OK guys, take it easy on me. This is my first post to the forum...

I am trying to do a little redesign on a house we bought with radiant heated floors last year. (The January heat bill was $425). Leaving out almost all the finer points of the redesign, my immediate question comes down to this:

    Using the calculation out of Mr. Siegenthaler's book, Modern Hydronic Heating (Second Edition),  I calculate an injection rate of about 1.44 gpm for my main floor with 32,000 btuh, a boiler running at 140F, with estimated target target supply temp to the PEX in aluminum diffusion plates of 110 and estimated return temp of 95F (heated water, so the k = approx 500).  This seems pretty low. The basement, once insulated, should have a heat loss of about 10,000 btuh so if my calculations are correct I'll have to buy my injection pump at the LEGO store (less than 0.5 gpm).

Am I doing something wrong here?
 

Thanks in advance.

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Sounds like you are on the right track.  The tiny flow rate of such an injection system is one of the challenges, this is why the installation and balancing is critical.  With the progression in technology from most of the major circulator mfgs, finding a variable speed circulator to fit your application should be a breeze.

Jay,

Thank you for the confirmation. I am probably overbuilding the system, partially to make up for the rudimentary system I inherited.

I purchased a Taco 006 pump, a mixing controller (a rebranded Tekmar) , and a (differential) balancing valve. I'm still pretty close to the corner of the pump's performance curve, but I'll have to see what that gets me.  I probably should have gone to a smaller pump (the 003), but I'm way over budget already and the smaller pumps are relatively more expensive and harder to find.

Thanks again. I'll keep reading these forums. Now, where do I find a supplier of AAAA batteries for that Lego mixing pump.