mixing valve or ball valve, or leave it alone
Hello to my favorite forum. I've been reading for months with glee. I have consulted with two plumbers and got different answers to solve my problem. I'd love to hear feedback on this.
I am having put in a gas tankless water (controversial on this board) heater to supply a very large tub in our house (already have LP for the furnaces). Our electric tank heater is 50 gallons but the tub will hold over 75. Even though the tank is new and will recover fast, no one wants to wait for that. Both plumbers agreed that mixing a little hot water from the tank will assist the tankless (mixing BEFORE the cold water enters the tankless heater).. Well water is cold, probably 50 degrees and we want 105 degrees or even a little more (my wife has skin, I don't know how it doesn't burn). One plumber suggested a mixer (25-30$), like one for a boiler. The other suggested just a ball valve, only 12$. Does anyone think this is neccessary? Should the tankless be left to do its own thing and blast 125,000 btu, or does a little mixing help it run at less than max? If it is useful to mix, which valve is better?
Thanks for any feedback on this topic.