tankless with 40gal tank backup

[slojak]

Hi guys
Got a quick question that has been probably asked a million times. I did a little searching and did not find my topic but just a little so if its out there please just refer me to the post. here goes.

i am a HVAC guy and a bit of an old timer so i have skills in plumbing also.
In my own house i put in a tankess water heater but i wanted to use my old 40 gal. tank for back up. i piped the tankless in parrallel to the tank and put in isolation valves. i kind of forgot about that i have water sitting in the tank. just sitting there for about a year now. is that dangerous? can like the water go bad? i know standing water forms all kinds of bacteria.

so i put the tank in service and ran about 100 gals through it. it smelled a little at first but went away. so what do u think? is this ok?

 

[havasu]

I'm sure it would be fine, but if you want to really sanitize it, you could always add a 1/2 teaspoon per gallon of household bleach into the tank, and then flush it all out one more time.

 

[slojak]

good
have you ever heard of anyone getting sick from the water sitting like that?

 

[havasu]

Depends if the original water was treated or well water. I'd add some bleach and after a quick flush, you won't have any further worries.

 

[DCPlumber]

Slojak,

Have you considered piping the water heaters in series, putting the old one first to use as a tempering tank (don't even turn the electricity on), which could help reduce the heating load on the tankless, then if the tankless fails to heat, just turn on the breaker to the old one so you aren't without hot water but for a short time.

Just a thought.