Tempering tanks are a very good idea--however, not with an electric
water heater. Do a search for Legionaires Disease and you'll find that
almost 30% of homes with electric water heaters have Legionella
bacteria growing in their tanks.
The reason electrics have the problem is because they heat from the
side. That leaves a cooler zone at the bottom of the tank. The
bacteria feeds on sediment and cooler water--anything under 122
degrees.
The experts recommend upping electric water heaters to 140 as the only
way to effectively kill the bacteria.
Since gas water heaters heat the water from the bottom, all the heat
goes into the sediment, killing the bacteria.
Here's an excerpt from a scientific study:
Like other authors (3,4), including the World Health Organization
(WHO) who published a recent monograph on the Legionella problem in
drinking water (3), we believe that there is evidence for the
transmission of legionellosis through the drinking water distribution
systems in private homes. This is a serious illness associated with
high death rates (up to 12%). Primary groups at risk (the elderly,
smokers, the immunocompromised and patients suffering from chronic
respiratory illnesses), are groups who include a large proportion of
the population at home. Although we support prevention against tap
water scalds, we are against setting water heater thermostats at 49°C
because we believe this could facilitate proliferation of Legionella
inside the tank and increase the risk of legionellosis.
Domestic water heaters, particularly electric devices, can certainly
be contaminated by Legionella. In Quebec, a study of 211 homes (178
electric water heaters, 33 oil or gas water heaters) found Legionella
contamination in 40% of electric water heaters. No water heaters using
fossil fuels were contaminated (5). The authors concluded that,
because of design variables, use of an electric water heater was the
most significant factor leading to Legionella contamination in hot
water (5) in the home.
Here's the complete link to the study:
http://www.pubmedcentral.nih.gov/art...?artid=2094925
If you want more info, google legionella electric heater
Are we having fun yet?