Parametric Midea PortaSplit Window Adapter

I originally built this window frame pass-through for my Midea PortaSplit and an old Finstral System 500 frame — and I've now been using it for two summers in a row.

The PortaSplit uses a slim hose bundle between the indoor and outdoor unit. Much better efficiency — but there's a catch: the outdoor unit can't be detached because the refrigerant line is permanently connected. It has to go outside, which means the window stays open all summer. Bad for cooling performance, bad for noise, and facing the street it's basically an open invitation.

This insert fixes exactly that: the hose bundle runs cleanly through the frame, the window stays fully closable and engages the original locking mechanism as normal. Cooling with a closed, locked window — the way it should be.

🧩 Modular System

The design follows a simple 3-part concept:

• Base Insert — permanently mounted in the frame, secured with screws or silicone.
• Summer Insert — two-part adapter that guides the hose bundle cleanly through the opening and holds it securely in position.
• Winter Cover — a blanking plate that seals the opening when the unit is stored away. Surprisingly airtight — at least as airtight as an old building allows.

🖨️ Parametric Generator in the Browser

The original model was built specifically for my window profile — which means it probably doesn't fit much else. That's why there's now a parametric generator as a Streamlit web app: enter your measurements, check the preview, and generate matching 3D-printable parts. Runs directly in the browser, no CAD software, no local installation required.

👉 custom-window-adapter-for-ac.streamlit.app

Still a work in progress — but probably faster than trying to manually adapt my very specific window profile to yours. Feedback is very welcome, especially whether the measurement points are clear and where you get stuck during configuration.

More about the idea behind the project and how the generator was built: www-f-l-k.com

⚠️ Note on Hose Diameter

There appears to be a change within the PortaSplit product line: the hose bundle diameter was revised at some point. The original model available here fits the older, larger diameter. If you have a newer unit, check your measurements and use the generator — it can be adjusted to match the current diameter.

⚠️ Important — Installation

Installation requires cutting a slot into the inner window frame. This typically also cuts through the internal steel reinforcement, which affects the structural integrity of the frame at that point. In my case — installed in the lower sill area — this hasn't been an issue, as that area carries little load and the frame remains fixed in the wall opening. I also secured the insert with two screws into the surrounding masonry.

Do not install in structurally critical areas such as the lintel or side jambs.

📋 Disclaimer — please read

I get it: some people love this, others are horrified by the words "cut into your window frame." Both reactions are fair — this is a permanent, irreversible modification to your window. Two things could theoretically follow from that: a weakened frame structure and, depending on how well the cut is sealed, moisture getting into the frame. Personally, after two summers, I have neither — but that's my experience on my window, not a guarantee for yours.

This also only really makes sense if it's your own property. In a rental, this isn't a project you quietly carry out — it's a conversation with your landlord, and without that conversation I'd clearly advise against it. If you know what you're doing and are comfortable with the modification: go for it. Everyone else: don't. Both are completely valid choices.

❓ FAQ — after two summers of use

Structural problems after cutting?
None so far. The slot does interrupt the steel reinforcement, but in the lower sill area that's been a non-issue in my case. Two extra screws into the masonry provide additional support.

Cold drafts in winter?
No. Unit goes to the basement, blanking plate goes in, opening is sealed. Honestly, the old building itself is the bigger source of drafts.

Why not a proper split AC?
Cost and complexity. A permanent installation would have meant different outdoor unit placement, longer refrigerant lines, and cable runs through several rooms — that adds up quickly and gets invasive fast. The PortaSplit is attractively priced and performs surprisingly well.

Why not just run the hose through the window?
I wanted a permanent summer setup, not something I assemble and disassemble every day. Leaving the window permanently open hurts cooling performance, lets in noise, and facing the street it's a security issue.

Why not a plexiglass or Styrofoam insert?
Those work fine — especially in quiet locations, upper floors, or rentals. My window faces the street, so I wanted noise out and the window fully lockable.

Would you build it again?
Yes. Two summers in and I'm still very happy with the setup.

License & Community

Free for personal use, remixing, and further development — print it, modify it, adapt it to your window. That's exactly what it's there for.

Commercial Availability

Production and distribution is handled by SureParts. If you don't have access to a 3D printer, ready-made versions are available online, e.g. on eBay. I don't run the shop myself.