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Radiant: zero delta ?

TAG Member Posts: 609
While I have done many houses with radiant -- have never done a whole house with only radiant. Have also never used a condensing wall boiler. Viessmann 200 in this case.

So my question: It seems that after playing with the system now for some weeks. The goal should be to pump so as to get as close to zero delta as possible.

Am I missing something?

When the temps were down around 15 -- I had the whole place almost a perfect 65 (it's under construction) with just some slight tweaking of the flow. Surprised it was working so well.

Looks like all my expensive controls may be a waste -- key was keeping the supply alpha pump on high (pressure - not speed) Running about 43 watts. Have the boiler loop on speed 2. This gave me more flow to all the loops and a very small delta.


  • Zman
    Zman Member Posts: 7,328
    I think you are thinking about this backwards. BTU/Hrs = Delta T x GPM x 500.
    On the emitter side a delta of ~10 degrees once it has reached steady state is a good goal for a comfortable even heat.
    On the boiler side, you will run more efficiently with higher delta and lower flows.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    EBEBRATT-Ed Member Posts: 11,987
    The heat transfer from the emitters doesn't change much with the flow. High flow lower delta, low flow higher delta heat output doesn't change much