Some of our customers want to know if an acrylic enclosure will melt given it will get hot inside with the 3D printer running.
We have run our enclosed Prusa MK3 printers for ABS 24/7, printing at a head temperature of 255C and a bed temp of 115C, (close to the max the printer can go) for over two years now and the acrylic has not warped.
If you want to talk numbers, the highest internal air temps we've seen with Prusas is 45C if you seal up the fan opening, while acrylic is rated to 80C. The E3D hot end on the Prusa is only rated to work environments up to 40C, although you can push it a little to 45C. After that, the heat sink can no longer keep the filament cool and the hot end clogs. If the air inside the enclosure got anywhere near the point that acrylic would melt the printer would have stopped working.
This also applies to the other enclosures we sell, which all have fans that ensure an optimal consistent internal temperature. This article explains some background on printing with different temperatures for different materials. Even if you closed off the fan hole and other ports and ran your printer at the highest temperatures, the internal temperature of the air inside the enclosure wouldn't get hot enough to warp the acrylic.
https://www.3dupfitters.com/blogs/news/managing-temperature-in-a-passive-3d-printer-enclosure
Issues which can negatively affect longevity:
1. Particles that used to go into the air you breathe will coat the inside of the enclosure over time and will need to be wiped off. Do NOT use glass cleaner or soap, just water.
2. In general, the enclosures are not designed to hold heavy objects on top. All enclosures that need top mounted spool holders are reinforced with a support beam, but placing very heavy objects on the top will cause it to sag over time.