a lady brought in a wild baby rabbit her cat had rescued
i took it off her and said i would wrap it up and keep it warm
she asked if i would put it in an incubator
i said no i would wrap it in pastry and put it in the oven
her face looked like this
each bubble of air as it rises carries water on its surface,
the movement of the water creates current
the more bubbles the more moving water
this is how air powered UGF work
+1 to what suphew said
especially in a small volume, i have run for a few years with no chiller
but a large volume of water with the sump in a cold basement