Thermo Sash 3e Cat Doors for Sash Windows


  • Consumer favorite for window pet doors
  • Maintains insulation with dual pane, LoE glass in sturdy aluminum framing
  • Installation is a breeze with no tools required, perfect for renters and vacation homes
  • Built-to-last with 15 year warranty, made in the USA
  • Free shipping within the U.S.

Stock No: C07PPC06

Availability: In stock

Price From: $419
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Price From: $419
Thermo Sash 3e Cat Doors for Sash Windows
"This thermosash product is made to be sturdy and insulating. It is a perfect buffer against rough weather. "

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  • Consumer favorite for window pet doors
  • Maintains insulation with dual pane, LoE glass in sturdy aluminum framing
  • Installation is a breeze with no tools required, perfect for renters and vacation homes
  • Built-to-last with 15 year warranty, made in the USA
  • Free shipping within the U.S.
Flap SizeFlap DimensionHeight to Raise WindowStock No 
Small6" x 11"18 1/2"07PPC06 

Adjustment Ranges

  • 22" - 25" Custom Order (not available for Extra Large)
  • 25" - 28"
  • 28" - 31"
  • 31" - 34"
  • 34" - 37"
  • 37" - 40"
  • 40" - 43"

Pet door has 1" framing, measure your track width to make sure that your window will accomodate the sash.

Final Sales: Adjustment Range 22" - 25" are final sales and cannot be returned. All Extra Large sizes are also custom and non-returnable. Final Sales products are made to order and will take extra time to ship.

Thermo Sash 3e™ Sash Window Cat Door

Our customers find this cat door perfect for their homes. You can finally relax from letting your pet in and out of the house; this product takes care of that. There are no tools needed for insulation, so forget about spending money on contractors. It's easy to install, yet durable, so no matter what the weather is like, your home stays comfortable.


Every Thermo Sash 3e™ includes the award winning Endura Flap™ Door Flap -- the best engineered high performance pet door flap ever made.

The Endura Flap™ is guaranteed for 15 years!

Dual Pane, Insulated Low "E" Glass is the highest performing glass available. It is standard on the Thermo Sash 3e™.

Spring loaded design allows for installation and removal in seconds. No tools required.

Built-In Anti-Whoops allows for 3/4" change in adjustment range to allow for small measuring errors.

Draft Stopper keeps air from coming in between the two windows.

Adjustment Ranges accommodate windows 22" - 43" wide in 3" increments. Be sure your track width is at least 1".

100% designed, engineered, and manufacturered in the USA.

Customer Reviews

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  • very nice review by tay
    5 5 very nice

    works like a charm, measuring was a little difficult to make sure everything was ready to go. It keeps everything well insulated, love the high quality of the glass and flap. It is air tight!

    (Posted on 12/5/2017)

  • Wonderful product review by Patty
    5 5 Wonderful product

    My husband and I are so happy with this cat door! We have two cats that just turned a year old. We let them go outside during the daylight hours when we are home. I was constantly letting them in and out, or leaving the back storm door propped open, letting the flies and neighbor cats in as well. My husband did not want a pet door, but I convinced him to give this one a try since no holes were drilled in walls or doors. I was able to easily install the window by myself following the video instructions, adding some shims (provided) to make everything line up, and also some insulation strips (provided). For training, I took out the side magnets and shoved the bottom magnet to the side as shown in the instructions. One cat used it immediately for treats! For a day and a half, the second cat would only use it when we held the flap open. By the end of the second DAY, they were both using it regularly! After a week, I moved the bottom magnet over so that it worked on the bottom of the flap, and after pushing the flap for them a few times, they were pros. A week and a half later, I put the side magnets in, and they didn't seem to notice any difference! There is no cold air coming in at all now! Or neighbor cats! We have NOT had any problem with the aluminum "sweating" as some reviewers did. I did apply the protective treatment that came with the door. We ordered the white, and it looks nice - much less noticeable in the window than I had thought it might be. I wish I could post a pic! Highly recommend this product!

    (Posted on 11/16/2017)

  • Superb review by Krisa
    5 5 Superb

    Quality exceeded my expectations. Highly recommend.

    (Posted on 5/8/2016)

  • Cats are happy. review by Rally
    5 5 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.

    (Posted on 2/15/2016)

  • excellent pet door review by ally
    5 5 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

    (Posted on 1/19/2016)

  • It's great! review by Lou
    5 5 It's great!

    My cat loves it! She was a feral cat and hates being stuck inside so this gives her easy access to the outside. We are now into single digit temperatures and I have not had any problems with cold air seeping in or around the cat door. It is a bit noisy when she goes in and out but I actually find that reassuring -- let's me keep track of her comings and goings.

    (Posted on 1/8/2016)

  • Nice pet door review by SteveInGb
    5 4 Nice pet door

    This is a nice pet door that works well. The only draw back is that the frame is aluminum and not insulated or thermally broken, which means that if you are in a colder climate and utilize humidifiers, all of the aluminum components will sweat, sometimes a lot, since it will be near the same temperature as the outside air. Think glass of ice water on a hot humid day.

    (Posted on 12/7/2015)

  • Easy to install and attractive review by Windsailor
    5 5 Easy to install and attractive

    Excellent design, well worth the price, so easy to install, attractive.

    (Posted on 7/31/2014)

  • Excellent pet door for windows review by Ken
    5 5 Excellent pet door for windows

    I have used another brand product for 20+ years with flaps that allowed air-conditioned air out and cold air in in the summer. Even when I bought new flaps they did not seal very well at all.
    This product was easy to install, looks good in the window, and seals perfectly. The price is well worth it. I would buy it again in a heartbeat.

    (Posted on 7/29/2014)

  • Excellent Product review by ktwindow
    5 5 Excellent Product

    We ordered the small size door for our cat. My husband installed the window. He did not appear to have any difficulty but he's an engineer. We did need to go get some extra weatherproofing for our window but we have old sash windows and our gap was too wide for the included weatherproofing strip. Not a big deal as we were able to find what we needed at a hardware store. Our cat was used to an old door flap that did not have magnets and she could open with her paws. It did take her some time to adjust as she has to open it with her face. I did put painters tape around the sides over the magnetized area and taped down the bottom piece for about a month- this made it open much easier. We did move her food dish outside to provide additional incentive for her to use it. After a month, we removed the tape and she uses it like a champ. It seals nicely and does not let in a draft.

    (Posted on 1/7/2014)

  • Cats love it! review by Nenz
    5 5 Cats love it!

    This window is great! The magnet is strong and it took awhile for them to get used to it compared to the soft plastic flap doors. It is now winter in the Northeast and the bedroom where this door is does not leak cold air. I used weather stripping provided along with some extra I bought at the store. You probably don't even need the extra stripping, I just wanted to make sure. I am very pleased with the purchase and would definately recommend it to others. Also, they love the window on the side panel!

    (Posted on 12/19/2013)

  • Attractive, functional, highly recommend review by LOVE IT!
    5 5 Attractive, functional, highly recommend

    After purchasing and returning 4 different pet doors, and cutting a hole in an interior wall to find that a major electric wire was blocking the opening… We finally found the Thermo-Sash Pet Door for windows. It matches our window so perfectly, no one notices it. It took a couple of weeks and treats to train our cat, but no more late night meowing to get out or come in! I had no trouble placing it, and it looks great. FYI, I removed a few magnets to enable our cat to more easily open during training. They are easily reinserted.

    (Posted on 11/26/2013)

  • Good Product in Bad Condition review by Wren
    5 4 Good Product in Bad Condition

    The box arrived with a big tear in the side and one of the heavy knobs for securing the door was badly bent. The box was falling apart and the tape was coming loose like it had dried out.
    The return instructions were rather strict....from what I read..They will not accept a damaged package?? They suggest you repackage in fresh materials. This is a big door with lots of Styrofoam etc. As a result I decided to try and use it damaged. It is working fine and does appear to seal and insulate well.

    ed. note - packages with visible damage should be inspected at once. If there is damage to the contents, we will issue a 'damage call tag' immediately, pick up the damaged item and replace the product at no charge to the customer. This applies to any product, not only those we manufacture.

    (Posted on 6/23/2013)

  • Excellent review by Kathy
    5 5 Excellent

    Very satisfied with all aspects of door. Had been wanting a pet door for some time but didn't have a door or wall in which to install so this window version worked great. Installation was quick & easy.

    (Posted on 4/29/2013)

  • Good for cats review by Amy
    5 5 Good for cats

    Good window, easy to install once we got the sides trimmed down 1/4 inch (you'l need a hack saw), The door works great and seals really well. Training the cat took about 2 weeks but once he got the hang of it things were so much easier. no more having to get up and let him in or out all the time or listen to him cry. The only draw back now is he like to bring his "toys" inside on occasion. Sometimes still breathing :~(

    (Posted on 4/27/2013)

  • best door ever! review by bco
    5 5 best door ever!

    I have had three of these doors: the first, installed in the wall of my old house; the second in a human door; the third, the Thermo-sash. These are wonderful doors! They keep snow, wind, and uninvited critters out, but are very easy for pets to use. I have two cats who have never had a problem with the doors. I will continue to purchase these pet doors, as they are far superior to any others I have seen.

    (Posted on 2/15/2013)

  • A quality product that works as advertised review by ChrisR
    5 5 A quality product that works as advertised

    Easy installation and good fit. We were not sure if our smaller 9lb cat would be able to open the flap as the magnets seem quite strong. We ended up putting two layers of masking tap on the bottom bar and that eased things nicely. No problems training our cats to use the flap - holding their favorite toy/treat on the other side quickly overcame any caution.

    (Posted on 2/11/2013)

  • Follow up to a review I posted 10/26 review by KateF
    5 5 Follow up to a review I posted 10/26

    I purchased a Thermo Sash IIIE cat door for sash windows. As I mentioned in my first review, It will pay for itself in one winter with the savings I will realize on my utilitiy bills. However, I also mentioned the sliding security door would not work because of a lip that protrudes on my window. To follow up on this - last weekend I ran that locking pet door through a table saw with a new "general construction" grade blade . The door is now exactly 6 and 7/8ths inches wide. I can now side-load the door, settle it into the bottom rail and then slide it back to center where the lock holds it securely in place. I easy solution if you're the handyman ( or woman ) type! I love my door!

    (Posted on 12/15/2012)

  • Insulated pet door review by Bob
    5 2 Insulated pet door

    Although the flap is innovative and works well, the surround is aluminum and is not insulated at all. In a cold climate, it weeps condensation continuously. It was not a simple fit with our particular vinyl windows that have a small ridge at the bottom of the frame. Also, only one side fits the side of the frame where it fits into the channel. The other side is too big, resulting in a small gap from top to bottom. The weather stripping supplied was in excess of what was needed and it too was only effective in the the solid part. There is no surface to run the weather strip over the area that is adjustable resulting in about 1/5th with no weather stripping. I will probably return it and order just the door and make my own insulated panel that won't look as nice but up hear near Chicago we need something that is actually insulated.

    (Posted on 11/24/2012)

  • Best Investment You'll Ever Make! review by KateF
    5 5 Best Investment You'll Ever Make!

    Gotta admit, when comparing Pacific Patio's prices with doors you can get at various retail outlets, I was a bit leery. However, after replacing my cat door for the third time in as many years, I was in a bit of a huff, Not to mention, with rising heating costs coupled with reduced income - I had to do SOMETHING! I ordered it Sunday night. It was on my doorstep Thursday morning. I had it set up in less than ten minutes. Then another ten minutes to add all the weather stripping that comes with the door. It was REALLY blowing hard the day I installed this door. I had to smile as I watched the curtain over the window. It never moved! Not even a fraction of an inch! This window is THAT weather tight! This window will pay for itself in one winter on the money I will save on my heating bill.

    On the downside - My sash window has a lip the protrudes out about an inch over this new pet door on the inside. Because of that - the locking cover will not slide downward in it's tracks. My fix for this - I took a scrap piece of vinyl siding and trimmed it to fit tight in the tracks. This siding has just enough bend to it, I can squeeze it into place yet it's still stiff enough my cats can't pull it out. I consider this a truely minor inconvenience in the face of this door's outstanding quality. I was looking for weatherproof. I got weatherproof!

    Surprisingly, I sent a feedback email to Pacific Patio letting them know how pleased I was with their product. I mentioned the issue with the locking cover. They assured me - they are aware of the problem and are working diligently on finding a solution.

    Even still - This door is the best investment you will ever make! If you'd care to email me I can send you pictures of mine.

    (Posted on 10/26/2012)

Weight 1.0000
Manufacturer Endura Flap
Your Maximum Pet Size Cats
Manufacturer's Restocking Fee 0

Design of the Endura Flap™



Adjusting Magnet Strength for Training




Leaf Blower Test


Installing the Thermo Sash 3e


Replacing the Flap in the Sash Pet Door


Switching the Flap Side


Installation Instructions for the Thermo Sash 3e Cat Doors for Sash Windows


1x Window pet door

1x Foam Weather Strip

1x Center Post Weather Seal Draft Stopper



1Loosen the thumb screws at the end of the sash. This allows the spring mechanism to move freely side to side.

2. 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 thumbscrews.

If the pet door sits properly, remove the pet door to put on the foam weather-stripping in step 3.

3. 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 the top and the bottom. Trim to fit with scissors.

4. Mount the draft stopper vinyl weather strip. This strip prevents air leaking between the window frame when raised to accommodate the sash. Trim to fit with scissors.



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.



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. 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 thumb screws.Replace the end spacer and screws.



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.



If your window is thicker than 1 inch, your locking cover may hit the overhanging window. If you cannot place the sash flush with the inside track wall, you might not be able to install your thermo sash with the locking cover in place.



You will first need to loosen the thumbscrews, you may first need to lift the pet door up to loosen the bottom screw. Then compress the window pet door and tighten the thumbscrews once again for easy removal.



For help with installation, replacement parts or other questions visit or call 805-781-7700 Monday-Friday 7am-4:30pm PT




Click below to expand:

First raise up your window and check that it can go up far enough to be left with an opening 18 1/2" high. Next measure the width of the track from left to right, including going inside the track on both sides. Last measure how wide the track is that the window slides in (needs to be at least 1")

Track width needs to be at least 1" thick.

It comes standard on the left, if you are looking from the inside of the house. You can switch it to the other side if you need and that only requires a screwdriver.

This is designed to be a fairly simple install that does not require any tools. Take a look at the video under the installation tab to see if it something you would be able to do.

The Thermo Sash 3e has the Endura Flap which is far better in sealing and durability than other models. Dual pane lo-e glass offers superior insulation value. Therefore, the Thermo Sash will be a much more reliable and longer lasting option then the more inexpensive options.

We can, the only thing is that we would not be able to use glass so there would be quite a bit of aluminum and some customers are not happy with the aesthetics. This would also fall under the custom and non-returnable category.

You can by removing some of the magnets. On the videos tab check out the "Adjusting Magnet Strength for Training."

If you've mismeasured, you may be able to fix it. To make your sash cat door about 1" wider, you may purchase a width extension (or make your own using 1" x lumber). To make your window kitty door insert slightly shorter you may trim the side flanges on the spring loaded adjustment piece with a hacksaw or a jigsaw with a metal cutting blade.

Any of the Thermo Sash doors with "Custom" listed means that the door is built to order and therefore it is non-returnable.

We can only do custom widths, not custom heights.

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