On Jun 5, 7:30*pm, BoyntonStu wrote:
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,
etc.
* * * * * * * * * * * * * * * * * *Tankless elements are not standard
and cost more.

Recovery - *With 9 KW of heating available in both units they may be
equal.
* * * * * * * * (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
sizes.
* * * * * * * * * Therefore a 12 KW 30 gallon is doable and it would
heat faster.

Efficiency: *Tankless is slightly more efficient.

Location - *I am in Florida where the input temperature is 70*F.

The tankless output is at a rated voltage probably 240, Your voltage
may be only 220 and go lower during high demand, so take their
published specs with great suspicion. The only way to know is buy one
and hook up garden hoses to test output and test it at the same length
run of what you have to measure temp drop from a long run, I think its
to small a unit. and how cold is incomming water in winter, that
colder water could ruin everything you paid for. Mine is a 117000 Btu
Ng unit, a comparable electric might consume 40,000 watts