I am replacing a 40 gallon tank heater with a tankless unit and would like to know what size unit to put in with the maximum simultaneous use being one shower and washer. I live in virginia. Is there a big fluctuation in temperature when someone suddenly opens a faucet for example?
A constant flow rate for the shower depends upon your existing piping. If you have varying flow in the shower now, you will when you make the change, so a larger feed to the shower and a pressure/temperature balancing shower device would help control the output.