Tankless Ng have an Energy Factor of between 82-90+ Sears best Ng tank
is in the 60s. Ng tankless have bottom efficiencies of 82% and Takagi
TH1 is 94%. Few tanks match this. Tankless have no tank to rust out and
can last 30+ years, Tankless Ng have no standby loss. Downside is your
gas supply must be measured with competing apliances on and factor gas
pressure variances in pipe sizing or you may never get 100%., or be sure
your gas is adequate before you purchase one and that you know how much
your pipe instal is. Tankless do not turn on at low flow maybe 1/2 gal
so you may have cold comming out. But the savings I get from a Bosch
117000 btu give me a 4-5 yr payback so it is worth it. If you have kids
the unlimited HW might just cost you more. Im sure a reapair could be
expensive on tankless.