I have a "deluxe" shower stall that has dual shower heads on opposite walls. The "primary" shower also has 4 body sprays, while the secondary shower is a hand held device that adjusts up and down. The rough ins had to be 3/4" piping and in order to have adequate water pressure, I removed the water saver devices. Now, I have a flow rate of approximately 8-10 gallons per minute. I tried using a SETS electric tankless water heater (4 element unit, 22KW) as a booster to my 40 gallon tank and also tried the 4 element with another 2 element unit functioning as 2 boosters before the hot water tank. This system was unsuccessful for several reasons. The draw from the electricity was so strong that my lights flickered, the reset buttons on the unit were constantly needing to be reset, and although the water was warmer and never went "cold", it was not "hot" water. I have been told that with my setup, I need to look at a tankless water heater that operates off of gas. Bosch was recommended, but their unit only gives a 50 degree rise off of a 5 gallon flow rate. Another company (Japanese) has a very expensive unit that will heat based on a 9.6 gallon per minute flow rate. However, the unit is 2,000 dollars and the warranty is for one year. The manufacturer states that they could not be approved for a longer warranty because they are new to the US, but have been in Japan for over 15 years. Sounds suspect to me, but it may be my only choice. Can anybody give me some advice. Thanks> M.J.