Can you extend a portable AC exhaust hose?

🗓 Updated July 17, 2026 · EcoBack editorial team

The exhaust hose that ships with a portable air conditioner is usually just 1.5 metres long — and the nearest window is rarely that close. So can you simply add a second hose? You can, but the hose length is not an arbitrary choice: it's part of the machine's design. Here's what an extension really costs you, how to do it with minimal loss, and when it's the wrong fix entirely.

Why the stock hose is so short

A portable AC pushes hot air out through the hose with a fan that's sized for exactly the resistance of the hose in the box — typically 1.5 m at 130 or 150 mm diameter. Manufacturers keep it short on purpose, for two reasons:

• Back-pressure. Every metre of hose and every bend adds air resistance. The exhaust fan then moves less hot air per minute, heat backs up inside the unit, and the compressor runs hotter and longer for the same cooling result.
• Heat radiation. The hose surface reaches roughly 50–60°C in operation. It's effectively a heating pipe running through the room you're trying to cool — and the longer it is, the bigger that radiator gets.

That's why manufacturers typically approve only the hose length supplied in the box. It can even be warranty-relevant: some manufacturers like De'Longhi warn in their documentation that extending or replacing the exhaust hose can void the warranty. Check your manual before you buy anything.

If you extend: the 4 rules that limit the damage

• Keep the total run to about 2 m. Going from 1.5 m to 2 m is usually tolerable; doubling to 3 m is where owners commonly report clearly weaker cooling and much longer compressor cycles. Shorter is always better.
• Match the diameter exactly. Measure your hose end — 130 mm and 150 mm are the common sizes. An extension with the same diameter keeps resistance low; any step down acts like a thumb over a garden hose.
• Run it straight and smooth. One gentle curve is fine. Every tight 90° bend costs roughly as much as an extra metre of hose. Support the hose so it can't sag into loops where hot air stalls.
• Insulate it. A fitted insulating sleeve over the hose cuts the heat it radiates back into the room — this single cheap step helps more than most people think, and on a longer hose it's close to mandatory.

Ready-made extension kits with a proper coupling piece exist for both common diameters and cost around €20–35 — a far better bet than improvising.

What doesn't work

• Duct-taping two hoses together. The joint leaks hot air at exactly the hottest point, the tape lets go as the hose warms and flexes, and the unsupported middle sags into an S-curve that strangles airflow. This is the most common DIY failure.
• Narrowing the diameter. Adapting a 150 mm hose down to 100 mm ducting (because a smaller wall pass-through looks neater) chokes the exhaust fan badly. Cooling collapses and the unit may cut out on its overheat protection.
• Very long runs to "hide" the unit. Routing 4–5 m of hose to park the AC in a hallway or closet fails twice: massive back-pressure, plus several metres of 50–60°C hose heating the space. Portable ACs are designed to sit near the opening.
• Extending the hose horizontally out of a wide-open window. If the window is simply open around the hose, hot outside air and your own exhaust flow straight back in — the extension isn't the problem, the unsealed opening is.

Alternatives that usually beat extending

Before you buy an extension, check whether one of these solves the real problem — a unit that's too far from the window:

• Move the unit closer. Sounds trivial, but a portable AC doesn't have to sit where it looks best. Two metres closer to the window beats two metres of extra hose every time — the cold air will mix into the room either way, especially with a fan helping.
• Seal the window instead. Often the hose reaches, but the window can't close around it. A window seal kit (fabric with a zip, ~€15–25) fixes that for tilt-and-turn windows without any extra hose — see our guide to portable ACs in tilt-and-turn windows, or the skylight and roof window version if your only opening is in the roof.
• Pick a split-style unit if the window is genuinely far. The Midea PortaSplit takes a different approach: a slim refrigerant line to a small outdoor unit instead of a fat hot-air hose, so the indoor part can stand several metres from the window without the usual hose losses. It's widely cited in public tests as the standout in this niche.

Note: we haven't tested these units ourselves — we summarise public test results and user feedback.

Frequently asked questions

Can you extend a portable air conditioner hose?
Yes, within limits. Keep the total run to about 2 metres, use the same diameter as the original hose (usually 130 or 150 mm), run it as straight and smooth as possible, and insulate it. Go much beyond that and cooling drops noticeably while back-pressure on the compressor rises. Some manufacturers like De'Longhi warn that extensions can void the warranty, so check your manual first.

Does a longer exhaust hose reduce cooling?
Yes, in two ways. A longer run adds air resistance, so the unit moves less hot air out and works harder for the same result. And the hose surface itself gets 50–60°C hot and radiates part of that heat straight back into the room — the longer the hose, the bigger that radiator. Each extra metre and each tight bend costs a real share of the rated cooling power.

Should I insulate the exhaust hose?
Yes — it helps more than most people expect, extended or not. The exhaust hose carries 50–60°C air and acts like a heating pipe running through the room you are trying to cool. A fitted insulating sleeve (or temporarily a reflective blanket) cuts that heat leak sharply, and on a longer hose insulation is close to mandatory because there is more hot surface area.