It depends on how you are intending to use vacuum.
Subjecting the whole Findenser unit to vacuum (e.g. placing it in a vacuum drying oven)
You should not do this – it could damage the Findenser seals.
Pulling a vacuum through the inner glass body of the Findenser before use
You can do this, for instance to dry the inside of the Findenser, or to remove air to replace with inert gas before an experiment.
As the inner glass body is an open tube, the vacuum level achieved would depend on how you had it connected up (e.g. whether you made a good seal at each end, and which vacuum pump you used).
Pulling a vacuum through the inner glass body of the Findenser during use; use as a rotary evaporator condenser
This is not recommended.
In rotary evaporators, vacuum is used to reduce the boiling point of the solvent, e.g. to 40°C. This would therefore reduce the temperature difference (delta T) between the chemical vapour temperature and ambient (air) temperature – and a good delta T is required for heat to effectively be dissipated out from Findenser. Findenser would therefore not perform well, so is not suitable for this type of application.
Furthermore, if you ran an experiment while you drew a vacuum up through the Findenser and out of the top, you would be pulling the generated chemical vapours up more quickly through the Findenser, reducing its performance; and if you connected the vacuum to a side arm, the chemical vapours would be drawn directly out the side arm, bypassing the Findenser.
Use of Findenser on the exhaust of a vacuum pump (e.g. of a rotary evaporator)
Findenser works well as a vacuum pump exhaust condenser – see our case study.