How to make your own insulated portable air conditioner window vent seal

  • Post category:DIY
  • Post last modified:June 6, 2021
  • Post comments:11 Comments
  • Reading time:8 mins read

A lot of us can relate to that feeling right in the middle of a heatwave when we ponder for the 40th time – is today the day we order a portable air conditioner.

What if the temperature drops tomorrow and we end up with a not so clever investment adding to the myriad of clutter already in the house.

Then you decide to bite the bullet anyway – UK summers are getting warmer after all – and suddenly the prospect of researching the best portable air conditioner dawns on you. Where do you even start?! 

Well this was exactly our experience this summer when, having a new baby in the house, we finally started looking at portable air conditioners.

We found that most portable air conditioners seem to need a hot air exhaust vent usually via a window in the room.

One option is to simply buy a fabric seal/attachment that goes on the window frame. They cost between £12 – £20 and use adhesive fasteners (commonly known as velcro or hook and loop fastening) to attach to the window frame.

Current window seal for airConditioner not so sturdy and low level of insulation
Traditional window seal for portable air conditioner

However, we weren’t sure about the insulating properties and they seemed very fiddly too. 

Our idea for a portable air conditioner window seal:

We wanted something with higher insulation properties that can also act as a heat reflector while blocking some sunlight too. Our window faces south west so in summer, the room heats up like an oven from direct sunlight before the clock even hits 10am! 

We also ordered the portable air conditioner with next day delivery service so didn’t have time to order a window seal too. The vent attachment that came with the portable air conditioner was only suitable for sliding windows.

Facing this challenge, we needed a quick DIY fix, as we always do.

Our plan and diagram of window seal:

We had some leftover large polystyrene sheets from some furniture packaging. We also had some insulation foil lying around from a previous DIY project. So the rest just fell into place quite quickly. 

A rough illustration of the DIY window seal (not to scale)

Method of making an insulated window seal:

List of materials and tools:

2 cm thick polystyrene sheet x 1
Insulation foil
50mm wide duct tape (adhesive cloth tape)
Utility knife

Step 1: Cut the polystyrene to size

I cut the 2cm thick polystyrene sheet roughly 1 inch wider on all sides than the double glazed glass pane. This will then be attached to the window frame using hook and loop adhesive straps from the inside.

Step 2: Strengthen the edges with cloth / duct tape

Then I used 50mm wide duct tape to strengthen the edges and added a few more lines of duct tape across the whole sheet to strengthen it further as polystyrene can break quite easily. 


Step 3: Cut a hole on the board for the vent pipe exit

I held the flexible vent pipe on the exact position where I needed the cut out hole to be (as a template) and used a pen to mark the position. I then used a utility knife to cut out the perfect circle. Again, I taped the inside of the cut out with duct tape to add strength and stop the polystyrene chipping away.


Step 4: Add insulation foil for better insulation

I then added 2 pieces of insulation foil on both sides of the polystyrene panel secured with duct tape. The insulation foil on the outside will act as an effective heat reflector. By this point, the panel was starting to come together and felt quite sturdy too. It was now ready to attach to the window.


Step 5: Attach the insulated window seal panel onto the window frame:

I used hook and loop adhesive fasteners (like Velcro) so I can remove it in winter, store it away and then next summer, I can simply re-attach it easily.

I used 6 x 15cm long strips evenly spread around the edges and it seemed to hold up quite nicely for the rest of the summer. 


Total build time for the DIY window seal:

I started this small project after work and it took me just under 1.5 hours. 

I hope you find this post useful. Here’s to more comfortable heatwaves in future! Please feel free to get in touch if you have any questions or suggestions. Thanks and speak soon!

DIY window seal build video

Here’s a video of the build process. As mentioned earlier, I built this after finishing my day job around at around 6:30 pm in the evening so apologies in advance if it is a bit dark.

Please like and subscribe to our Youtube channel if you find this video useful 🙂

Tools and Materials:

Here’s a list of tools and materials we used.

Duct Tape
Insulation foil
Polystyrene sheets (reused from furniture packaging)
Velcro/hook and loop fasteners

Any suggestions, or questions, please feel free to leave a comment and I can get back to you as soon as I can.

Thanks again for all your support and readership to date. Much appreciated!

This Post Has 11 Comments

  1. Dan

    I did it!

    I made one and it is amazing. I didn’t have any spare polystyrene so bought a sheet from a DIY store… but I have just finished and it works a treat.

    My bedroom is covered in little polystyrene balls.

    1. Aah did you! very pleased to hear and yes its a right old mess these polystyrene sheets. Glad to know it works. Do send a pic or two if you like and we can upload on here for others to see 🙂
      Thanks for stopping by.

      1. Mark

        I came here after constructing my own version. I used a hobbycraft a1 foam board window (£4), this avoids the mess from bare polystyrene, and cuts down the build time to around 15 mins. Same concept as your excellent description. Cut the board to a little bigger than the upper window size, used vecro on the board and window to fix in place and remove. My heat pipe came with an plastic end fitting, which I set into the foam board and then fixed in place to a cut to size hole with sealant. I can quickly attach the whole heat extract pipe and window cover in a couple of minutes and remove in the same – perfect for the changeable weather on this fair island.

        1. Foam board is a fantastic alternative 👏👍 fixing the plastic end with sealant is a great idea too! Send us a picture if you can and I can put it up on here for reference for others. Well done again and thanks for sharing!

  2. Derek

    Briliant – I was pondering similar using old Secondary Double glazing ABS plastic sheets from the old wooden windows days. This looks much easier compared to cutting ABS to size and an accompanying 150mm hole. Great stuff, thanks!

    1. Aah that would have been a solid build too with the ABS plastic sheets, never really crossed my mind! Glad you found this useful, thanks for stopping by and if you do build one, send through pictures and we can upload for others on here if you like 😉 Thanks!

  3. Samantha

    Hi, this looks so good! Any idea on how to do it for a window that opens inward, I’m assuming your window opens outward right?

    1. Can’t think of a solution off the top of my head for an inward opening window I am afraid. You may have to go for the fabric window seals that are available online. Aren’t there any windows at all in the room that open outwards? Only solution I can think of is perhaps sticking insulation foil to the edges of the window and leave it semi open, and a hole for the exhaust pipe on the insulation foil. It may be too flimsy. Let us know how you get on though! Thanks for stopping by

  4. Jenny Lee

    Thank you so much for the tutorial! I ordered all the supplies (velcro tape, insulation foam, duct tape) from Amazon, and completed the project in about 2 hours. I have jalousies so it took me a bit longer trying to fit the vent in the window, but installing the insulation foam was so easy!


      Great to hear you found this article useful 😊 your project sounds complex with the jalousie!! It would be great if you can send a picture through and I can upload on here for anyone who may be in a similar situation. Thanks again for stopping by and all the best!! 😀

  5. Isabella

    Do you reckon this could work for an inward opening door? Leave door open and fill doorway top to bottom with plywood or some such. Going into an Australian summer here?

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