Endura Flap Thermo Sash 3e Cat Doors for Sash Windows

Regular price
Sale price
Regular price
Sold out
Unit price

  • Energy efficient cat door for windows with dual-pane, Low-E glass
  • Installs in sash windows 22" - 43" in width and at least a 1" thick track
  • Spring-loaded design does not require any tools for installation
  • Flexible flap remains secure and reliable in -40 degrees Fahrenheit temperatures and 50 mph winds
  • Available in white, brushed aluminum, or bronze (black)

For people who don't have the option of installing a cat door in a door or wall, the Thermo Sash Cat Doors for Windows provide a simple fix without any permanent alterations to your home. These window cat doors feature a highly insulating, weather-tight panel that installs into a wide range of sash windows without the need for any tools. No matter the season, your cat can experience free range without compromising your home's insulation in severe weather conditions.  If you need a larger flap size you will find them on the Endura Flap Thermo Sash 3e Pet Doors for Sash Windows page.


  • Extruded aluminum frame fits into windows from 22" - 43" in width and at least a 1" thick track.
  • Tool-free installation with spring-loaded design.
  • Dual-pane, Low-E glass panel ensures insulation and protects against harsh UV and infrared light.
  • Environmentally friendly, polyolefin-polymer flap stays securely sealed in 50 mph winds and -40 degrees Fahrenheit temperatures.
  • 6" x 11" flap size and adjustable step-over height accommodate cats of all breeds and sizes.
  • Adjustable magnets line the three sides of the flap for a tight, weatherproof seal. To adjust the magnet strength for easier training, refer to the 'Videos' tab for a short tutorial.
  • Includes a durable, ABS plastic locking cover.
  • Foam weather stripping and a draft stopper included for optimized insulation.



  • Removable design is ideal for vacation homes and rentals.
  • Avoid any permanent alterations of your home's construction.
  • Flexible flap does not pinch or snag during use.
  • Durability and thermal quality of the panel ensures longevity and eliminates heating/cooling loss.

Size Chart

Flap SizeFlap DimensionHeight to Raise Window
Small6" x 11"18 1/2"


Adjustment Ranges:

  • 22" - 25" Custom Order
  • 25" - 28"
  • 28" - 31"
  • 31" - 34"
  • 34" - 37"
  • 37" - 40"
  • 40" - 43"


Pet door has 1" framing, measure your track width to make sure that your window will accommodate the sash.

Final Sales: Adjustment Range 22" - 25" are final sale and cannot be returned. Final Sale products are made to order and will take extra time to ship.



Patio Pacific Inc Endura Flap Pet Door Lifetime Warranty

The Endura Flap lifetime warranty guarantees that any defective parts returned with proof of purchase will be replaced by the manufacturer for free. This excludes damage caused by accident, improper installation, overuse, or misuse—including damage by pets or glass breakage.

Additional Information

Flap Material


Your Maximum Pet Size


Installation Instructions

Installing the Thermo Sash 3e

Replacing the Flap in the Sash Pet Door

Switching the Flap Side

Installation Instructions for the Thermo Sash 3e Cat Doors for Sash Windows


  • Window pet door
  • Foam weather stripping
  • Center post weather seal draft stopper


Step 1: Loosen the thumb screws at the end of the sash. This allows the spring mechanism to move freely side to side.

Step 2: Insert the panel into the window track. Push against the spring mechanism and swing the opposite end into the opposite window track. Gently release. Tighten the thumbscrews. If the pet door sits properly, remove the pet door to put on the foam weather stripping in step 3.

Step 3: Apply the foam weather-stripping by peeling back the paper and exposing the adhesive. Unroll it along the edge of the panel, pressing to ensure it adheres. Install on both the top and the bottom. Trim to fit with scissors.

Step 4: Mount the draft stopper vinyl weather strip. This strip prevents air leaking between the window frame when raised to accommodate the sash. Trim to fit with scissors.


For a permanent lock, install a wood screw in the track immediately above the window on both sides. You will no longer be able to raise the window.

For a temporary lock, place a removable wooden dowel or charley bar in either track above the window.


Remove the screws on the top and bottom closest to the edge of the pet door. Then slightly loosen the screws closest to the glass. Next, slide off the side piece, then the flap assembly. Rotate the flap assembly (essentially flipping it upside down) then slide it back in. Make sure the locking cover is on the same side as the thumb screws. Replace the end spacer and screws.


Make sure you place steps or ramps leading to your pet’s door at a height that works. When they go through the flap, the top of the flap should be at least 1” (2,5 cm) higher than the top of their back. Watch your pet and adjust as needed to keep them comfortable.


If your window is thicker than 1 inch, your locking cover may hit the overhanging window. If you cannot place the sash flush with the inside track wall, you might not be able to install your thermo sash with the locking cover in place.


You will first need to loosen the thumbscrews, you may first need to lift the pet door up to loosen the bottom screw. Then compress the window pet door and tighten the thumbscrews once again for easy removal.

For help with installation, replacement parts or other questions visit or call 805-781-7700 Monday-Friday 7am-4:30pm PT.


How to Measure Your Sash Window for a Pet Door

Design of the Endura Flap

Adjusting Magnet Strength for Training

Leaf Blower Test


What do I need to know/measure before I order?

First raise up your window and check that it can go up far enough to be left with an opening 18 1/2" high. Next measure the width of the track from left to right, including going inside the track on both sides. Last measure how wide the track is that the window slides in (needs to be at least 1")

How wide does the track have to be for the Thermo Sash 3e to fit?

Track width needs to be at least 1" thick.

Can I choose what side the door is on?

It comes standard on the left, if you are looking from the inside of the house. You can switch it to the other side if you need and that only requires a screwdriver.

Is this easy to install?

This is designed to be a fairly simple install that does not require any tools. Take a look at the video under the installation tab to see if it something you would be able to do.

Will this door be good for more extreme weather?

The Thermo Sash 3e has the Endura Flap which is far better in sealing and durability than other models. Dual pane lo-e glass offers superior insulation value. Therefore, the Thermo Sash will be a much more reliable and longer lasting option then the more inexpensive options.

Is it possible to make one that fits a window smaller than 22"?

We can, the only thing is that we would not be able to use glass so there would be quite a bit of aluminum and some customers are not happy with the aesthetics. This would also fall under the custom and non-returnable category.

My cat is having a hard time opening the flap is there something I can do that would make it easier?

You can by removing some of the magnets. On the videos tab check out the "Adjusting Magnet Strength for Training."

What if I mis-measured?

If you've mismeasured, you may be able to fix it. To make your sash cat door about 1" wider, you may purchase a width extension (or make your own using 1" x lumber). To make your window kitty door insert slightly shorter you may trim the side flanges on the spring loaded adjustment piece with a hacksaw or a jigsaw with a metal cutting blade.

What does custom mean?

Any of the Thermo Sash doors with "Custom" listed means that the door is built to order and therefore it is non-returnable.

Can I get a custom height?

We can only do custom widths, not custom heights.

Customer Reviews

Based on 20 reviews Write a review