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Indirect water heater temperature

I'm planning my indirect install and have a few questions about temp settings for the tank and mixing valve.

I purchased a Taco 5003-C3-G to install. The water heater is an HTP Superstor ultra 45.

My plan was to set the aquastat on the HTP to 140 and the mixing valve output at 120.

After reading the specs on the Taco, I see the minimum differential appears to be 27 degrees. A bit more than I had planned.

Technical Specifications:
Connection: 3/4" Union Sweat
Maximum Flow: 20 GPM (76 L/Min)
Minimum Flow: 1 GPM (3.8 L/Min)
Hot Supply Temperature: 120-180°F (49-82°C)
Cold Supply Temperature: 39-80°F (5-27°C)
Maximum Inlet Pressure: 230 psi (15.85 Bar)
Maximum Variation in Supply Pressure: 20%
Minumum Temperature Differention Between Hot Supply and Mixed: : 27°F (15 °C)
Outled Temperature Range: 85-175°F (29-80°C)
Factory Set To (115-120°F (41-45°C)
Accuracy of Outlet Temperature: ±3°F.
Related products

(It seems Taco could have spell/grammar checked their documentation a bit better!)

Is this the best mixing valve to use? Maybe another make/model would be better? Any suggestions?



  • hot_rod
    hot_rod Member Posts: 22,246
    The Caleffi 520 has a tighter spec, it is also a fast responding valve, intended for tankless coils and tankless heaters. It is also a 100% shutoff should you lose cold supply. There are two different body sizes, depending on your desired flow. The standard 3/4 body is a bit lower Cv.


    A valve with a wider temperature spec will still mix accurately, but they tend to “hunt” if you fall below the spec. So water will be exact, fall a bit, overshoot a bit, it’s just the way a wax cartridge valve works, not brand specific.

    The max flow on that valve would be problematic also, extremely high velocity with 20 gpm in 3/4 copper tube for example
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Rickoo
    Rickoo Member Posts: 54
    Thanks Bob, that looks like a better mixing valve for my application!