A 9 KW tankless HWH manufacturer claims that it is sufficient for a
whole house at up to 3 GPM.
A 30 gal short tank HWH is about 30" tall and many are mounted over a
clothes dryer on a shelf.
That got me to thinking:
Size - not too important if hung.
Power - both 9 KW.
Instant hot water: - Tank water is preheated. The tankless requires
0.5 GPM to begin heating.
Cost - Conventional HWH is cheaper.
Longevity - Tankless is supposed to last twice as long.
Replacement elements - Conventional elements about $15 at Home Depot,
Tankless elements are not standard
and cost more.
Recovery - With 9 KW of heating available in both units they may be
(You must use up all the 30 gallons before additional
HW is needed.)
Upgrading: Conventional elements are available in 5, 5.5, and 6 KW
Therefore a 12 KW 30 gallon is doable and it would
Efficiency: Tankless is slightly more efficient.
Location - I am in Florida where the input temperature is 70*F.