Intertherm Furnace Filter Location and Replacement Guide

The Intertherm furnace filter location is a common search for homeowners maintaining HVAC systems. This guide explains where Intertherm furnace filters are typically located, how to identify the correct filter type, step-by-step replacement instructions, troubleshooting tips, and maintenance recommendations to keep the system running efficiently.

Intertherm Unit Type	Common Filter Location	Typical Filter Sizes
Upflow/Downflow Furnaces	Return air grille or furnace blower compartment	16x20x1, 20x25x1
Horizontal Furnaces	Side-access panel near blower or return opening	14x20x1, 16x20x1
Packaged Units	Air intake panel or return duct collar	Custom/ADA sizes

Why Knowing The Intertherm Furnace Filter Location Matters

Locating the Intertherm furnace filter is essential for airflow, efficiency, and indoor air quality. A correctly installed, clean filter reduces strain on the blower motor, lowers energy use, and helps prevent premature component failure. Many service visits and unnecessary repairs result from clogged or improperly placed filters.

Common Intertherm Furnace Types And Where Filters Are Located

Intertherm furnaces come in upflow, downflow, horizontal, and packaged configurations. The filter location varies by model and installation orientation. Identifying the furnace type helps narrow the likely filter access point.

Upflow And Downflow Furnaces

In upflow units the filter is usually at the bottom of the cabinet or in the return duct before the furnace. In downflow units the filter is often at the top or in the return air grille. Check both the return grill and the blower compartment access panel.

Horizontal Furnaces

Horizontal Intertherm furnaces frequently use a side-access filter slot near the blower motor or in an adjacent filter rack. The access panel may be held by screws or clips. Filters for horizontal installations sometimes differ in thickness and length.

Packaged Units And Rooftop Systems

Packaged Intertherm systems generally place filters behind a hinged intake or access door on the unit’s exterior. These filters may be larger or custom sizes; always confirm the filter dimensions before purchasing replacements.

How To Find The Filter: Quick Checklist

• Turn off power to the furnace at the switch or breaker.
• Inspect the return air grilles inside the home for a removable filter slot.
• Open the furnace access panels—bottom, front, top, or side depending on model.
• Look near the blower compartment and evaporator coil for a filter rack or slot.
• Check the owner’s manual or model data plate for filter size and location info.

Step-By-Step Filter Replacement For Intertherm Furnaces

The following general steps apply to most Intertherm furnace filter location scenarios. Always consult the specific unit manual when available.

Tools And Supplies Needed

• Replacement filter of correct size and MERV rating
• Screwdriver or nut driver (if panel fasteners are used)
• Flashlight
• Gloves and dust mask (recommended)

Replacement Steps

1. Power Down: Turn off power at the furnace switch or electrical panel to prevent the blower from starting while hands are inside the unit.
2. Locate Filter: Use the checklist to identify the filter slot at the return grille or in the furnace cabinet near the blower or coil.
3. Remove Access Panel: If the filter is in the furnace, remove screws or unclip the access panel. Keep hardware in a safe spot.
4. Slide Out Old Filter: Note the filter’s airflow direction arrow. Carefully slide out the old filter to avoid dropping dust into the cabinet.
5. Check Filter Frame And Slot: Look for debris on the filter rack, and vacuum if necessary to prevent dirt from entering the blower or coil.
6. Install New Filter: Insert the replacement filter with the arrow pointing toward the furnace (toward the blower). Ensure a snug fit without gaps.
7. Replace Panel And Restore Power: Secure the access panel and restore power to the unit. Turn on the system to confirm normal operation.

How To Identify The Correct Filter Size And Type

Filter sizes are usually printed on the filter frame. Common sizes used by Intertherm furnaces include 16x20x1, 20x25x1, and 14x20x1. If the old filter lacks markings, measure the slot length, width, and thickness and add 1/2 inch to each dimension when measuring the old filter frame will give accurate replacement numbers.

Filter type selection affects air quality and system performance. MERV 8 is a typical balance for residential systems; MERV 11–13 offers better filtration but may increase resistance in some older or low-capacity blowers. Always match the filter resistance rating to the furnace blower specifications.

Common Problems When Replacing Filters And How To Avoid Them

Improper filter installation or the wrong filter size can cause airflow restriction and system faults. Common issues include reversed airflow installation, using filters that are too thick to fit, and neglecting to secure access panels which can cause vibration, noise, or air bypass.

• Reversed Filter Direction: Install with arrow pointing toward blower; reversed placement reduces filtration and may damage the system.
• Wrong Size: Measure the filter slot; don’t guess. A loose filter allows unfiltered air to bypass.
• High MERV In Low-Capacity Systems: High-efficiency filters can restrict airflow if the blower cannot handle the additional resistance. Check blower capacity or consult a technician.

Maintenance Schedule And Best Practices

Frequency of filter changes depends on factors like household occupancy, pets, and air quality. A conservative schedule for Intertherm furnace filter location and replacement is every 1–3 months for 1-inch filters, and every 3–6 months for thicker pleated filters.

• Check filters monthly during heavy use seasons.
• Replace disposable 1-inch filters every 1–3 months.
• Replace pleated filters every 3–6 months or according to manufacturer guidelines.
• Consider higher-capacity filters if allergies are a concern, but confirm compatibility with the unit.

When The Filter Isn’t Where Expected

Sometimes the Intertherm furnace filter location is not obvious because installers place a remote filter grille in the return duct or closet. In split systems, the filter may be in the air handler or in a separate filter housing. If the filter cannot be located, consult the model’s specification sheet or contact a qualified HVAC technician.

Safety And Precautions

Always cut power to the furnace before opening access panels. Avoid forcing panels off, which can damage seals and screws. Use gloves and a mask if replacing heavily soiled filters to reduce exposure to dust and allergens.

Signs A Filter Change Is Overdue

Recognizing when the Intertherm furnace filter location needs attention prevents system damage. Signs include reduced airflow from vents, increased energy bills, abnormal furnace cycling, poor indoor air quality, and visible dust buildup around registers. If any of these are present, check and replace the filter promptly.

When To Call A Professional

Contact an HVAC technician when the filter is in the correct location but the furnace still shows low airflow, unusual noises, frequent cycling, or error codes. A technician can inspect the blower motor, evaporator coil, ductwork, and controls for issues beyond filter-related problems.

Replacement Parts And Where To Buy

Replacement filters for Intertherm furnaces are available from HVAC supply stores, home improvement retailers, and online marketplaces. For obsolete or custom-sized filters, contact the furnace manufacturer or a local HVAC service for recommendations. Keep the furnace model and serial number handy when ordering parts.

FAQ: Quick Answers About Intertherm Furnace Filter Location

How Often Should An Intertherm Filter Be Changed?

Most 1-inch filters should be changed every 1–3 months; pleated or higher-capacity filters may last 3–6 months depending on usage and air quality.

Can A Homeowner Replace The Filter?

Yes. Replacing the filter is straightforward for most Intertherm furnace filter location scenarios. Turn off power, locate the slot, and install the correct size and orientation. Contact a technician for complicated access or if unsure.

What If The Filter Slot Is Missing?

Some installations use remote filters in return ducts or dedicated filter cabinets. Check return grilles, ducts, and the air handler. Refer to the manual or contact a technician if the filter slot cannot be located.

Does Filter MERV Rating Affect Performance?

Higher MERV filters capture more particles but may restrict airflow in some systems. Choose a MERV rating compatible with the furnace blower; consult the manual or HVAC professional if uncertain.

Maintenance Log Template

Date	Action	Filter Size/Type	Notes
2025-01-01	Replaced Filter	16x20x1 MERV 8	Normal
2025-04-01	Checked Filter	16x20x1 MERV 8	Light Dust

Final Tips For Maintaining Intertherm Furnace Filters

Keep a spare filter in the home matched to the measured slot size. Label the furnace access panel with the filter size and recommended replacement interval. Periodic visual checks of the filter and surrounding components help maintain system efficiency and extend equipment life.