• Insulating sash window insert with built-in pet door
  • Features 3/16" clear safety glass which is 59% thicker than the standard for enhanced durability and increased energy efficiency
  • Easy installation and semi-permanent, ideal for renters
  • Locking cover included that loads from the top
  • Watch our handy video to see how to measure a sash window track width
  • Extra Large Flap 22" to 25" Width Panel is made with plexiglass

Endura Flap Custom Thermo Sash 3e Pet Doors for Sash Windows

All-Weather Magnetic Seals Block Harsh Drafts

Made in the USA USA flag icon
Regular price $846.00

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Color: White
Flap Size
Width Adjustment Range


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Custom-built to your exact sash window width, this tool-free spring-loaded insert pairs insulating safety glass with double-walled magnetic flap technology to give your pet year-round access that resists severe weather and freezing drafts.

The Endura Flap Custom Thermo Sash 3e Pet Door for Sash Windows delivers award-winning thermal insulation in a tool-free, non-permanent window insert. Built with a heavy-duty aluminum frame and dual-pane flap technology, it provides your pet with ultimate freedom while keeping your home secure and weather-tight.

Custom Sash Window Fit
Engineered to fit vertical sash window openings from 22" to more than 45" wide, this insert features built-in spring-loaded adjustment for a snug, draft-free seal. The non-permanent design requires window tracks at least 1" wide and installs without structural modifications, making it perfect for both homeowners and renters.

Extreme Weather Insulation
The patented polyolefin polymer Endura Flap remains flexible in temperatures down to -40°F. Magnetic closure strips line the flap edges to ensure a tight, wind-resistant seal that prevents drafts and maintains indoor energy efficiency.

Heavy-Duty Construction & Glass
Constructed with an extruded aluminum frame available in white or dark bronze, the insert utilizes single-pane safety glass to preserve natural light. Note that larger flap configurations with very narrow windows may require plexiglass inserts, or no glass at all.

Integrated Access Control
Each door includes weatherstripping and a sturdy top-loading Endura Flap Locking Cover, allowing you to quickly secure the flap and manage your pet's access when needed.

Installation & Fit

  • Custom built for vertical sash window openings measuring 22" to more than 45" wide with up to 3-1/2" of spring-loaded adjustment for a draft-free seal.
  • Requires vertical sash window tracks measuring at least 1" wide.
  • Constructed with heavy-duty extruded aluminum framing in white or dark bronze and single-pane safety glass.
  • Includes a top-loading Endura Flap Locking Cover and weatherstripping to fully secure the installation.
  • Tool-free DIY setup snaps directly into existing window tracks in under 5 minutes with zero drilling or permanent modifications.

Best Suited For

Ideal for:

  • Extreme weather and high-wind locations, featuring heavy magnetic seals rated for 50 mph winds and sub-zero freezing weather.
  • Exceptional durability and thermal insulation that eliminates cracking, yellowing, warping, and ongoing flap replacement costs.
  • Renters and homeowners seeking a fast, tool-free installation into window tracks measuring at least 1" wide.
  • Pets that will be comfortable pushing through a heavy-duty, double-walled insulated flap.

Not ideal for:

  • Very small, timid, or elderly pets who may struggle with the heavy magnetic flap tension: choose the lightweight Liberty Pet Door for Sash Windows for effortless access.

Questions

How long do Endura Flaps typically last?

The lifespan depends on usage and weather exposure, but Endura Flaps are designed to last significantly longer than standard vinyl flaps. Many homeowners only need to replace them after years of heavy use.

Can you lock the pet door?

It comes with a latched closing cover, and you slide that in on the inside of the house.

Does this insulate well in severe weather?

This door has superior insulating capabilities. The double flaps have magnets that seal all the way around, and will stay closed in wind gusts up to 50mph. The Low-e glass also compliments the insulating value of you new vinyl door. It is our #1 recommendation for extreme climates.

Explore all questions
Product Details

Product Details

The Endura Flap Custom Thermo Sash 3e Pet Door for Sash Windows delivers award-winning thermal insulation in a tool-free, non-permanent window insert. Built with a heavy-duty aluminum frame and dual-pane flap technology, it provides your pet with ultimate freedom while keeping your home secure and weather-tight.

Custom Sash Window Fit
Engineered to fit vertical sash window openings from 22" to more than 45" wide, this insert features built-in spring-loaded adjustment for a snug, draft-free seal. The non-permanent design requires window tracks at least 1" wide and installs without structural modifications, making it perfect for both homeowners and renters.

Extreme Weather Insulation
The patented polyolefin polymer Endura Flap remains flexible in temperatures down to -40°F. Magnetic closure strips line the flap edges to ensure a tight, wind-resistant seal that prevents drafts and maintains indoor energy efficiency.

Heavy-Duty Construction & Glass
Constructed with an extruded aluminum frame available in white or dark bronze, the insert utilizes single-pane safety glass to preserve natural light. Note that larger flap configurations with very narrow windows may require plexiglass inserts, or no glass at all.

Integrated Access Control
Each door includes weatherstripping and a sturdy top-loading Endura Flap Locking Cover, allowing you to quickly secure the flap and manage your pet's access when needed.

Sizing & Fit

Size Chart

Flap Dimensions:

6"w x 11"h

The entry way your dog goes through.

Small flap
Small frame
Small rough cut

Height To Raise Window:

18 1/2"

How high you must raise your window in order to fit the panel into the track.

Flap Dimensions:

8"w x 15"h

The entry way your dog goes through.

Medium flap
Medium frame
Medium rough cut

Height To Raise Window:

22 1/2"

How high you must raise your window in order to fit the panel into the track.

Flap Dimensions:

10"w x 19"h

The entry way your dog goes through.

Large flap
Large frame
Large rough cut

Height To Raise Window:

26 1/2"

How high you must raise your window in order to fit the panel into the track.

Flap Dimensions:

12"w x 23"h

The entry way your dog goes through.

Extra Large flap
Extra Large frame
Extra Large rough cut

Height To Raise Window:

30 1/2”

How high you must raise your window in order to fit the panel into the track.

Flap Size Flap Dimension Outside Frame Dimension Recommended Pet Height
Small 6"w x 11"h 18 1/2" 9" - 15"
Medium 8"w x 15"h 22 1/2" 9" - 21"
Large 10"w x 19"h 26 1/2" 9" - 27"
Extra Large 12"w x 23"h 30 1/2” 9" - 34"

 

Do not know which size to get? Here is a measurement guide to help you out

FAQs

FAQ

Reviews

Customer Reviews

Request Freight Quote

Track heights exceeding 106 inches (107" or higher) may require additional shipping charges. Please provide your contact information for a custom freight quote, and our team will follow up during normal business hours.