Announcement

Announcement Module
Collapse
No announcement yet.

Rinnai tankless water heaters

Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts

  • Rinnai tankless water heaters

    We are thinking about installing either a Rinnai R98LSi or R94LSi. We have a two bath house and live in Indianapolis, IN. My wife and I have two very young boys and expect to add a third kid in the next two years. We want to plan for the future when purchasing our tankless water heater. So, we are trying to decide if we will want or need the larger capacity of the R98 in the winter when the boys get older.

    Here are my questions.
    1. Given our situation, will the R94 satisfy our hot water demands or should we move up to the R98?
    2. How do the two water heaters compare in terms of efficiency and gas usage? For example, will the R98 and R94 use the same amount of gas when heating water for one shower?
    3. What is the significance of a minimum gas flow rate of 19,000 (R98) versus 15,000 BTUs (R94)?
    4. Are there any differences in performance (other than hot water capacity) that I should be aware of?

    Any help in answer these questions will be greatly appreciated. Thank you!

  • #2
    Re: Rinnai tank less water heaters

    the best answer that i can give you is to call rinnai and connect to there engineering department tankless is an interesting topic on most forums people love em or hate em, we service and install them regularly in south carolina but our delta t is a lot more kind than you all in the northern states, rinnai can give you straight answers and that will help you make the best decision without confusion or misleading you . good luck

    Comment


    • #3
      Re: Rinnai tankless water heaters

      I don't know much about the Rinnai heaters but I did install a Takagi TK1 tankless in my home and they all generally operate in a similar manner. So regarding questions 2 and 3.

      2 - Yes, they should be about the same. Tankless heaters use a modulating gas valve which can adjust the size of the flame in the burner depending on the water flow in order to maintain a set temperature. For the same shower and the same temp the amount of energy required to heat the water should be roughly the same. It won't be exact since the losses in the heater won’t be exactly the same but it should be close.

      3. The min btu refers to the min size of the flame - if it goes any lower the burner cannot sustain combustion and will shut down. This translates to a min flow allowed. For example if you simply run a trickle of water, the tankless will shutoff. This is one of the differences between tanks and tankless - with a tank you can just have a trickle and still have hot water. The difference in the 2 specifications means that for the one with the larger number you will need a slightly larger flow below which the burner will shut down.

      Comment


      • #4
        Re: Rinnai tankless water heaters

        what's wrong with your present tank heater situation?

        what's the cost difference between the tank and tankless install?

        do you really want a tankless?

        i would really think twice about a tankless. and yes i own one just for the benefit of testing in my house.

        i would not recommend it for most installations. although i've installed 2 others as there was no other feasible choice.

        rick.
        phoebe it is

        Comment


        • #5
          rick is right

          the old saying of "measure twice cut once" comes into play here. breid...............

          Comment


          • #6
            Re: Rinnai tankless water heaters

            Do You need to run a larger gas line? Are You sure? Elec. out =no hot water !
            Good luck
            I can build anything You want , if you draw a picture of it , on the back of a big enough check .

            Comment


            • #7
              Re: Rinnai tankless water heaters

              Originally posted by PLUMBER RICK View Post
              what's wrong with your present tank heater situation?

              what's the cost difference between the tank and tankless install?

              do you really want a tankless?

              i would really think twice about a tankless. and yes i own one just for the benefit of testing in my house.

              i would not recommend it for most installations. although i've installed 2 others as there was no other feasible choice.

              rick.
              Thanks everyone for the responses. We are looking at tankless because of space issues. It is such a tight squeeze in our utility closet that a new tank will not fit (our current 15 year old tank, which came with house, is undersized). We do not want to give up space elsewhere in the house for a tank, so we are considering the tankless.

              Comment


              • #8
                Re: Rinnai tankless water heaters

                Originally posted by toolaholic View Post
                Do You need to run a larger gas line? Are You sure? Elec. out =no hot water !
                Good luck
                We are having a gas line put in. The gas company will lay it for free if we hook up a gas water heater.

                Comment


                • #9
                  Re: Rinnai tankless water heaters

                  Well here is a couple questions that will help us answer your questions.
                  1. You currently have 2 baths. Do you plan on adding on another bathroom?
                  2. What is you incoming water temperature?
                  I am going to assume that your incoming water temperature is close to what it is here in Chicago 45º F So to get a 120º F output you will need a 75º temperature rise. So with the models you listed:
                  • R98 will flow 5.2 gpm @ 75º rise
                  • R94 will flow 4.6 gpm @ 75º rise
                  If both showers are being used at the same time and you have a standard shower system that flows 2.5 gpm each you will be trying to draw a total of 5 gpm that is only if you run full hot on both showers. Most people shower at 110º and modern shower valves supposed to have a temperature limit set to no hotter than 115º per most plumbing codes. With these numbers we can figure in an 8% difference in the flow rate when both showers are running which would bring the 5 gpm down to the 4.6 gpm So the R94 would do the job but you will be running it to its limit. If some one started doing dishes or laundry, in other words opened another hot water tap in the home the water heater will still flow the 4.6 gpm to all fixtures so the pressure will drop between all three fixtures. Even the R98 would not help if you decided to run three fixtures at once since it is only providing you an additional 0.6 gpm.

                  Now what I would suggest, especially if you do plan to add a third bath or you can foresee that both showers and laundry will be running at the same time is to install a pair of R75 units. This will give you many advantages. First of it will provide if needed a full 8 gpm flow rate which will be more than enough for your home's needs. Secondly redundancy, meaning if for any reason one of the units go down you will have the other unit to keep you going will the down unit is getting serviced. Do not worry about both heaters running all the time it does not work that way. When you run one fixture the unit firing first that day will only fire enough BTU's to provide you the 120º water, as it reaches 70% of its capacity it will then tell the other heater to kick in and help They both will not run full BTU's, again just enough to provide you with the flow rate that is being demanded at the time. Now the units alternate which ones fires first every 24 hours hours or every 8 times it fires up, this way they both will always get equal usage.

                  Now here is a few things to consider also. If you have a front load washing machine that uses short bursts of water, you may need to install a buffer tank to help it along. Showers with pressure balancing systems may be a problem with temperature fluctuations if you undersize the heater. You can either properly size the tankless heater system or replace your shower valves with temperature balancing valves instead.

                  I do hope this post was helpful to you and your family.
                  Ron Hasil Lic #058-160417
                  A-Archer Sewer & Plumbing specializing in:
                  Tankless Water Heaters | Drain and Sewer Cleaning
                  Sump and Ejector Pumps | Backflow RPZ Testing

                  Comment


                  • #10
                    Re: Rinnai tankless water heaters

                    Originally posted by SewerRatz View Post
                    Well here is a couple questions that will help us answer your questions.
                    1. You currently have 2 baths. Do you plan on adding on another bathroom?
                    2. What is you incoming water temperature?
                    I am going to assume that your incoming water temperature is close to what it is here in Chicago 45º F So to get a 120º F output you will need a 75º temperature rise. So with the models you listed:
                    • R98 will flow 5.2 gpm @ 75º rise
                    • R94 will flow 4.6 gpm @ 75º rise
                    We do not plan on adding a third bath and our incoming water temperature is comparable to Chicago. On the brochure I have from Rinnai, I am getting slightly different flow rates than what you list:
                    R98 - 5.3 gpm @ 75 degrees
                    R94 - 4.4 gpm @ 75 degrees
                    Still, your point is well taken.

                    If some one started doing dishes or laundry, in other words opened another hot water tap in the home the water heater will still flow the 4.6 gpm to all fixtures so the pressure will drop between all three fixtures. Even the R98 would not help if you decided to run three fixtures at once since it is only providing you an additional 0.6 gpm.
                    In your example with three fixtures, I assume the temperature at each fixture will drop along with the drop in pressure. So, you would not just have a decrease in water flow, but a decrease in temperature as well. Is that correct?

                    Now what I would suggest, especially if you do plan to add a third bath or you can foresee that both showers and laundry will be running at the same time is to install a pair of R75 units.
                    This is an interesting solution and I appreciate all the advantages you list. Can you give me a rough estimate on how much more it would cost as opposed to a single tankless? Will I need separate intake and exhaust pipes for each water heater? Will a pair of units cause any temperature fluctuation problems or affect the minimum flow rate?

                    Now here is a few things to consider also. If you have a front load washing machine that uses short bursts of water, you may need to install a buffer tank to help it along.
                    How big does the buffer tank have to be? Will the buffer tank also help with the cold water sandwich, minimum flow rate, and temperature fluctuations?

                    I do hope this post was helpful to you and your family.
                    That was all very helpful! Thank you!

                    Comment


                    • #11
                      Re: Rinnai tankless water heaters

                      Originally posted by jg nothing View Post
                      We do not plan on adding a third bath and our incoming water temperature is comparable to Chicago. On the brochure I have from Rinnai, I am getting slightly different flow rates than what you list:
                      R98 - 5.3 gpm @ 75 degrees
                      R94 - 4.4 gpm @ 75 degrees
                      Still, your point is well taken.

                      That was all very helpful! Thank you!
                      I went off the chart from their online spec sheets, so my numbers are my best estimate of where the line crosses the flow chart.



                      Originally posted by jg nothing View Post
                      In your example with three fixtures, I assume the temperature at each fixture will drop along with the drop in pressure. So, you would not just have a decrease in water flow, but a decrease in temperature as well. Is that correct?
                      The way a tankless water heater will work is it will not flow no more than gpm that is needed to provide you the set temperature. If you have a R94 installed the heater will only allow 4.4 gpm to flow through the unit so it can always give you the 120º water output. So as you turn on more fixtures you are dividing up that flow, lets say you opened 4 fixtures that are flowing 2 gpm each for a total flow rate of 6 gpm. Now the heater is only providing you with 4.4 gpm Whats going to happen is each fixture is only going to get 1.1 gpm in this example but it will still be the set temperature.


                      Originally posted by jg nothing View Post
                      This is an interesting solution and I appreciate all the advantages you list. Can you give me a rough estimate on how much more it would cost as opposed to a single tankless? Will I need separate intake and exhaust pipes for each water heater? Will a pair of units cause any temperature fluctuation problems or affect the minimum flow rate?
                      It will not affect the minimum flow rate at all, and it would not cause any temperature fluctuations. They both have to have their own vents. As to cost Its an extra two hours in labor a few extra plumbing fittings and a second heater with vent pipes. The R75 is less expensive than a R98, which means the cost of two R75's will be a little more than a R98. Last double tankless install I did including all the gas pipe and vent work cost a little more than a third more than a single unit.



                      Originally posted by jg nothing View Post
                      How big does the buffer tank have to be? Will the buffer tank also help with the cold water sandwich, minimum flow rate, and temperature fluctuations?
                      In most cases a 6 gal 110V electric heater works real well as a buffer tank and it does help prevent the cold water sandwich, Minimum flow rate is what the heaters are rated it, If you are doing a short small draws this will help deal with that issue.
                      Ron Hasil Lic #058-160417
                      A-Archer Sewer & Plumbing specializing in:
                      Tankless Water Heaters | Drain and Sewer Cleaning
                      Sump and Ejector Pumps | Backflow RPZ Testing

                      Comment


                      • #12
                        Re: Rinnai tankless water heaters

                        Thanks SewerRatz for the information. It was really, really useful. I have one more set of questions (hopefully) for you or anyone else. Is there a significant difference between Rinnai HP and LS series in terms of performance? The HP series is a new line of "ultra efficient" condensing water heaters. I noticed that there are differences in the specs of the HP and LS.

                        RC98HPi
                        min/max gas rate = 9,500 / 199,000 BTU/hr
                        minimum flow rate = 0.4 gal/min @ 50 and 35 degree rise
                        thermal efficiency = 95%

                        LS98
                        min/max gas rate = 19,000 / 237,000 BTU/hr
                        minimum flow rate = 0.6 gal/min @ 50 degree rise and 0.9 at 35 degree rise
                        thermal efficiency = 84%

                        It seems that the RC98HPi has better specifications. Will it perform better overall? Is there any reason not to prefer the HP over the LS? Do you think there are any performance tradeoffs for the HP that Rinnai is not mentioning?

                        Thanks again to everyone who has replied to my posts. This has been a great education!

                        - Johnny

                        Comment


                        • #13
                          Re: Rinnai tankless water heaters

                          From what I could tell the RC98 is a redesigned R94 unit with duel heat exchangers to make it a bit more efficient. I have not seen one in person yet. When i get back from the trade show I will call my Rinnai rep and schedule a meeting with him about the new units and I will post what I learn here.
                          Ron Hasil Lic #058-160417
                          A-Archer Sewer & Plumbing specializing in:
                          Tankless Water Heaters | Drain and Sewer Cleaning
                          Sump and Ejector Pumps | Backflow RPZ Testing

                          Comment


                          • #14
                            Re: Rinnai tankless water heaters

                            Originally posted by SewerRatz View Post
                            From what I could tell the RC98 is a redesigned R94 unit with duel heat exchangers to make it a bit more efficient. I have not seen one in person yet. When i get back from the trade show I will call my Rinnai rep and schedule a meeting with him about the new units and I will post what I learn here.
                            Thanks! My contractor says there was some concern by Rinnai about the exhaust temperature of the condensing unit rising over a period of time as the unit gets older. Consequently, the PVC piping might eventually fail.

                            I think we are going with the R98LSi. I assume (and hope) the slightly higher minimum gas flow rate (19000 BTU/hr for the R98 versus 15000 BTU/hr for the R94) is not going to make too much of a difference. Is an extra 4000 BTU/hr going to make a noticeable difference in performance?

                            Comment


                            • #15
                              Re: Rinnai tankless water heaters

                              JG, I've also been looking at the RC line. For what it's worth, the vent pipes for the Rinnai RC line aren't PVC, they're polyproylene. They're also more expensive than PVC, but not as expensive as the venting needed for the other Rinnai lines.

                              Comment

                              Working...
                              X