is straightforward but differs by location and model. Follow these general steps and consult any available furnace documentation before proceeding.

1. Power Off Cut power to the furnace and turn off the thermostat fan setting.
2. Access The Filter Remove screws or release clips from the access panel. Gently pull the panel away and note panel orientation for reinstallation.
3. Slide Out The Old Filter Note filter direction: the airflow arrow should point toward the furnace blower/coil. If no arrow is present, air moves from the return side into the furnace.
4. Clean The Slot Vacuum dust from the filter slot and inspect for signs of moisture or mold. Address any leaks before inserting a new filter.
5. Install The New Filter Insert a correctly sized filter with the arrow pointing toward the furnace. Ensure a snug fit to prevent bypass.
6. Reattach Panel And Restore Power Reinstall the access panel and screws. Turn the furnace breaker back on and test operation.

Filter Sizing And Choosing The Right Type

Choosing the right filter requires matching size and MERV rating to the furnace and home needs. Janitrol systems may have nonstandard openings, so measure the filter slot precisely. Common sizes include 16x20x1, 20x25x1, and custom dimensions for older units.

Select a MERV rating appropriate for the household. MERV 6–8 provides basic protection for dust and lint, while MERV 11–13 captures finer particles but may reduce airflow if the blower isn’t sized for higher resistance. Consult an HVAC technician before increasing MERV on older Janitrol systems.

Retrofits And Upgrades For Better Filtration

Many Janitrol systems benefit from retrofitted filter racks or media filters installed in the return duct. Upgrades can include 1″ pleated filters, 4″ media cabinets, or a remote filter box upstream of the furnace. Benefits include better indoor air quality and longer filter life, but installers must ensure proper airflow and static pressure.

Troubleshooting When The Filter Is Not Where Expected

If the filter cannot be found in typical locations, several possibilities exist: the unit may use a panel-mounted screen, the filter may be located in a remote return box, or previous owners removed the filter during conversion. Inspect the ductwork upstream and check for a filter rack in the return trunk.

Signs the filter is missing include excessive dust buildup, dirty blower wheel, yellowing of heat exchanger areas, and reduced airflow. If these signs appear, schedule an inspection and clean the system before adding a new filter.

Maintenance Frequency And Best Practices

Maintenance frequency depends on filter type, household conditions, and usage. Disposable 1″ filters typically require replacement every 1–3 months. Pleated 4″ filters may last 6–12 months. Washable filters should be cleaned every 1–3 months.

Best practices include marking the filter installation date on the filter frame, checking the filter monthly during heavy use, and using a filter size and MERV rating compatible with the system. Regular filter maintenance extends furnace life and improves efficiency.

Safety And Precautions When Servicing Janitrol Furnaces

Safety is critical: always shut off power to the furnace and avoid disturbing the heat exchanger or ignition system unintentionally. Some older Janitrol units may have asbestos-containing gaskets or insulation; if suspected, stop work and consult a licensed professional for safe handling.

When in doubt about access panels, wiring, or combustion components, call a certified HVAC technician familiar with older equipment and retrofits to avoid damage or unsafe conditions.

When To Call A Professional

Call a professional if a filter cannot be located, if the blower shows signs of contamination, if there is unusual noise after replacing a filter, or if the furnace exhibits combustion problems. A technician can verify proper filter sizing, inspect the ductwork for hidden filter boxes, and measure static pressure to ensure the chosen filter won’t impede airflow.

Resources And Documentation For Janitrol Systems

Because Janitrol brand information is fragmented, useful resources include old installation manuals, OEM parts diagrams, and HVAC forums where owners and technicians share model-specific tips. Local HVAC companies with experience on vintage systems can provide field knowledge that documentation lacks.

Parts suppliers that specialize in legacy furnace components may offer filter racks or aftermarket adapters to accommodate standard filters in nonstandard openings.

Quick Reference Checklist For Finding And Replacing A Janitrol Filter

• Turn off power to the furnace before inspecting.
• Trace the return duct to the furnace cabinet.
• Look for removable panels on the front, top, or bottom of the unit.
• Check the return plenum and trunk for an external filter rack.
• Note filter size and airflow direction before purchase.
• Vacuum the slot and surrounding areas when changing filters.
• Record replacement dates and monitor static pressure after upgrading filters.

This guide equips homeowners and technicians with the knowledge to locate, remove, and replace filters in most Janitrol furnace installations. Proper filter maintenance improves air quality, protects equipment, and reduces energy costs.