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Heat exchanger sizing

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BenG
BenG Member Posts: 10
edited October 2019 in Radiant Heating
My first post was about adding more zones to my radiant system. That is complete now.

I added one more pump with two zones to an existing one pump, one zone 1000 sq ft. Radiant system. The problem I have now is that when all zones call for heat I am maxing out water temp at 90F with 140f going into a heat exchanger the 90f is the water temp for all areas. If I shut off the main radiant system water temp increase to 110-120. That is not ideal though.

How do I increase the heat transfer? New heat exchangers? Pipe sizes? Flow rates?

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  • Zman
    Zman Member Posts: 7,569
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    The answer is that you have to consider all of the above. Whatever you do, do not size the exchanger based on the generic rating printed on the exchange.
    Most manufactures have an on line calculator which allows you to input your key requirements and will make the selection for you. I like this one, http://flatplateselect.com/site/pub/login.aspx?ReturnUrl=/site/default.aspx, others may have there own preferences.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • BenG
    BenG Member Posts: 10
    edited October 2019
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    Thanks. I am leaning towards upgrading the HE because a) I maxed out boiler temp at 140, increased all pumps to HI setting and with all zones running cannot get water temp past 90 on the radiant side. b) With only the main 1st floor (1000 sq. ft) radiant system running water temp max is 90 and its a very slow climb. c) with only one or both of the smaller secondary zones running water temp quickly reaches 120F.

    A, B, & C indicate to me that my HE is undersized. and it was for the original zone. Do you agree?

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