The only time you should pipe two water heaters in parallel, is when they
are exactly the same capacity and flow rate. I think you'll find that the
electric water heater is going to cost you a lot more to operate. I also
think that if you turn off the gas supply to the gas water heater, you're
going to be running out of hot water.
Water heaters are rated by their 'recovery rate', or how fast they can raise
the temperature of the water. This is typically a rise of 90 degrees. The
recovery rate of an electric water heater depends on the wattage of the
heating elements. A typical electric water heater with two 4500-watt heating
elements takes about two hours to heat 40 gallons of water. A typical 40
gallon gas water heater takes about one hour to heat 41 gallons of water.


"Craig Robison" wrote in message
. ..
I have a perfectly good 40 gallon Natural Gas water heater (in the attic)
it
sometimes proved to be insufficient with company in town so I did what you
should not do and cranked up the temp to about 145-150 and it seemed to
help
although we still ran out during times of heavy use. Now we have a kid on
the way, water is SCALDING HOT and we are going to need more of it
anyway.
Long story short I found that it was cheaper to add a second 40 gallon
water
heater (plenty of room) than to replace the existing one (I hated the idea
of removing a good water heater, it is only 5 years old). Also, I went
electric instead of gas, mostly because I did not want to cut a hole in
the
roof for the vent AND the electric model was cheaper AND I just happened
to
have a no-longer-used 10 gauge wire running right to it. Natural gas
prices
are sky-rocketing but I still think that a gas water heater is cheaper to
operate than an electric model SO, I plumbed them in series rather than
parallel. That is to say the hot water leaves the gas water heater and
goes
into the electric water heater then into the house. In this manner I
figure
that the gas heater is still doing most of the heating and the electric
one
is more like a storage tank. I have set them both to 125 degrees, the
minimum temperature that the dishwasher manual recommends (to do this I
filled a bucket full from the T&P valve and took the temp right there).
My
question, is there anything wrong with having the water flow from one to
the
other in this manner? I cannot see why the electric water heater cares
what
temperature the inlet water is. For what it is worth the guy at Home
Depot
thought it was brilliant, but he aint a plumber, and neither am I...
Any Thoughts?

Craig