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.

Indirect water heater

Vad Member Posts: 55

       I have pretty small 2 family house. Currently it has two 15 years old Direct water Heaters, with 40Gl tank each. All together the house has 2 full bath + 3/4 bath, hot water in each of the two kitchens, one washing machine and one dishwasher.

        I am not too interested to have separate heaters for each floor.

        I am installing a new boiler. My boiler will be only about 82% eficient. I am thinking to use Indirect water heater.

Couple of questions.

  1.  Does it make sense to use Indirect Water Heater since the efficiency of the boiler is pretty low?

   2.  How big the tank for the Indirect water heater should be in order to produce equivalent amount of hot water that I had before (two 40Gl tanks with direct water heaters)?

   3.   How much BTU I should add when sizing the boiler to accommodate Indirect Hot water heater

Thank you a lot,



  • CMadatMe
    CMadatMe Member Posts: 3,086
    Added Btu

    You shouldn't add any! Zone with priority to allow all the boilers btu to make hot water. Can't anwser your question on size of indirect without knowing the boiler size and how many people. Is there the potential to have to supply 4 showers in 1hr?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Vad
    Vad Member Posts: 55
    edited September 2010
    Thank you a lot, Chris, I am overwhelmed with all this stuff

    4 showers in 1 hour is possible but it will be the maximum. I am planning to install slow flow shower heads (I will give it a try at least).

        Many web sites say that bath tube uses 4 gpm. You think it is possible to buy bath tube faucets with less than 4 gpm (2.2 or something close)?

       I probably should consider about 8 gpm flow rate (2 showers and let say 2 kitchens running water at the same time).

        I did some calculations (attached) and came to First hour rating of about 124 Gl with 2 bath tubs, 1 shower and some extra water use. If I add another shower, it will be 142.Gl

      What you think the minimum tank size can be.


     I did a heat loss calculation for my house and it is about 56K BTUs. Even if I choose 45 Gl Indirect, It is required 130K - 160K (depending on make). As I understand from your reply, it will not be a problem if I choose a boiler smaller than 130K (maybe about 100K). Will it be the problem with tank of about 60Gl (if you suggest it) that require up to 198K max (198 is for HTP brand, others require less)

    I appreciate you help,

    Thank you


  • CMadatMe
    CMadatMe Member Posts: 3,086
    Size The Boiler

    Size the boiler to the heat loss and increase storage capacity for the indirect. Instead of a 40 gal look at a 60 or 80 gal. As an example an Amtrol CH-80 will give you 147 gals in the first hour on 60,000 btu's. But also remember that is based on a 90 degree rise.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Vad
    Vad Member Posts: 55
    Thank you for reply.

    Can I know how you calculated 60 Gl?

    The other question. If I choose 40 Gl and let' s say 4 people take shower i the first hour. How long you think the last person should wait till he will be able to take a shower. Could it be longer than 10 to 15 minutes, you think?

      I have heard that if for example I miss 20Gl when I choose 40Gl over 60 Gl, I can install a storage tank to correct my mistake. Is that correct or no?

      When installing Indirect, what are the things the contractor should put an attention. What he should not miss. One thing I know is an extension tank should be installed. What else?

    Thank you,

This discussion has been closed.