Many prefer these old-style top mount heaters. They seem to last forever with a little maintenance.
T° =temperature difference between the desired water temperature and room temperature
T°
Gallon
5
10
20
30
40
55
75
90
120
10° F
watts
45
53
80
93
107
127
147
160
180
20° F
106
187
213
253
293
320
360
30° F
135
240
280
380
440
480
540
