No. PETG's enclosure status in this site's material data is helpful, not required, and that distinction is the whole answer.
An open-frame machine in a normally heated room prints PETG without difficulty. What it does not tolerate well is a draught.
What "helpful" is buying
PETG contracts 0.2 to 0.6% as it cools — more than PLA's 0.2 to 0.5%, much less than ABS's 0.4 to 0.8%. That is enough that a large flat part in a cold or moving airstream can lift a corner, and not enough to require a heated chamber.
So the benefit of an enclosure is draught exclusion and a slightly warmer ambient, not chamber heating. A cardboard box over the printer captures most of it.
The reason not to enclose it fully
Heat. PETG needs some part cooling for overhangs and bridges — less than PLA, but not none — and a sealed enclosure that climbs above roughly 40 °C starts to work against you: overhangs droop, small features lose definition, and stringing gets worse because the plastic stays tacky longer.
If you print PETG in an enclosed machine designed for ABS, leaving the door open is often the better setting.
What actually causes PETG failures
Not ambient temperature. In rough order:
- Moisture, which produces stringing, bubbles and weak layers, and is fixed by 4 to 6 hours at 65 °C
- A first layer squished too hard, which welds the part to the plate and damages the surface on removal
- Nozzle temperature too high, which is the main stringing lever after moisture
- Insufficient retraction tuning, since PETG is stickier and stretchier than PLA at travel temperature
An enclosure fixes none of those, which is why people who buy one for PETG are often disappointed.
When it does become worth it
Large flat parts, a cold workshop, or a machine positioned near a door or window. Those are draught problems, and an enclosure is a good draught solution.
For everything else, spend the money on a dry box instead.
Set the material selector to an open-frame machine and PETG survives the filter while fifteen other materials do not — which is the practical meaning of "helpful" against "required". Where an enclosure genuinely earns its keep is set out in the enclosures guide, and PETG's own numbers are on the PETG page.