The general rule of thumb is their first week, 90F, then dropping 5F per week after that. So, 90 minus (10 weeks times 5 degrees a week which is 50 degrees) is 40, so I would think 20 is too cold for them, still.
May I ask what is the concern about them inside? Are there odor problems? That can be managed by making some adjustments. Often it is the water.
Take a look at these for ideas.
post number 8 from this