I am thinking about installing a demand hot water heater for my home. I have a high GPM demand for my shower with multipule heads. I need about 13 GPM at 105 degrees. I was told that I would need three units to get this GPM. This is very expensive way to go. Any other suggestions. I currently have a 75 gallon gas Hot water heater that does not provide enough hot water in the winter. Any suggestions? I would like to be as efficient as possible.

I'd get more quotes from several installers who work with Rinnai and Rheen and other top brands. http://www.rinnai.us/Rinnai/FileLibr...lsseries_1.pdf This one unit is rated at 9+ gpm so two would be more than you need. Other brands may have larger unit that I have not installed. How did you get your 13 gpm, seems high to me.

13 GPM for a shower is a bunch of water and one really expensive shower but if that is what you enjoy go for it. Years ago I used the old style Paloma water heaters to do a built in pool and a shower system similar to yours plus heat the 6000 sq ft home with hot water fan coils. They worked geat but I did rely on a water stack tanks (two 100 gallon tanks) for reserve and a mix down system. Use a 1 and 1/2 inch copper header to tie them all together.It is still in operation today last I heard.

Paloma Tankless Water Heaters by Low Energy Systems

GREAT recovery

171 gallons/hour
100°F rise Per unit

On Demand Gas and Propane Paloma Tankless Water Heaters by Low Energy Systems

These units are very simple to repair also.