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

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

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$589.99
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$589.99
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White
Black
Brushed Aluminum

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  • Insulating sash window insert with built-in pet door
  • Suitable for windows 22" - 43" in width, with 1" thick track
  • 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
  • Video to explain how to measure sash window track width
  • Extra Large Flap 22" - 25" Width Panel is all metal (no glass)
  • Custom orders are made to your specifications and are non-returnable
  • Approximately one month to build your custom pet door; reach out to our customer service team for expedited shipping options

Product Details


The Endura Flap Thermo Sash 3e Pet Door for Sash Windows provides your pets with the freedom to come and go while maintaining your home's insulation and energy efficiency. This sash window insert features a built-in pet door, combining the elegance of a sleek frame with the reliability of a weatherproof, insulating panel.

The Endura Flap Thermo Sash 3e is designed to fit snugly into the track of most windows, with sizes available for windows ranging from 22" to 43" in width and at least 1" thick track. The easy-to-install, spring-loaded design ensures a secure fit without the need for permanent installation, making it an excellent choice for renters and vacation homes.

Crafted with a heavy extruded aluminum frame, the Thermo Sash 3e is available in white, dark bronze, and brushed aluminum, blending seamlessly with your existing window. The Low-E glass further enhances the insulating properties by reducing harmful UV and infrared light.

The heart of the Thermo Sash 3e is the flexible polyolefin polymer flap, designed to remain functional in temperatures as low as -40°F. Lined with magnets along the edges, the flap offers superior sealing, remaining shut during heavy winds and extreme weather conditions.

For added security and insulation, a locking cover and weather stripping are included with the Thermo Sash 3e. The product also comes with a 90-day return policy and a lifetime warranty, giving you peace of mind in your investment.

Please note that the Extra Large Flap 22" - 25" Width Panel is all metal (no glass in the panel), custom-made-to-order, and non-returnable.

Features:

  • Heavy extruded aluminum frame in white, dark bronze, and brushed aluminum
  • Flexible polyolefin polymer flap, functional in temperatures down to -40°F
  • Superior sealing with magnets lining flap edges
  • Locking cover and weather stripping included for enhanced insulation
  • Lifetime warranty and 90-day return policy
  • Sizes to fit windows from 22" - 43" in width and at least a 1" thick track. Customized sizes available

Benefits:

  • Sleek frame and color variety are complementary to many windows
  • The flexible flap is easy for pets to use
  • Polyolefin polymer flap is pet and environmentally friendly
  • Accommodates both dogs and cats
  • Multiple pets can use the door due to its taller and slimmer design
  • Temporary/semi-permanent installation is perfect for renters and vacation homes
  • Keep your pets inside or out with the locking cover
  • Gives pets the ability to come and go when they please

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 Dimensions:

8"w x 15"h

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

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.
flap dimensions
Height To Raise Window

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.
flap dimensions
Height To Raise Window

Height To Raise Window

30 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"
Medium8" w x 15" h22 1/2"9" - 21"
Large10" w x 19" h26 1/2"9" - 27"
Extra Large12" w x 23" h30 1/2"9" - 34"

For your adjustment range, you need to measure the length of your sash window track from the furthest left to right. The adjustment range of your pet door should ideally have your track length in the middle. Custom orders are subject to special restrictions.

Find The Best Pet Door Size For My Pet

A

Pet Height: inches

B

Pet Width: inches

Please fill the above fields.

Additional Information

Frame Material

Aluminum

Track Width Minimum

1"

Flap Thickness

7/8"

Warranty Period

Lifetime

Locking Cover Material

Molded ABS Plastic

Climate Suitability

Severe 4-Season

Ability to Lock Flap

Yes

Can Be Installed In

Sash Windows

Sealing Value

Very High

Installation Instructions

Installation icon Difficulty Easy
Installation icon Steps 04
Installation icon Time Required 0.5 hours
Installation icon Sections 01
Installation icon Flags 01

Parts

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

Tools

  • Flathead Screwdriver

Please read instructions & notes thoroughly before installation.

Step 1 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

  • 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

  • Remove panel from window track.
  • Apply the foam weather-stripping by peeling back the paper and exposing the adhesive. Unroll it along the edge of the sash, pressing to ensure it adheres. Install on both the top and the bottom. Trim to fit with scissors.

Step 4 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.

Switch the Side of the Flap

You can switch which side of the sash panel the pet door flap is on to best fit your home.

Step 1

  • 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.

Step 2

  • 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 width adjustment locks.

Step 3

  • Replace the end spacer and screws.

LOCKING YOUR WINDOW

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, shown in Detail 1.

HEIGHT OF YOUR WINDOW

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.

Videos

FAQ

What things should I measure/consider when choosing a cat flap door for my sash window?

Four things: 

  • 1. What size pet door your dog or cat will need
  • 2. How high you can raise the window (will it raise high enough to fit the pet door size you selected)
  • 3. The width of the window (from the deepest part of the left track to the deepest part of the right track)
  • 4. The width of the track (must be at least 1" to accommodate the Thermo Panel)
 

How do I determine the size of pet door my pet will need?

The door should be wide enough that it does not touch your pet's sides as they go through, and the top of the pet door should clear your pet's back by at least one inch. Take a look at our guide on how to measure your pet for more information. For a large cat door or dog door, make sure that the window you are installing in will accommodate the flap height you choose.

What makes the Thermo Sash 3e better than the other manufacturer's sash window pet doors?

The Thermo Sash includes the patented Endura Flap Pet Door which has a dual-layered flap employing magnets around the edges for superior sealability and insulation. It uses LoE glass for added insulating properties. Both of these are housed in a sturdy aluminum frame. It is made in the USA and backed by a lifetime warranty.

How wide does the window track have to be to accommodate the Thermo Sash 3e?

Your window track must be at least 1 inch wide for thermo sash 3e pet door installation.

Which Thermo Sashes are considered custom and are not returnable?

All Extra Large pet door sashes and any pet door size in a sash width with a 22"-25" adjustment range.

Can I move the flap on the Thermo Sash from the left side to the right?

Yes you can switch the side the pet door is on. You start by removing the screws on the top and bottom, then sliding the flap assembly out. Once it is removed you simply flip it upside down and slide it right back in. Next you put the screws back in, tighten them all down and you're finished. You'll want to make sure the thumb screws and locking cover are on the same side.

Can you make a Thermo Sash smaller than 22" wide?

You can make it 3/4" smaller by trimming the right side (spring loaded piece).

What tools are needed to install a Thermo Sash?

You will need a flathead screwdriver to install the thermo sash.

How high do I have to raise my window to install the Thermo Sash?

It varies based on the pet door size: Small is 19", Medium is 23", Large is 27" and Extra Large is 31" high.

I ordered a 22"-25" adjustment range and mis-measured. My window is 25.5" wide. Is there anything I can do?

We make a width adjustment which extends the width by 3/4". You can order Patio panel height extensions for additional height. You could also cut, paint and use a small piece of wood to extend the width.

Can I adjust the height of the Thermo Sash?

The Thermo Sash does not have an adjustable height. The height of the unit is determined by the height of the pet door.

Which window cat door insert will keep out the desert heat?

The most energy efficient one is the Thermo Sash 3e Pet Doors for Sash Windows.

What energy saving dog door window insert do you have?

The Thermo Sash 3e pet door is the most energy efficient pet door window insert on the market.

I see the Thermo Sash 3e Pet Door for Sash Windows, what side sliding window cat door do you offer?

There is a vertical version of the Thermo Sash called the Thermo Panel. I is available in the same four flap sizes. It has three standard height ranges. If your window is shorter, a custom panel can be made.

Do you make Doggie Doors for Windows?

Yes! The Thermo Sash is designed for windows that lift up and down. The Thermo Panel is designed for windows that slide left to right. Both are available in Custom sizes.

Can I install a dog door in window if the window is not at ground level.

Yes. We've seen many creative ways to help our dog access the window. Pet parents usually install steps or a ramp on both sides of the window to the doggy access the window. This may require training, but can be successful.

How much does shipping cost?

Shipping is calculated at checkout.

Warranty

Warranty Type: Lifetime

Duration: Lifetime of the product.

Coverage: Defects in materials and workmanship under standard regular use.

Exclusions:

  • Damage caused by misuse or not using the product as intended.

  • Improper installation.

  • Damage caused by chewing.

View the full Endura Flap warranty policy. 



Customer Reviews

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

White / Small / Custom Panel Width Edit

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

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 Dimensions:

8"w x 15"h

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

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.
flap dimensions
Height To Raise Window

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.
flap dimensions
Height To Raise Window

Height To Raise Window

30 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"
Medium8" w x 15" h22 1/2"9" - 21"
Large10" w x 19" h26 1/2"9" - 27"
Extra Large12" w x 23" h30 1/2"9" - 34"

For your adjustment range, you need to measure the length of your sash window track from the furthest left to right. The adjustment range of your pet door should ideally have your track length in the middle. Custom orders are subject to special restrictions.

Find The Best Pet Door Size For My Pet

A

Pet Height: inches

B

Pet Width: inches

Please fill the above fields.

Frame Material

Aluminum

Track Width Minimum

1"

Flap Thickness

7/8"

Warranty Period

Lifetime

Locking Cover Material

Molded ABS Plastic

Climate Suitability

Severe 4-Season

Ability to Lock Flap

Yes

Can Be Installed In

Sash Windows

Sealing Value

Very High

Installation Instructions

Installation icon Difficulty Easy
Installation icon Steps 04
Installation icon Time Required 0.5 hours
Installation icon Sections 01
Installation icon Flags 01

Parts

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

Tools

  • Flathead Screwdriver

Please read instructions & notes thoroughly before installation.

Step 1 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

  • 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

  • Remove panel from window track.
  • Apply the foam weather-stripping by peeling back the paper and exposing the adhesive. Unroll it along the edge of the sash, pressing to ensure it adheres. Install on both the top and the bottom. Trim to fit with scissors.

Step 4 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.

Switch the Side of the Flap

You can switch which side of the sash panel the pet door flap is on to best fit your home.

Step 1

  • 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.

Step 2

  • 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 width adjustment locks.

Step 3

  • Replace the end spacer and screws.

LOCKING YOUR WINDOW

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, shown in Detail 1.

HEIGHT OF YOUR WINDOW

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.

Videos

FAQ

What things should I measure/consider when choosing a cat flap door for my sash window?

Four things: 

  • 1. What size pet door your dog or cat will need
  • 2. How high you can raise the window (will it raise high enough to fit the pet door size you selected)
  • 3. The width of the window (from the deepest part of the left track to the deepest part of the right track)
  • 4. The width of the track (must be at least 1" to accommodate the Thermo Panel)
 

How do I determine the size of pet door my pet will need?

The door should be wide enough that it does not touch your pet's sides as they go through, and the top of the pet door should clear your pet's back by at least one inch. Take a look at our guide on how to measure your pet for more information. For a large cat door or dog door, make sure that the window you are installing in will accommodate the flap height you choose.

What makes the Thermo Sash 3e better than the other manufacturer's sash window pet doors?

The Thermo Sash includes the patented Endura Flap Pet Door which has a dual-layered flap employing magnets around the edges for superior sealability and insulation. It uses LoE glass for added insulating properties. Both of these are housed in a sturdy aluminum frame. It is made in the USA and backed by a lifetime warranty.

How wide does the window track have to be to accommodate the Thermo Sash 3e?

Your window track must be at least 1 inch wide for thermo sash 3e pet door installation.

Which Thermo Sashes are considered custom and are not returnable?

All Extra Large pet door sashes and any pet door size in a sash width with a 22"-25" adjustment range.

Can I move the flap on the Thermo Sash from the left side to the right?

Yes you can switch the side the pet door is on. You start by removing the screws on the top and bottom, then sliding the flap assembly out. Once it is removed you simply flip it upside down and slide it right back in. Next you put the screws back in, tighten them all down and you're finished. You'll want to make sure the thumb screws and locking cover are on the same side.

Can you make a Thermo Sash smaller than 22" wide?

You can make it 3/4" smaller by trimming the right side (spring loaded piece).

What tools are needed to install a Thermo Sash?

You will need a flathead screwdriver to install the thermo sash.

How high do I have to raise my window to install the Thermo Sash?

It varies based on the pet door size: Small is 19", Medium is 23", Large is 27" and Extra Large is 31" high.

I ordered a 22"-25" adjustment range and mis-measured. My window is 25.5" wide. Is there anything I can do?

We make a width adjustment which extends the width by 3/4". You can order Patio panel height extensions for additional height. You could also cut, paint and use a small piece of wood to extend the width.

Can I adjust the height of the Thermo Sash?

The Thermo Sash does not have an adjustable height. The height of the unit is determined by the height of the pet door.

Which window cat door insert will keep out the desert heat?

The most energy efficient one is the Thermo Sash 3e Pet Doors for Sash Windows.

What energy saving dog door window insert do you have?

The Thermo Sash 3e pet door is the most energy efficient pet door window insert on the market.

I see the Thermo Sash 3e Pet Door for Sash Windows, what side sliding window cat door do you offer?

There is a vertical version of the Thermo Sash called the Thermo Panel. I is available in the same four flap sizes. It has three standard height ranges. If your window is shorter, a custom panel can be made.

Do you make Doggie Doors for Windows?

Yes! The Thermo Sash is designed for windows that lift up and down. The Thermo Panel is designed for windows that slide left to right. Both are available in Custom sizes.

Can I install a dog door in window if the window is not at ground level.

Yes. We've seen many creative ways to help our dog access the window. Pet parents usually install steps or a ramp on both sides of the window to the doggy access the window. This may require training, but can be successful.

How much does shipping cost?

Shipping is calculated at checkout.

Warranty

Warranty Type: Lifetime

Duration: Lifetime of the product.

Coverage: Defects in materials and workmanship under standard regular use.

Exclusions:

  • Damage caused by misuse or not using the product as intended.

  • Improper installation.

  • Damage caused by chewing.

View the full Endura Flap warranty policy.