How to Install a Furnace Filter (1-Inch HVAC)

Aerostar 16x25x1 furnace filter pack — type shown; confirm exact size in product title

Installing a 1-inch furnace filter takes a few minutes. Size and airflow direction matter more than brand slogans. Here’s the practical way we walk customers through it at Caliza Home.

Before you start

  1. Confirm the size. Read the printed nominal size on the old frame (for example 16x25x1 or 20x25x1). Order that size — not a tape-measure fraction. Guide: how to measure a furnace filter.
  2. Have the new pack ready. A furnace filter 6-pack means the next swap is already on the shelf.
  3. Know MERV. Match MERV 11 or MERV 13 to what your furnace / air-handler manual allows. Comparison: MERV 11 vs MERV 13.

Step 1 — Find the filter slot

Look for a thin grille or slot at the furnace / air handler, or a wall or ceiling return. Open or unclip the cover. Don’t force a sealed panel you’re unsure about — check the equipment manual if needed.

Step 2 — Remove the old filter

Slide the old filter straight out. Note which face pointed toward the furnace / blower. If the frame is crushed or the media is gray and packed, you’re due for a swap (many homes change about every 90 days).

Step 3 — Check the airflow arrow

On the new frame, find the printed arrow. The arrow points with the airflow — toward the furnace / blower. Installing backward is a common mistake and reduces how well the pack seals and filters.

Step 4 — Slide the new filter in

Insert the filter so it sits flat in the rack with no big gaps at the edges. Don’t crush the cardboard frame to “make it fit.” If it won’t seat cleanly, you likely have the wrong nominal size — recheck the old label or see our 16x25x1 and 20x25x1 size hubs.

Step 5 — Close up and mark the date

Replace the cover. Write the install date (and size) on the frame with a marker. That makes the next 90-day swap obvious.

Quick checklist

  • Printed size matches the new pack
  • Arrow toward the furnace / blower
  • Frame sits flat — no forced crush
  • Date written on the frame

More help

Filter FAQ · Measure guide · MERV 11 vs 13

Caliza Home is a small Southern California shop. Our HVAC packs use the Aerostar line with manufacturing tied to Orlando, Florida factory operations for this line — we state factory city carefully. Not a medical device, not a water softener, no 99.9% claims.