Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

new tankless system

Stan123 Member Posts: 1
I'm considering installing a tankless system as part of a home renovation but don't know how big of a unit i will actually need.  Will have a pretty active household using hot water in 3.5 baths, dish washer and laundry.  How many GPM's will I really need?  Should I be considering multiple units with point of use heaters as well? I'm located in the North East, so temp, rise, as I understand it, is also going to be a concern.  thanks  for  the input


  • TonyS
    TonyS Member Posts: 849
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Tankless Sizing

    Here is the formula

    GPM Required x Temp Rise x 500 = Btu's needed

    What's in those 3.5 baths? Basic 2.5gpm shower heads? Body Sprays? Any whirlpools? How many of those showers are running at once. Let's say 2 of them and they have basic heads.

    2.5 x 2 = 5

    Now let's add another 2.5gpm in case the wife decided to run the dishwasher or someone turns on a kitchen sink. That gives us 7.5gpm. Most laundry is done in cold water so we won't worry about that.

    7.5gpm x Temp Rise

    Temp rise is the difference between the incoming cold water temp coming from the street or well (IN THE WINTER) and the water temperature I want to make.

    Let's say the incoming temp is 50 and I want to make 110 degree water. My temp rise is 110-50 = 60

    7.5gpm x 60 x 500 = 225,000 btu's an hr. I need an on demand water heater that has the ability to produce 225,000 btu's an hr when every fixture calls for hot water.

    There was an error rendering this rich post.

This discussion has been closed.