Tankless layout/sizing question

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ttraversnj

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We are getting towards the end of our house build and I recently hooked up the kitchen sink. I had to wait 2 minutes for hot water. I had a Rinnai tankless unit installed a few months before. It's an RL75i. We have 3 full bathrooms, a half bath and a shower in the utility room. So you could say 4 bathrooms...I realized that I probably purchased the wrong Rinnai unit. Besides the water sandwich in the kitchen, I'm worried about not having enough water for 2 showers and more running at the same time. The one shower I have hooked up also went cold on me a few times which I thought was very strange....I have a well. I don't have a return line. At this point I might be able to put a return line in but I would have to open a few walls(the house isn't completely finished, I don't mind spackling if I have to). The return line would be a 45 to 50 ft straight run from the kitchen to the utility room. It would be very easy if I could run the return line outside the house? If thats even an option...I'm in the North Georgia mountains.. Then I started reading about the grundfos comfort systenm...cross over recirculation....... So at this point I'm wondering the best way forward. I don't want to waste money but having this done right is the top priority. Options: 1. New larger tankless unit with built in recirculation, 2. same unit with either new recirc line or cross over... with a pump or 3. add another unit and have 2 units?? as you can see it's confusing the hell out of me. Thanks for any input. Tom
 

Fitter30

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Page 2 is temp rise to flow 75° @4 gpm. Whenever sizing this type of heater need to know max gpm and coldest water temp. Return line will or a grundflos or others will help with the time to get hw but won't do anything for volume. Even the largest 199k might not meet your needs. Storage tank 50 - 75 gallons with recirculation pump through the Rinnia to heat the tank and then a return line or system back to tank. Check with Rinnia tech and use with storage tank.
 
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