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What is the most affordable way to get hot water across the house faster with a tankless system?

Havoc
Havoc Member Posts: 8
Hello.

We had a Rinnai RL75i installed in our new home. So far we have heard of two ways to get faster access to hot water in rooms that are far from the unit. One is continual recirculation and the other uses a wireless transmitter / button to depress some minutes before using hot water. The second is more affordable than the first but still pricey. Has anyone found another and more affordable solution?

Thanks.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,918
    Not yet. Perhaps more to the point, I'm not at all sure that the second option -- firing the tankless up before drawing water from it -- would speed things up particularly. Think about it: you open the tap, water starts to flow, the tankless fires and, true to the advertising, the water coming out is almost instantly hot. But... the slug of cold water in the pipe still has to make it all the way across the house to the tap before that hot water gets there. Where's the improvement?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Leon82
    Leon82 Member Posts: 684
    If you don't want to recirculation Loop, they sell a kit with a pump and a switch that when you push the button the pump forces the hot water into the cold pipe causimg the tankless to run and send hot water to the faucet. there was a video on This Old House I saw years ago
  • hot_rod
    hot_rod Member Posts: 21,858
    could you add a small buffer tank? That seems to handle the cold slug, and provides a way to recirc.

    I think some of the tankless manufacturers show that detail.

    Kind of defeats the point of a tankless somewhat.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    delta TSolid_Fuel_Man
  • Havoc
    Havoc Member Posts: 8

    Not yet. Perhaps more to the point, I'm not at all sure that the second option -- firing the tankless up before drawing water from it -- would speed things up particularly. Think about it: you open the tap, water starts to flow, the tankless fires and, true to the advertising, the water coming out is almost instantly hot. But... the slug of cold water in the pipe still has to make it all the way across the house to the tap before that hot water gets there. Where's the improvement?

    I think that the advantage or improvement is water conservation -- important in drought-stricken areas and areas where there's a water shortage or water is expensive. You don't have to waste gallons water as the cold water runs down the drain while waiting for the hot water to arrive. You press the button, then do something for a few minutes, then turn on the tap for instant hot water; meanwhile, the slug of cold water returns and gets recycled.
  • Havoc
    Havoc Member Posts: 8
    Leon82 said:

    If you don't want to recirculation Loop, they sell a kit with a pump and a switch that when you push the button the pump forces the hot water into the cold pipe causimg the tankless to run and send hot water to the faucet. there was a video on This Old House I saw years ago

    This sounds like the second option I mentioned, but if I'm wrong, please elaborate with more details. Thanks.
  • Havoc
    Havoc Member Posts: 8
    hot rod said:

    could you add a small buffer tank? That seems to handle the cold slug, and provides a way to recirc.

    I think some of the tankless manufacturers show that detail.

    Kind of defeats the point of a tankless somewhat.

    I've been wondering if it might be possible to add a small tank. It would be interesting to hear if someone has done that and is happy with the results and costs. It would require a plumber to set it up and somehow merge the two water supplies, right? In the end with the parts and plumber charge, I wonder if it would end up costing as much as the second option I mentioned.

    Thanks.
  • hot_rod
    hot_rod Member Posts: 21,858
    edited December 2016
    Havoc said:

    hot rod said:

    could you add a small buffer tank? That seems to handle the cold slug, and provides a way to recirc.

    I think some of the tankless manufacturers show that detail.

    Kind of defeats the point of a tankless somewhat.

    I've been wondering if it might be possible to add a small tank. It would be interesting to hear if someone has done that and is happy with the results and costs. It would require a plumber to set it up and somehow merge the two water supplies, right? In the end with the parts and plumber charge, I wonder if it would end up costing as much as the second option I mentioned.

    Thanks.
    I'll keep looking for that piping schematic with the small buffer. i thought Jack with Rinnai had posted it once.

    Here are a few other options they show.

    https://www.rinnai.us/tankless-water-heater/recirculation-solutions

    https://www.bradleycorp.com/sizing-tankless-water-heaters/on-demand-heater-with-buffer-tank
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Havoc
    Havoc Member Posts: 8


    I'll keep looking for that piping schematic with the small buffer. i thought Jack with Rinnai had posted it once.

    Here are a few other options they show.

    https://www.rinnai.us/tankless-water-heater/recirculation-solutions

    https://www.bradleycorp.com/sizing-tankless-water-heaters/on-demand-heater-with-buffer-tank


    Hope you can find that schematic.

    I had seen that Rinnai page with recirc solutions. I might ask our plumber about them, in case he isn't familiar with all the options. Thanks.
  • hot_rod
    hot_rod Member Posts: 21,858
    here is the article I was searching for.


    http://www.chandlerdesignbuild.com/files/fhbDecJan08.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Havoc
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Would an electric point of use under the sink also do the job? I've monitored one to see what the electric consumption with no draw of water for a few days. It is quite impressive at how well insulated they are. Should be a cheap install and cheap to operate as it would be filled with hot water from Rinnai.

    Downside is it only takes care of one distant location.

    Taylor
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
    Havoc
  • Jamie Hall
    Jamie Hall Member Posts: 22,918

    Would an electric point of use under the sink also do the job? I've monitored one to see what the electric consumption with no draw of water for a few days. It is quite impressive at how well insulated they are. Should be a cheap install and cheap to operate as it would be filled with hot water from Rinnai.



    Downside is it only takes care of one distant location.



    Taylor

    They're wonderful -- provided you have an electrical feed to the area which can handle the power draw...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    All that I have seen/installed (only installed 2) were 1500 watts and plugged into regular 120v outlet. That's 12 amps, so won't completely tie up a 20amp circuit.

    Taylor
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • Dave H_2
    Dave H_2 Member Posts: 545
    Havoc,

    Recirc, Recirc, Recirc.
    Whats the distance to the furthest fixture?
    With a circulator properly sized and setup on a users command like a button or motion sensor, typical run time of the circ is not minutes, but more like 20-45 seconds.

    For tankless applications, the best option is a large circulator like a 0011, the larger one is needed because of the higher flow rate needed across the water heater in order to trigger it to fire.

    And you don't need a recirculation line installed.
    Take a look here taco-hvac.com/products/systems/instant_hot_water/genie/index.html


    Dave H.
    Dave H
    Havoc
  • hot_rod
    hot_rod Member Posts: 21,858
    Keep in mind with some add on systems you will be turning your cold lines warm. So if you open a cold faucet tap, you will get warm water until that line is purged.

    Sort of switching the problem from one pipe to another, where you need to flush warm from the cold. Perhaps the same amount of wasted water and wait time?

    The "on demand" logic solves some of that, but is still not a substitute for a dedicated return recirc line.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Havoc
  • Leon82
    Leon82 Member Posts: 684
    I have a 4 gallon ariston as my recirc tank. The tankless enters the loop with a brass check valve. The tankless heater does not run during recirculation. Recirculating thru a tankless may void the warranty.

    I used the diagram in my manual similar to this
  • Dave H_2
    Dave H_2 Member Posts: 545
    I agree in having a dedicated return line if its possible to install. The Genie system tries to minimize the hot water in the cold line by using a temp sensor at the circulator inlet.
    Now whats interesting in its operation is that it is not looking for a certain temp (which would add more "hot" to the cold) but it looks for about an 8 degree temperature rise from when it was activated.
    For example, if the water has not been used for a period of time (both hot or cold) the temp would be room temp. If the Genie gets activated, the start temp is 70 and the circulator will shut off at 78. This way preventing hot water from entering the cold line.
    The Genie is designed and manufactured with several choices of circulator sizes;
    006 for dedicated return line system and a tank style water heater
    008 for "cross-over" systems using cold supply as the return and small tankless water heaters and a max distance of 60' away
    0011 for cross-over and larger tankless heaters and a distance over 60'

    As long as the proper circ is chosen, it shouldn't void any warranty but of course ask the manufacturer, they are familiar with the Genie system.
    Dave H
    Havoc
  • Havoc
    Havoc Member Posts: 8
    Dave H said:

    Havoc,

    Recirc, Recirc, Recirc.
    Whats the distance to the furthest fixture?
    With a circulator properly sized and setup on a users command like a button or motion sensor, typical run time of the circ is not minutes, but more like 20-45 seconds.

    For tankless applications, the best option is a large circulator like a 0011, the larger one is needed because of the higher flow rate needed across the water heater in order to trigger it to fire.

    And you don't need a recirculation line installed.
    Take a look here taco-hvac.com/products/systems/instant_hot_water/genie/index.html


    Dave H.

    It's approx 70' to furthest fixture. There are two bathrooms in question, but it might only be practical to recirc to one of them.

    Hadn't heard of the Taco genie. Will investigate that. Thanks.
  • Havoc
    Havoc Member Posts: 8

    Would an electric point of use under the sink also do the job? I've monitored one to see what the electric consumption with no draw of water for a few days. It is quite impressive at how well insulated they are. Should be a cheap install and cheap to operate as it would be filled with hot water from Rinnai.



    Downside is it only takes care of one distant location.



    Taylor

    This is indeed a possibility, and there is an electrical outlet available. Thanks for the tip!
  • Havoc
    Havoc Member Posts: 8

    Would an electric point of use under the sink also do the job? I've monitored one to see what the electric consumption with no draw of water for a few days. It is quite impressive at how well insulated they are. Should be a cheap install and cheap to operate as it would be filled with hot water from Rinnai.



    Downside is it only takes care of one distant location.



    Taylor

    They're wonderful -- provided you have an electrical feed to the area which can handle the power draw...
    We do have an electrical feed that can handle it. Thanks.