By understanding the causes of stuck fermentations and how to avoid them, you should never get stuck again.
The batch size for most homebrewers has been around 5 gallons (19 L) for a very long time, and keeping this volume of fermenting beer cool is not difficult. Recently, however, many
Headspace can cause oxidation, especially in secondary fermenters. Anything that is done to eliminate air helps minimize oxidation. And adding de-aerated water can reduce the odds of oxidation, but the process deserves
To answer this question I will assume that you do not have a chilly root cellar where you are fermenting lagers, and that most, if not all, of your homebrews are ales.