Free U.S. Shipping & Lifetime Warranty For All Endura Flap Pet Doors

  • Lets your cat come and go without opening the window
  • Helps maintain indoor comfort in hot and cold weather
  • Installs in seconds with no permanent changes
  • Magnetic seal supports a consistent flap closure
  • Adjustable panel fits a range of sash window sizes
  • Includes locking cover for added security when needed
  • Built in the USA with durable materials for daily use

Thermo Sash 3e Cat Door for Sash Windows

Freedom Through the Window

20 Reviews
Made in the USA USA flag icon
Regular price $419.99 USD

Fast & Free Shipping in the USA.

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Lifetime Warranty

Color: White
Width Adjustment Range


Give cats and dogs easy window access without sacrificing comfort using an insulated sash insert with magnetic sealing, spring-loaded compression fit, and built-in locking cover.

Installation & Fit

  • Fits vertically sliding sash windows with a track width between 22 inches and 43 inches and at least a 1 inch thick track. Here is a guide on how to properly measure your window
  • Works with traditional sash windows that slide up and down.
  • Slides into the existing window track and secures using a spring loaded compression design.
  • Stays in place through pressure within the track rather than permanent fasteners.
  • Includes a top loading locking cover that inserts directly into the pet door frame.
  • Extra Large 22 inch to 25 inch width panels are built with plexiglass and made to order.
  • Height needed to raise window per flap size
    Small - 18 1/2"
    Medium - 22 1/2"
    Large - 26 1/2"
    Extra Large - 3 1/2"

Best Suited For

Ideal for:

  • Renters and homeowners who want pet access without altering doors or cutting into walls
  • Homes where preserving insulation and minimizing drafts around a window opening is important
  • Cats that prefer a lower step through opening within a window location
  • Vacation homes or seasonal spaces where a semi permanent solution is preferred
  • Households that want to remove or adjust magnets to fine tune flap resistance for timid pets
  • Owners who value a locking cover for added security when pets need to stay inside
  • Access to a catio enclosure

Not ideal for:

  • Very narrow windows under 2 inches wide
  • Medium - Large size dogs. We recommend the Pet door for Sash Windows instead for larger flap size options
  • Horizontal sliding windows that open side to side where a horizontal insert such as Liberty Pet Door for Horizontal Sliding Windows would be more appropriate
  • Windows that cannot open high enough to accommodate the full outside frame height of the panel which varies by flap size

Questions

What's in the box?

  • 1 Sash Window Pet Door
  • 1 Foam Weather Strip
  • 1 Center Post Weather Seal Draft Stopper

Do I need tools to install the Thermo Sash Window Pet Door?

No. The panel installs using a spring-loaded compression design that expands to fit tightly within the window track. This allows quick installation without cutting or permanently modifying the window.

What type of windows does the Thermo Sash Pet Door fit?

This pet door is designed for traditional vertical sliding sash windows. It fits window track widths roughly between 22 and 43 inches with at least a 1-inch thick track.

How does the Thermo Sash Window Pet Door work?

The Thermo Sash Window Pet Door installs directly into the track of a vertically sliding sash window. The window closes down against the insulated panel, allowing your pet to use the built-in flap while maintaining a sealed window opening.

Explore all questions
Product Details

Product Details

This insert is built specifically for vertical sliding windows, allowing you to add a pet door without cutting into walls or doors. It sits cleanly within the window track, preserving the look and function of your home.

Quick Setup No Commitment
The spring-loaded design holds the panel in place using pressure within the track, so installation is fast and removal is just as easy. This makes it especially useful for renters or anyone who wants flexibility without permanent changes.

Comfort Through Every Season
The insulating glass panel helps reduce energy loss, while the magnetic-sealing flap returns into place after each use. Together, these elements help limit drafts and maintain a more stable indoor environment.

The aluminum frame provides structure and durability, while the flap is designed to remain flexible across a wide range of temperatures. This ensures consistent performance even with frequent use.

Flexible for Your Setup
The adjustable width allows the panel to fit a variety of window sizes, and the flap orientation can be configured to suit your space. For elevated windows, adding a step or ramp can make access easier for your cat.

Sizing & Fit

Size Chart

Flap Dimensions:

6"w x 11”h

The entry way your dog goes through.
flap dimensions
Height To Raise Window

Height To Raise Window

18 1/2"

How high you must raise your window in order to fit the panel into the track.
Flap SizeFlap DimensionHeight To Raise WindowRecommended Pet Height
Small6" w x 11" h18 1/2"9" - 15"

Important Note: All Extra Large and 22"-25" adjustment range sales are final, no returns. Please simulate the opening (open the window, use duct tape to simulate the opening) to be sure this size is appropriate before ordering.

Installation Guide

Installation Information

Installation icon Difficulty Easy
Installation icon Steps 4
Installation icon Time Required 0.5 hours

Parts

  • 1 Sash Window Pet Door
  • 1 Foam Weather Strip
  • 1 Center Post Weather Seal Draft Stopper

Tools

  • Flathead Screwdriver

Please read instructions & notes thoroughly before installation.

Step 1 Release Spring Mechanism

Release Spring Mechanism
  • Loosen the width adjustment locks at the end of the pet door insert with the screwdriver. This allows the spring mechanism to move freely from side to side.

Step 2 Check Panel Fit

Check Panel Fit
  • Insert the sash into the window track. Push against the spring mechanism and swing the opposite end into the opposite window track. Gently release. Tighten the width adjustment locks.

Step 3 Apply Weatherstripping

Apply Weatherstripping
  • Once you're sure the panel fits, remove it from the frame and lay it on its side on the ground.
  • For foam weatherstripping: Peel the backing off the foam weatherstripping. Press it along both edges of the panel, trimming as needed with scissors to ensure a snug fit.
  • For rubber weatherstripping: Clean the edge of your sliding door or window with rubbing alcohol to help the weatherstripping stick properly. Starting at the top or bottom, peel and press the strip into place with the folded edge facing indoors—align angled cuts if you have two pieces. For best results, apply the seal to the sliding door or window, but it can go on the pet door panel if needed.
  • Foam weatherstripping is applied onto both sides of the panel, but the rubber weather stripping only applies on the side of the slider door. Your panel will come with one type of weather stripping. You do not need both types.

Step 4 Mount Seal Draft Stopper

Mount Seal Draft Stopper
  • Mount the Center Post Weather Seal Draft Stopper. This strip prevents air from leaking between the window frame when raised to accommodate the sash. Trim to fit with scissors.
  • Put the panel back into the window track. Tighten width adjustment locks.
Videos

Videos

Endura Flap High-Quality Design


Endura Flap Impact Test


Leaf Blower Test


Variable Magnetic Resistance


How to Remove Side Magnets for Easier Use


FAQs

FAQ

Reviews

Customer Reviews