Heating & hot water
Mixed-water temperature
- where
- mixed temperature (°C)
- hot flow (L/min)
- hot temperature (°C)
- cold flow (L/min)
- cold temperature (°C)
Explain this equation
Works out the temperature you get when hot and cold water streams are mixed. Use it to predict an outlet temperature from the hot and cold flows at a tap or mixer.
q_h and q_c are the hot and cold flows. T_h and T_c are their temperatures. T_m is the mixed result.
The heat in the mix equals the heat brought in by each stream. Since both streams are water with the same density and specific heat, these cancel, leaving a flow-weighted average of the two temperatures.
Sense check: 6 L/min at 60 °C with 4 L/min at 10 °C gives 40 °C. Equal flows give the midpoint.
Watch out: this assumes no heat losses. It does not check a thermostatic mixing valve or scald protection.
Enter your values to see the result.
Good to know
Assumes equal density and heat capacity, no losses. Does not verify a thermostatic mixing valve or scald protection.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.