Temperature Differential

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What is temperature differential?

Temperature differential is the difference between the hot water supply temperature and the outlet temperature from the mixing valve.

Even the technical departments of some of the countries best known shower mixer manufacturers get the answer to this question wrong.  They will often quote that their mixing valves will produce a stable temperature + or minus 1°C.  This is not the temperature differential but outlet temperature guarantee.

Why is temperature differential important?

In a perfect world hot water supply temperature would be 60°C at the outlet but in the real world hot water supply temperature at the outlet can be as little as 42°C.  This means that if the user selects a temperature of 43°C on the mixing valve the resultant 1°C difference in supply and outlet temperature will mean that only a small amount of cold water will be required to be added to the hot supply.  This results in many thermostatic cartridges reacting as if the cold supply had failed and as such shut down the mixing valve or at the very least de stabilize as it tries to compensate.  Due to this performance limitation many mixing valves have a temperature differential of 10°C.  In real terms this means that the hot water supply temperature must be a minimum of 10°C hotter than the set out let temperature for the mixer to function properly i.e. Mixer set at Outlet temp 43°C will require a hot water supply at minimum temp of 53°C.

What effect will this have on my mixing valve?

If the temperature differential is under 10°C the mixing valve will de stabilize i.e. will shift dramatically between hot and cold as it tries to compensate for the low flow of cold supply.  In some cases it may shut off completely or in extreme conditions there may be a risk of scalding.

What is a standard temperature differential?

The vast majority of manufacturers quote a minimum temperature differential of 10°C with many being in excess of that.  The higher the temperature differential the more likely the unit is to destabilize and the higher likelihood of a scalding incident.  The lower the temperature differential the more stable and safer the mixer is.

What is the temperature differential of FM mattsson units?

FM Mattsson thermostatic and pressure balanced mixing valves due to their unique technical advantage have a temperature differential of 0°C.  This means that if the hot water temperature is 42°C than the outlet temperature can be set at 42°C and still maintain a constant stable temperature and flow.  In real terms FM Mattsson mixing valves can be relied upon to perform at 100% over the broadest range of conditions out performing any mixer currently available.

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