Is it normal for an ElectriQ unit to leave a mark on the wall?

That vertical streak is almost certainly a **condensate leak** rather than anything to do with the R290 refrigerant itself. When you bundle the excess copper and cabling behind the internal unit, you often end up creating a "trap" in the flexible drain line or putting pressure on the plastic drip tray. If that drain hose doesn't have a constant downward slope from the moment it leaves the internal gutter, water will back up and eventually overflow behind the casing, running down your wallpaper.

The fact that it's on the right-hand side is a big clue. Most of these units have the drain connection on the right by default, though it can be swapped. If you’ve shoved several meters of coiled pipe back there, you've likely nudged the flexible hose or created a high spot. Even a tiny "u-bend" in that soft plastic hose will stop the flow becuase there's no pressure behind it—it's just gravity doing the work. You might not need to pull the whole thing off the wall just yet. Try popping the bottom clips of the indoor unit away from the wall bracket—most have two plastic tabs at the bottom you can pull down. You can ussually prop the bottom of the unit out a few inches with a block of wood to get a look at the drain connection. Check if there is standing water in the tray or if the hose connection feels wet to the touch.

Also, check your 65mm hole with a spirit level. If that hole is perfectly flat or sloping slightly back towards the room, you’re always going to have issues when the humidity is high. It needs a clear **downward pitch** to the outside. If the bulk of the pipes is forcing the unit to tilt forward even a fraction, the water can miss the internal channel entirely and just weep down the wall. It’s a common DIY headache, but usually solvable without a full teardown.

Spot on about the drain slope. I've seen this a dozen times with those DIY kits where people try to hide the slack behind the unit. One thing people often overlook is the insulation tape around the joint where the internal unit pipes meet the extension lines. If you've bunched everthing up and left even a tiny bit of the brass nut or the copper exposed, that cold metal will sweat like crazy in this humidity. That moisture has nowhere to go but down the back of your wall. Give that connection a feel while you've got the unit propped out; if it's soaking wet, you just need some more insulation wrap.

I'm actually planning to buy this exact unit soon but all this talk about leaks is making me nervous. Does having the bungalow doors open like the OP mentioned actually cause the unit to pull in way more moisture than it can handle? I don't know much about the physics of it, but maybe that's why it's overflowing?

Also, is there a specific trick to clicking those bottom tabs out? I'd be so scared of snapping the plastic and ruining the whole thing on day one.

You shoud verify that the bundled cabling isn't exerting lateral pressure on the polystyrene condensate tray itself, as these budget-oriented ElectriQ chassis are notoriously prone to structural deformation wich causes the tray's perimeter to fail. Furthermore, ensure that the insulation surrounding the refrigerant line connections is hermetically sealed, beacuse any ingress of moist air from your open bungalow doors will imediately reach the dew point upon contact with the sub-cooled brass flare nuts, resulting in localized condensation that bypasses the drainage system entirely. Regarding those tabs, you typically need to apply a firm, upward-then-outward pressure to disengage the latches from the wall plate without snapping the somewhat brittle clips.