Main and secondary hot water tanks (Temperature)

Bayview

I have a 65 gallon electric water tank feeding the house. I have an 80 gallon water tank that is heated by the gas boiler which feeds this primary electric tank. The boiler also warms the house. In addition there is a recirculating pump to keep hot water in the far reaches (sinks/showers) of the home. For best function and economy what temperture should I have the 80 gallon boiler heated tank set at to feed the electric tank? Right now when the tanks drops to 110 F the boiler heats the water in the tank to118 to feed the electric tank.

Jamie Hall

That's a bit low. Not for thermal efficiency, but for bacterial growth. I'd want to keep the 80 gallon at at least 130 and preferably 140. Likewise the electric.

Bayview

Thanks for the suggestion on water tank temperature settings. If these tanks are set at 140 F do we risk a kid scalding themselves when washing or showering?

JakeCK

Run them at 140 and install a tempering valve between the hot and cold. 

It also has the benefit on increasing how much hot water you have available to use. If you're really worried about efficiency wrap the electric tank in one of those water heater blankets. The boiler tank helps to satisfy the heating demands of the house as long as it is in a heated space.

JakeCK

Also how do you handle the offseason for the boiler? Is all that water just chilling in there all summer long or do you run the boiler all year?

hot_rod

plumbing codes state temperature not to exceed 120F, delivered to residential fixtures, so install a good ASSE 1017 listed mixing valve at the final tank. Run that tank at 140f or more for the mixing valve to operate properly
A Caleffi Tank Mixer is one of the best valves 😉

Bayview

Thank you all for the suggestions. As to one of the questions, in the summer I bypass the boiler heated tank and drain it of the fresh water and just use the electic tank until October comes around.

JakeCK

Bayview said:

Thank you all for the suggestions. As to one of the questions, in the summer I bypass the boiler heated tank and drain it of the fresh water and just use the electic tank until October comes around.

Good, I was gonna say that sounds like it could be real bad quick. Personally if it were me I would sanitize it like I sanitize the plumbing system in my rv at the beginning of the season.