We have a oil-fired boiler that generates both the hot water and the heat for the house. My wife is opening a daycare, and per state regulations, we need to have the hot water at the tap be 120 degrees or less. While I'm sure it's possible to regulate the temp of the entire system, I can see problems with simply turning the whole thing down. (e.g. 20 below zero nights)
So, I'm thinking there must be some kind of valve that does this sorta thing automagically. Turns out, I'm right - I did a little research, and lo and behold, I found "Thermostatic Mixing Valves". The perfect thing for my application!
Then, I saw the price - they're pretty dear! The cheapest I could find was right around $100, which seems exorbitant for what it is. Which got me to thinking - why can't I simply throw in a couple of check valves, and a ball valve that controls how much cold gets mixed with the hot? The sum total of the parts would be about 20 bucks. What am I missing here?