Work out mixing valve temperature instantly with clear inputs, formula shown and shareable results.
A thermostatic mixing valve is a simple energy balance: the fraction of hot water needed is the gap between target and cold divided by the gap between hot and cold. That fraction, multiplied by the blended flow, gives the hot demand the cylinder and hot water pipe must actually deliver.
Hot fraction
Hot fraction = (target - cold) / (hot - cold)
Flows
Hot GPM = total x hot fraction; cold GPM = total - hot GPM
Preliminary estimate only. Scald protection settings and valve selection must comply with local plumbing code and the valve manufacturer's instructions.
Hot fraction = (target - cold) / (hot - cold). A thermostatic mixing valve is a simple energy balance: the fraction of hot water needed is the gap between target and cold divided by the gap between hot and cold.
Storing at a higher temperature and blending down means each stored litre serves more than a litre at the tap, so the effective draw-off is larger than the cylinder volume.
This calculator takes 4 inputs: Hot supply temperature, Cold supply temperature, Target blended temperature, Total blended flow. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.