Thermo-Sash 3e™ Pet Door for Sash Windows

Thermo-Sash 3e™ Pet Door for Sash Windows

As low as $419.00
In stock

The Endura Flap Thermo-Sash 3e™ Sash Window Pet Door includes...

  • Durable and insulating pet door for windows due to the dual-pane, LoE glass, and sturdy aluminum framing
  • Various flap sizes, colors, and adjustment ranges to fit your pet and your window
  • No tools required for installation, perfect for renters and vacation homes


Size Chart

Flap Size Flap Dimension Height To Raise Window    
Small 6" w x 11" h 18 1/2"    
Medium 8" w x 15" h 22 1/2"      
Large 10" w x 19" h 26 1/2"    
Extra Large 12" w x 23" h 30 1/2"    


Adjustment ranges include...

22"-25"          25"-28"          28"-31"          31"-34"          34"-37"          37"-40"          40"-43"

Important Note

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

Our normal 90 day return policy and 15 year warranty applies to Small, Medium and Large sizes as well as all other adjustment ranges


Popular Features Include...

  • Highly insulating flap with a complete magnetic seal, designed to stay closed in winds up to 50mph. Flap is made out of a polyolefin-based polymer which can keep your home comfortable in temperatures between -40 and 110 degrees fahrenheit
  • Dual-pane, LoE glass gives you extra insulation for your home, pairs perfectly with newer energy efficient windows
  • Fits all vertical sliding sash window widths between 22”-43” with a track width of at least 1“
  • 4 sizes available to fit cats to large breed dogs (NOTE: Endura Flap medium, large and extra-large sizes are not recommended for use by kittens or tiny dogs)
  • 3 color options including white, satin, and bronze (very dark brown)
  • Includes a draftstopper and weatherstripping for extra insulation and weather resistance
  • Can be installed and removed in seconds due to the spring loaded design, no tools required
  • 90 day return policy for Small, Medium, and Large sizes as well as all adjustment ranges besides 22”-25”
  • 15 year warranty for all pet doors
  • 100% made in the USA

There has been lots of discussion as to why the Endura Flap is such a high performing pet door, but for engineers or those looking for some more technical information here is a 74-page dog door energy efficiency study showing what makes it so special.

Replacement Parts and Accessories

Replacement Flap          Locking Cover          Height Extension          Weatherstripping          Draftstopper          Installation Kit

Endura Flap Pet Door Warranty

To the original purchaser, Endura Flap Pet Doors warrants this product and all of its component parts to be free of defects in materials or workmanship for a period of 15 years from the date of delivery to the customer.

Endura Flap assemblies employed in commercial kennels are warranted for a period of 3 years.

Damage caused by accident, improper installation, abuse or normal wear, including damage by pets or glass breakage is specifically excluded from this warranty. Defective materials returned to Endura Flap Pet Doors together with proof of purchase, will be repaired or replaced and returned to the customer free of charge.

Installing a Thermo Sash 3e


Design of the Endura Flap®


Variable Magnetic Resistance



Replacing the Flap in the Sash Pet Door



Switching Flap Sides


Wind Test


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