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  1. #14
    Join Date
    Mar 2008
    Posts
    21
    Buck

    My tankless is direct horizontal vent outside maybe 3 feet max. Do you know if there is a condensate problem on these the same as vertical or longer runs?? I tried to contact Rinnai about supply temp. limits to the heater but have not heard back....

  2. #15
    Join Date
    Mar 2007
    Location
    Connecticut
    Posts
    104
    Quote Originally Posted by firefly View Post
    Buck

    My tankless is direct horizontal vent outside maybe 3 feet max. Do you know if there is a condensate problem on these the same as vertical or longer runs?? I tried to contact Rinnai about supply temp. limits to the heater but have not heard back....
    3 feet is good and should help a lot. Make sure you dont exceed the number of elbows the unit is typically allotted (for equivalent lengths) - usually 3 - 45 degree elbows allowed, and the closer they are to each other, the greater the restriction.

    Check the manufacturers websites. They usually have PDF copies of their equipment installation manuals and specification available and is the first thing everyone should look at when choosing and installing equipment for their applications.

  3. #16
    Since I am using the tankless after the Marathon holding tank how should I size the tankless for a 3 bathroom, 4 person house?

  4. #17
    Join Date
    Mar 2007
    Location
    Connecticut
    Posts
    104
    Quote Originally Posted by jhartbarger View Post
    Since I am using the tankless after the Marathon holding tank how should I size the tankless for a 3 bathroom, 4 person house?
    What is the raw (cold) entering water temperature into your house (from well or city) and how many showers do you typically operate coincidentally?

    Most of the time you could probably get away with the smallest unit they make, and this may actually be the best choice, but you can look at the GPM versus temperature rise charts to see how many GPM the device can deliver at 106-108 degrees.

    Most modern shower heads are rated at 2.5 GPM flow, so if you can tolerate 108 degree water (pretty hot), and you are using 2 showers at 100% hot water, and your entering water temperature is 50 degrees, then you would need 5 GPM at ~ 58 degree temperature rise.

    Most of the charts and settings are for 120 degrees, so if the unit will deliver
    3 GPM at a 70 degree rise (50 in, 120 out), then this should be close because you are mixing at the shower valve with cold water. If you have the shower valve at 75%, then you need .75 x 5 GPM or 3.75 GPM of 70 degree temperature rise.

    I know a lot of plumbers who are afraid to install these units because they say they don't make enough hot water, yet these are rated at, and have higher BTU output (150 to 175k) for H20 than most big boilers (usually 60 to 100k output)!

    You have an advantage of the Marathon tank, so your entering water will be a LOT hotter most of the year, so your units rating will be almost twice of what is published - in other words, you could probably double the GPM load with no noticable effects.

  5. #18
    Quote Originally Posted by Buck_Taylor View Post
    What is the raw (cold) entering water temperature into your house (from well or city) and how many showers do you typically operate coincidentally?

    Most of the time you could probably get away with the smallest unit they make, and this may actually be the best choice, but you can look at the GPM versus temperature rise charts to see how many GPM the device can deliver at 106-108 degrees.

    Most modern shower heads are rated at 2.5 GPM flow, so if you can tolerate 108 degree water (pretty hot), and you are using 2 showers at 100% hot water, and your entering water temperature is 50 degrees, then you would need 5 GPM at ~ 58 degree temperature rise.

    Most of the charts and settings are for 120 degrees, so if the unit will deliver
    3 GPM at a 70 degree rise (50 in, 120 out), then this should be close because you are mixing at the shower valve with cold water. If you have the shower valve at 75%, then you need .75 x 5 GPM or 3.75 GPM of 70 degree temperature rise.

    I know a lot of plumbers who are afraid to install these units because they say they don't make enough hot water, yet these are rated at, and have higher BTU output (150 to 175k) for H20 than most big boilers (usually 60 to 100k output)!

    You have an advantage of the Marathon tank, so your entering water will be a LOT hotter most of the year, so your units rating will be almost twice of what is published - in other words, you could probably double the GPM load with no noticable effects.

    Water is coming in from a Well and usually only one shower at a time will be run but I am sure there are times where there will be two running at the same time. So with that said I am assuming I can get away with a smaller .92 effic unit and prob be good to go?

  6. #19
    Join Date
    Mar 2008
    Posts
    21

    Smile

    I have a Rinnai R85. I believe 188k btu rated at 8.5 gallons max depending on rise. Any way, in a 4 bedroom house. I intentionally have run dishwasher with two showers going and it handles all with no problem. I actually run at 110 most times and this is fine for us. Might save a little gas...All should be much better once Marathon is inline. Also J.Hartbarger my propane feeds the tankless and gas range and my use is about 150-160 gallons per year with 2 adults/2 infants.

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