Free U.S. Shipping & Lifetime Warranty

Thermo Sash 3e Cat Door for Sash Windows

Thermo Sash 3e Cat Door for Sash Windows

Regular price
$409.99
Sale price
$409.99
Unit price
per 
White
Dark Bronze/Black
Brushed Aluminum

How to Measure This field is required.

  • Insulating pet door designed for sash windows
  • 3/16" clear safety glass ensures energy efficiency
  • Sturdy aluminum frame available in white, brushed aluminum, and bronze color options
  • Easy installation with a spring-loaded design, ideal for renters and vacation homes
  • Included Locking Cover and complete magnetic seal for security and weather resistance
  • Panels less than 22" will have no glass 

Custom Order | Ships in 1-3 Weeks | Non-Returnable

Holds Up to Harsh Weather Holds Up to Harsh Weather
Cats Love it Cats Love it
Five Minute Installation Five Minute Installation

Product Details

  • Perfect for sash windows: Thermo Sash 3e Cat Door is designed specifically for vertical sliding sash windows. For horizontal sliding windows, check out the window panel
  • Energy efficient: 3/16" clear safety glass reduces energy loss, pairing well with energy-efficient windows
  • High-quality materials: Aluminum frame ensures durability and longevity, with a choice of three colors to match your window and home decor
  • Flexible installation: Adjustable to fit window widths, with a minimum track width of 1"
  • Quick and easy setup: The spring-loaded design allows for installation and removal in seconds, no semi-permanent changes required
  • Weather resistant: Insulating flap with a magnetic seal withstands winds up to 50mph, and remains flexible in temperatures from -40°F to 110°F
  • Secure your home: Locking Cover made of molded ABS plastic ensures your home and cat's safety
  • Extra insulation and weather resistance: Draft stopper and weatherstripping included for added protection against the elements
  • Suitable for various climates: Severe 4-Season Climate Suitability makes it perfect for year-round use
  • Made in the USA: Quality and craftsmanship you can trust
  • Cats love it: Easy to learn and use, keeping your cat happy and independent
  • Five-minute installation: Hassle-free setup means more time to enjoy the benefits of your new cat door
  • Customizable: Flap can be switched from left to right to accommodate your specific needs
  • Supports window modification: Steps or ramps can be added for elevated windows, ensuring easy access for your cat
  • Lifetime warranty: Purchase with confidence, knowing your investment is protected

Need help Installing? Take a look at our Thermo Sash Installation page.

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.

Find The Best Pet Door Size For My Pet

calculator.jpg

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 Printable Version
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

Installing a Thermo Sash 3e


How to Measure Your Door for a Sash Window Pet Door


Variable Magnetic Resistance


Replacing the Flap in the Sash Pet Door


Switching Flap Sides


Additional Switch the Side of the Flap


Wind Test

FAQ

Does the Thermo Sash have an adjustable height?

No, the height of the small sash window unit is determined by the height of the pet door.

Can I still into this dog door into my window if my window is not at ground level?

Yes! You can install steps or a ramp on both sides of the window to ensure your dog has access.

Is there a way to switch which side of the Thermo Sash the flap is on (from the left to the right)?

Yes. Start by removing the screws on the bottom and top og the panel, then sliding the flap assembly out. Then you can simply flip the assembly upside down and slide it right back in. Put the screws back in and tightened them. Make sure the thumb screws and your locking cover are on the same side of the panel.

Is the Thermo Sash available in sizes narrower than 22” wide?

You can make the small sash window panel ¾” smaller by trimming the spring loaded piece on the right side. Otherwise, we may be able to make you a custom unit. Please contact customer service for more details.

How high does my window have to be raised in order to install the Thermo Sash?

It varies based on your pet door size and height:

  • Small is 19"
  • Medium is 23"
  • Large is 27"
  • Extra Large is 31"

What is the minimum width of the window track needed to accommodate the Thermo Sash 3e?

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

Is this for sideways sliding windows?

No, this insert is for sash windows, which slide up and down and not side to side. If you have a sideways sliding window, see the Endura Flap Cat Door for Horizontal Sliding Windows (which is also available for vinyl window frames).  

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.

Is this for sideways sliding windows?

No, this insert is for sash windows, which slide up and down and not side to side. If you have a sideways sliding window, see the Endura Flap Cat Door for Horizontal Sliding Windows.  

What makes the Endura Flap better than other pet doors?

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.

Warranty

Endura Flap products have a lifetime warranty against defects in materials and workmanship under standard regular use. Endura Flap® Pet Doors Are 100% Designed, Engineered, and Manufactured in the USA. They are handmade for quality work in San Luis Obispo, California. 

We will replace any defective parts at no cost to you. Defective parts may include incorrectly sized flaps, bent or dented frames, or improperly fitted parts.

Customers living outside of the continental United States are responsible for shipping costs as well as duties and taxes (if applicable) for any replacement parts or services covered under the warranty policy regardless of the replacement part or service's original cost.  

Important Note:

Endura Flap® pet doors have a lifetime warranty for normal wear & tear and manufacturing defects (dog-chewing is not covered).

Damage caused by not using the product as intended, improper installation, and chewing is not covered under this warranty.

Endura Flap Pet Doors used in a commercial application like a Kennel or Boarding facility have a three year warranty.

Customer Reviews

Customer Reviews
4.8 Based on 19 Reviews
5 ★
89% 
17
4 ★
5% 
1
3 ★
5% 
1
2 ★
0% 
0
1 ★
0% 
0
Write a Review Ask a Question

Thank you for submitting a review!

Your input is very much appreciated. Share it with your friends so they can enjoy it too!

Filter Reviews:
CG
04/04/2022
Cynthia G.

Thermo Sash 3e Pet Door for Sash Windows

I bought this door for the catio I built outside a bedroom window and it is exactly what I was hoping for. Keeps the cold out and the cat happy. Being able to change which side the flap is on is a huge bonus. It's a well designed window/pet door and built to last. I'm very glad I bought it!

BH
04/04/2022
Barbara H.

well made and so easy to install

This product is a life saver for me as I don't have to wake up to my cat crying to go out anymore. I have 3, one conquered it in about 2 weeks (I did put masking tape over the magnets to lessen the strength and I did prop the door open with a jar so that the cats get used to coming and going through it. My second cat is just on the verge and if I push his paw through, he can take it from there. My third is fickle and scared of everything, not sure he'll ever conquer but when the weather is nice and I don't need heat or air, I still prop the door open. I did build a little staircase out of paver stones on both sides to help them get thru and I have a small cat castle on both sides of window portion so that they can look thru while they try to figure it out. Yes, they are beyond spoiled. The window is very well made and we have had some crazy winds and it didn't effect it one way or another.

KL
03/15/2017
K. LaValle

happy kitty. works as advertised. yes you can swith the door to the other side.

very happy. had a little difficulty getting the screws out to switch the opening to the other side as they were in extremely tight. i also had to move one of the magnets on the bottom of the flap because it shifted during shipping and the door seal was not quite right. works great & i have a very happy kitty. i found out how to do these two things online. really easy to do, if you know how. i would ask the company to include the magnet adjustment & door switching in their general documentation that ships with the door. i did have to modify the metal edge of my window frame to allow clearance for the door cover to slide up & down. we used a dremel. this is a permanent modification to the window, so might not be the best solution for a renter. i have tried several kitty-door solutions & would return them. so far, this one is a keeper.

R
02/15/2016
Rally

Cats are happy.

All but one cat has gotten use to the new flap. Since it was for cats, they put in only one magnet in. One side doesn't always close tight and I have to help it. I'm thinking of asking for 1 more magnet. Overall, the door is very sturdy and helps keep the cold out. I would recommend it to anyone. It is pricey, but so far, I feel it's worth it.

A
01/19/2016
ally

excellent pet door

this pet door is absolutely worth it. it is definitely worth the money. it is easy to install and my cats learned how to use it without great difficulty

Thermo Sash 3e Cat Door for Sash Windows

White / 22" - 25" Edit

The Thermo Sash window dog door is aethsetically pleasing and build to last. It comes in a variety of sizes to fit many animals.

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.

Find The Best Pet Door Size For My Pet

calculator.jpg

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

track width minimum

1"

warranty period

Lifetime

Installation Instructions

Installation icon Printable Version
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

Installing a Thermo Sash 3e


How to Measure Your Door for a Sash Window Pet Door


Variable Magnetic Resistance


Replacing the Flap in the Sash Pet Door


Switching Flap Sides


Additional Switch the Side of the Flap


Wind Test

FAQ

Does the Thermo Sash have an adjustable height?

No, the height of the small sash window unit is determined by the height of the pet door.

Can I still into this dog door into my window if my window is not at ground level?

Yes! You can install steps or a ramp on both sides of the window to ensure your dog has access.

Is there a way to switch which side of the Thermo Sash the flap is on (from the left to the right)?

Yes. Start by removing the screws on the bottom and top og the panel, then sliding the flap assembly out. Then you can simply flip the assembly upside down and slide it right back in. Put the screws back in and tightened them. Make sure the thumb screws and your locking cover are on the same side of the panel.

Is the Thermo Sash available in sizes narrower than 22” wide?

You can make the small sash window panel ¾” smaller by trimming the spring loaded piece on the right side. Otherwise, we may be able to make you a custom unit. Please contact customer service for more details.

How high does my window have to be raised in order to install the Thermo Sash?

It varies based on your pet door size and height:

  • Small is 19"
  • Medium is 23"
  • Large is 27"
  • Extra Large is 31"

What is the minimum width of the window track needed to accommodate the Thermo Sash 3e?

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

Is this for sideways sliding windows?

No, this insert is for sash windows, which slide up and down and not side to side. If you have a sideways sliding window, see the Endura Flap Cat Door for Horizontal Sliding Windows (which is also available for vinyl window frames).  

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.

Is this for sideways sliding windows?

No, this insert is for sash windows, which slide up and down and not side to side. If you have a sideways sliding window, see the Endura Flap Cat Door for Horizontal Sliding Windows.  

What makes the Endura Flap better than other pet doors?

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.

Warranty

Endura Flap products have a lifetime warranty against defects in materials and workmanship under standard regular use. Endura Flap® Pet Doors Are 100% Designed, Engineered, and Manufactured in the USA. They are handmade for quality work in San Luis Obispo, California. 

We will replace any defective parts at no cost to you. Defective parts may include incorrectly sized flaps, bent or dented frames, or improperly fitted parts.

Customers living outside of the continental United States are responsible for shipping costs as well as duties and taxes (if applicable) for any replacement parts or services covered under the warranty policy regardless of the replacement part or service's original cost.  

Important Note:

Endura Flap® pet doors have a lifetime warranty for normal wear & tear and manufacturing defects (dog-chewing is not covered).

Damage caused by not using the product as intended, improper installation, and chewing is not covered under this warranty.

Endura Flap Pet Doors used in a commercial application like a Kennel or Boarding facility have a three year warranty.

Customer Reviews

Customer Reviews
4.8 Based on 19 Reviews
5 ★
89% 
17
4 ★
5% 
1
3 ★
5% 
1
2 ★
0% 
0
1 ★
0% 
0
Write a Review Ask a Question

Thank you for submitting a review!

Your input is very much appreciated. Share it with your friends so they can enjoy it too!

Filter Reviews:
CG
04/04/2022
Cynthia G.

Thermo Sash 3e Pet Door for Sash Windows

I bought this door for the catio I built outside a bedroom window and it is exactly what I was hoping for. Keeps the cold out and the cat happy. Being able to change which side the flap is on is a huge bonus. It's a well designed window/pet door and built to last. I'm very glad I bought it!

BH
04/04/2022
Barbara H.

well made and so easy to install

This product is a life saver for me as I don't have to wake up to my cat crying to go out anymore. I have 3, one conquered it in about 2 weeks (I did put masking tape over the magnets to lessen the strength and I did prop the door open with a jar so that the cats get used to coming and going through it. My second cat is just on the verge and if I push his paw through, he can take it from there. My third is fickle and scared of everything, not sure he'll ever conquer but when the weather is nice and I don't need heat or air, I still prop the door open. I did build a little staircase out of paver stones on both sides to help them get thru and I have a small cat castle on both sides of window portion so that they can look thru while they try to figure it out. Yes, they are beyond spoiled. The window is very well made and we have had some crazy winds and it didn't effect it one way or another.

KL
03/15/2017
K. LaValle

happy kitty. works as advertised. yes you can swith the door to the other side.

very happy. had a little difficulty getting the screws out to switch the opening to the other side as they were in extremely tight. i also had to move one of the magnets on the bottom of the flap because it shifted during shipping and the door seal was not quite right. works great & i have a very happy kitty. i found out how to do these two things online. really easy to do, if you know how. i would ask the company to include the magnet adjustment & door switching in their general documentation that ships with the door. i did have to modify the metal edge of my window frame to allow clearance for the door cover to slide up & down. we used a dremel. this is a permanent modification to the window, so might not be the best solution for a renter. i have tried several kitty-door solutions & would return them. so far, this one is a keeper.

R
02/15/2016
Rally

Cats are happy.

All but one cat has gotten use to the new flap. Since it was for cats, they put in only one magnet in. One side doesn't always close tight and I have to help it. I'm thinking of asking for 1 more magnet. Overall, the door is very sturdy and helps keep the cold out. I would recommend it to anyone. It is pricey, but so far, I feel it's worth it.

A
01/19/2016
ally

excellent pet door

this pet door is absolutely worth it. it is definitely worth the money. it is easy to install and my cats learned how to use it without great difficulty

Lifetime Warranty
Fast Shipping
100% Secure Checkout
Easy Returns