Tankless layout/sizing question

[ttraversnj]

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]

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.

https://www.google.com/url?q=https://media.rinnai.us/salsify_asset/s-22bec185-aa7e-4db7-9364-1b1d6c9bc19b/RL75i%2520(VC2528FFUD-US)%2520SP.pdf&sa=U&ved=2ahUKEwiJs-bvwvqJAxVw5MkDHchhFZoQFnoECBAQAg&usg=AOvVaw0_Ejzpk9AXNkmjQam9JyO-

 

[Sponsor]

 

[xedos]

Don’t know if you solved your issues but I have some comments based on several houses in the same area with rinnai tankless heaters.

I think your 75i is too small for your needs. A 199i will run easily 4 showers simultaneously at my ATL , and SC foothills/ mtns. places. Even in winter. And one of the showers has 6 fixtures using 10+ gpm full bore. A 75i in N.GA in winter is prob. too weak to provide 4-5gpm for two showers simultaneously. And even If it does, will be an issue when a dishwasher or washing machine or even a faucet turns on while they are both running.

The 2min wait at your sink has nothing to do with a tankless vs. tank. Hot water takes the same amount of time to travel the same distance whether it comes out of a tank or a tankless heater.

Do you have a hot water pressure tank In the system ?

DO NOT run a return line outdoors in N.Georgia !

I suspect most of your issues are related to your well/pump system and or its bladder tank.


Before I ran a return line to the kitchen for one or two fixtures - I’d explore a small elect. tank heater or on demand for under the sink on the hot water side. It should supply enough until the hot arrives from your utility room and will likely supply enough for 75- 90% of your needs there by itself. That’s a simpler, cheaper alternative to a recir. line in many cases.

What kind/type/brand shower valves do you have ?

Need to verify how much gas supply (volume) you have in your mechanical room. A 199i will use a LOT of gas during heavy demand. Shouldn’t be an issue if you have propane, but might be if your on nat. gas and your contractor /designer cheaped out on infrastructure.

 

[John Gayewski]

Get you navien 199k A2. Then get the inner sink valves that go with the Navien.