HOT water.
In my house, I am re-doing the water heating system and most of the plumbing. I am debating the best way to get really hot water. I want my primary hot water to be 120 degrees. This will feed all the taps, showers, and the back spigot (mixing valve spigots are GREAT!). I want 150 degrees or so to go to all the washing machines and dishwashers. I've got 2 options.
Option 1, have a small tankless water heater to boost the temperature of the hot water for my appliances (30 degree temperature rise won't require a big one).
Option 2 is to have the water heater set to 150 all the time and then use a thermostatic mixing valve to temper the water down to 120 for the taps. A thermostatic mixing valve mixes cold water into hot water to make warm water. It can also extend the capacity of a tank-style water heater because the tank of water is kept at a higher temperature, but less of it is used to make a given volume of tempered water. In my system, the 120 degree tempered water would supply most of the plumbing, but I would install a T fitting to supply un-tempered 150 degree water to my appliances.
My water heating system will be highly efficient, and it will be less expensive to heat water via water heater than via heaters in individual appliances. It will also reduce wear and tear on the appliances by reducing the time spent in a heating delay.
Clear as mud?
Dave