DIYbanter - View Single Post - 40 gal just not enough: Replacing water heater for 2400 sq home. Family of 2 adults + 2 children

Wayne Whitney

On 2008-04-09, wrote:

note it appears in homes that use more water, the typical 2 adults and
2 teenagers savings are less, probably because the standard tank
spends more time heating water and less time standing by. this is a
new wrinkle on the tank vs tankless discussion

Actually, it doesn't say the savings are less, it says the efficiency
improvement is less. Standby losses are basically independent of
usage. The greater the usage, the smaller the fraction of total costs
attributable to standby losses.

So if you are trying to calculate a payback period, and if the
incremental efficiency of the tank and tankless are the same, then
usage doesn't matter. All you need to do is figure out how much more
expensive the tankless is, and how your savings from standby losses
are.

Cheers, Wayne