replacing 1 large boiler with 2 smaller ones

dronic123

Thanks for your interest and comments. A special shout-out to @bburd and @Kaos for their posts about temperature control of the system loop. As a newbee, this was all news to me and I really didn't understand that concept at all right away. The talk always seems to be about boilers being too large and oversized and I thought 2 smaller boilers was a way to modulate so that the working boiler boiler would suit the load. But I have now re-read the post several times and finally watched a couple of videos. There is even a whole idronics article about it, so it seems really quite main stream!

But I have a question: I can see how the return water entering the system without going through the boiler will now "cool" down the initial rads it interacts with but overall the system has just so many btu's in it and they are not going anywhere except into the house . Yes the system is not going to get any more btu's from the boiler and that is a good thing—— but the system is only going to cool down by releasing the heat into the house and not really from the return water which should only be 20 degrees cooler than the initial supply temperature to start with.

There is the huge advantage of decoupling the boiler from the system loop and allowing it to heat up to 130-140 degrees and not affect the system loop, wow- yes, yes, yes, but I don't see how the return water is going to cool down the rads much more than if you just shut off the boiler. Maybe the "cool down the system" is just a term of art??

Is the answer maybe that the ODR turns on the mixing valve before the heat gets into the rads?

When the mixing valve is "at rest" at room temperature is it half open on each side or is it open on one particular side and closed on the other?—anyone know?