Endura Flap Custom Thermo Panel 3e for Windows

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  • Adjustable heights and custom sizes to fit any sliding window
  • Durable frame and pet door made to withstand extreme climates
  • Made with dual-pane, Low-E glass to improve energy efficiency
  • Tool-free installation 
  • All Customs are final sale and cannot be returned, please allow 3 – 4 weeks for custom models to be built and shipped
  • An email will be sent to you requesting additional information for your custom order

This is the custom window pet door for the Endura Flap Thermo Panel 3e for horizontal sliding windows of unusual heights. The track height adjustment ranges for custom orders are for windows under 74 3/4", between 80 1/4" 93 1/4", and over 96 1/4". Please note that custom-made Endura doors are non-refundable and non-returnable. The panels have a 3" spring-loaded height adjustment, so if you request a 40" panel, for example, the panel you receive will be adjustable from 38" to 41". The Thermo Panel 3e has a spring-loaded design that fits into your sliding window track without the use of any tools. It features dual-pane, Low-E glass to prevent UV rays and infrared light from entering your home. With a flexible, environmentally friendly flap lined on all three sides with magnets, heavy wind will be unable to blow through this window pet door. Save on heating and cooling with the insulating Endura Flap. 


  • Pet flaps come in small, medium, large, & extra large for any size pet
  • Flap dimensions designed to accommodate pets of multiple sizes
  • Aluminum frame designed to fit into the window track with a width of at least 1" thick
  • Available in white, brushed aluminum, and dark bronze (black)
  • Dual-pane, Low-E glass allows natural light to enter while blocking out unwanted UV rays and infrared light
  • Flap withstands -40 degree temperatures and stays sealed in 50mph winds
  • Magnetic sealing resists heavy winds/storms
  • Flap swings on a rod at the top, avoiding breakage
  • Includes a sturdy locking cover
  • C-Clamp Lock included for adjustment ranges under 74 3/4" to lock the slider


  • Removable panel benefits all owners, especially renters.
  • Don't have to make any permanent alterations to window
  • Available in white, bronze, or brushed aluminum to match your window
  • Pets can enter and exit as they please

Size Chart

Flap SizeFlap DimensionStep Over RangeOverall Panel Width
Small #66" w x 11" h3" – 5"11 1⁄4"
Medium #88" w x 15" h3" – 5"13 1⁄4"
Large #1010" w x 19" h3" – 5"15 1⁄4"
Extra Large #1212" w x 23" h3" – 7" (ships at 5")17 1⁄4"


Track Height Adjustment range is based on the measurement of your window height from the lowest point of your track to the highest point. Wondering how to measure your track? Review our Track Measuring Guide. Each Endura Flap Thermo Panel 3e for Windows has a 3" adjustment range with your window track height approximately in the middle.

Please note: If you order a custom insulated glass unit, it must be specially ordered which takes about 4 weeks. Since these are custom heights it is a final sale, no returns.

If your measured track height is near the bottom of the adjustment range then you should review A Note of Caution.

Minimum and Maximum heights vary by flap size. Here is the info: 

Custom Height: Minimum & Maximum Heights
Extra Large46"123"

Additional Information

Frame Material

Heavy Extruded Aluminum

Track Width Minimum


Flap Material

Engage Polyolefin

Flap Colors


Flap Thickness


Flap Warranty (if separate)

15 years

Dual or Single Pane

Dual Pane

Warranty Period

15 years

Return Period

Not Returnable

Locking Cover Material

Dimensional ABS

Your Maximum Pet Size

Cats, Large Cats, Small Dogs, Medium Dogs, Large Dogs, X-Large Dogs

Climate Suitability

Severe-4 Season

Type of Window

Sideways Sliding

House Locking Method

C-Clamp Lock

Flap Design

Single, One Part, Flexible, Insulated Flap

Can Be Installed In

Dual Pane Glass Sliding Glass Door, Sideways Sliding Windows, Single Pane Glass Sliding Glass Door, Vinyl-Framed Sliding Glass Door

Custom Heights Available


High Aspect Ratio


Award Winning Design


Sealing Value

Very High

Wind Resistance

Very High

Insulation Value


Installation Instructions


All Panels

  • 1x Foam Weather Strip
  • 1x Center Post Weather Seal Draft Stopper

1 Piece Pet Door

  • 1x Panel Pet Door
  • 1x Sliding Door Clamp

2 Piece Pet Door

  • 1x Top Glass Panel Section
  • 1x Bottom Flap Section
  • 4x Hex screws
  • 1x Hex wrench
  • 1x Threshold mount deadbolt with screws



The aluminum, vertical panel has a patented ‘Adjustable Step-Over’ feature which permits adjusting the height of the flap to the most comfortable fit for your pet. Generally, the top of the flap should be positioned to be at least 1” (2,5 cm) above the top of the pet’s shoulder (the ‘withers’). If the factory setting is not suitable, please adjust it before proceeding. If the current setting is suitable, or you have the vinyl panel, proceed to step 3.



Step 1A: Two-piece panels: Simply slide the pieces up and out from the bottom half of your panel to rearrange. Loosen a bottom screw if the pieces are too snug to move.

One-piece panels: Lay the entire panel on a flat surface (like the floor). Using a #2 Phillips head screwdriver, remove the bottom side-screws, and loosen the next upper screws one turn. Screws were tightly installed to hold the panel together during shipping; a drill is recommended*.

*If you do not have a Phillips head drill bit skinny enough to fit, let us know and we’ll send you one for free.

Step 2B: One-piece panels: Once the bottom screws have been removed and the next upper side-screws loosened, the Pet Door Assembly and spacers can be removed by sliding the sections down and out of the panel. 

Step 2C: Replace the spacers and the Pet Door Assembly by sliding them back in a different order to achieve the desired height. You can move the spacer below or above the flap to raise or lower the flap height.

The order of the pieces is important! The piece on the bottom needs to always be at the bottom, as that is where the screws attach. 

When finished, replace the bottom side-screws and tighten the next upper-side screws for one piece panels and skip to step 4. For two-piece panels, you can now assemble the patio panel!

Please Note: A lower step-over height is easier for pets to navigate. However, if the top of the flap is low enough that the pet needs to crouch to get through their pet door, they can injure themselves and possibly cause the pet door to malfunction. If your pet door does not sit at a comfortable height for your pet, you may need a larger size flap. 



(If you have a single piece panel, please proceed to step 4)

Step 3A: Align the aluminum connectors extending from the bottom flap panel section with the top glass panel section. Press the aluminum connectors into the holes at the bottom of the top glass panel section. Ensure locking cover & thumb screws are on the same side!

Step 3B: Gently tap the bottom surface of the panel against the ground to completely insert the connectors. Protect hard surfaces to prevent scratching. The components of the panel are designed to slide together very tightly.

Step 3C: Fasten the two panels together using the four stainless steel hex head screws found in the panel packaging. Use the hex wrench to tighten screws so the two halves of the door are pulled together.

Please Note: Screw holes may look misaligned; this is intentional to ensure a tight fit. The panels will squeeze together as the screws are tightened.

Step 4: Loosen the thumb screws at the top of the pet panel. This allows the spring mechanism to move freely up and down.

Step 5: To insert the panel pet door into the top track, push up against the spring mechanism and swing the bottom of the panel up and over the threshold. Seat the panel on top of the small guide rail in the track. If you can’t quite get it in the track, try swinging in from the outside as the outside track wall may be shorter.

You want to put the pet door in your track before applying any weather-stripping to ensure it fits! If it fits well, move on to the next step. See our tips at the end of these steps if you have trouble!

Step 6: Once you’re sure the panel fits, remove the panel from the frame and lay it on its side on the ground. Apply the foam weather-stripping by peeling back the paper and exposing the adhesive. Unroll it along the edge of the panel, pressing to ensure it adheres. Install on both sides, trim to fit with scissors. 

Step 7: The center post weather seal strip (draft stopper) should be installed on the inside of the home. It can install on either the back edge of the sliding door panel or the leading edge of the stationary panel. This strip prevents air leaking between the sliding glass door and the stationary panel. Trim with scissors as needed. Clean the edge of your patio door with rubbing alcohol before installing to assure a good seal.




The Endura Flap Pet Door

The Thermo Panel 3e Patio Panel Pet Door

Removing Side Magnets

How to Adjust Your Endura Flap Magnet Strength

Adjusting the Step Over Height


Which flap size should I get?

Here is a measurement guide to help you out.

What do I measure?

You would need to measure from the deepest part in the bottom track to the deepest part up inside the top track. Also the panel is 1" in thickness so make sure that your track is at least that wide to be able to accept the panel.

What is the step-over?

That is how far from the bottom of the doggy door the flap actually starts. So it is what your pet would have to comfortably clear in order to get out and in.

Is this dog door insert going to provide good insulation?

These are excellent for insulation as they have dual pane Low-E glass, and the Endura flap pet door which happens to be one of the best sealing and energy-efficient doors on the market.

Can I install this myself?

This is a good door for DIY home installations. Its user-adjustable design allows it to have an easy installation process. In the taller heights, it can be a bit tricky since the panel is larger and heavier, so it is helpful to have an extra set of hands. I would suggest taking a look at the videos tab for a better idea of just what the installation looks like.

Can I lock the doggie door?

Yep! We include a well-made closing cover that you slide in place. The tracks are located inside so you don't have to go outside in bad weather to close it off.

How do I lock the sliding door for security?

We include a clamp lock for panels under 80.25". You can also use a Charley bar or the old dowel in the track method. All of these different mechanisms work off the same principle that when in place at the window jamb, will prevent the sliding door from being pulled away from the pet door panel.

Can the patio pet door panel be taken out from the outside?

No, the panel is held in at the top with a spring loaded adjustment piece. Once the thumb screws, located on the inside, are tightened you can't slide down that piece in order to remove it.

What is the panel made of?

The framing is a heavy gauge aluminum.

Can I get this with a flap door that keeps other animals out?

We do have the Thermo Panel 2e panels, but the largest flap is on 7" x 7" in Pet Door version. So it is recommend more for cats and pretty small dogs.

How long do these take?

Being that they are custom and we have to special order the glass, it can take roughly 4 weeks for delivery.

I live in a mobile home with a shorter than normal sliding glass door. Can I get a custom thermo panel?

Yes, you can order a Thermo Panel to accommodate your shorter door. When choosing the Track Height Adjustment Range, select "cust ht under 74 3/4" and then you will be prompted to enter your track height. We will build a panel to your specifications.

I ordered my door but the door frame is too short for my window. What do I do?

You can order a height extension panel from Endura Flap Pet Products that will fit into your door track and add extra height to your Thermo Panel.

Where can I purchase a replacement flap for this door?

You can purchase a replacement flap for small to extra large door sizes. You can see our full list of replacement parts and accessories for other brands like Ideal Pet Supplies and Petsafe here.


Endura Flap products have a lifetime warranty against defects in materials and workmanship under standard regular use. Damage caused by not using the product as intended, improper installation, and chewing is not covered under this warranty.

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