Best Of

As they say there is no free lunch. The free boiler will cost you more than getting the right unit.

The issue is all the bits you need to make this work properly will be near the cost of a new modcon. If your fuel source is expensive like propane, the operating cost delta is not worth the effort (properly set up modcon will use about 25% to 30% less fuel with radiant).

"The entering temps from the loops vary. Normally 35 in winter and 72 or so in summer."

To me that's a severe red flag that the well is insufficient, or something is wrong with the way it's piped. If the well water is only 35F in winter there's almost no heat available before the water freezes. In Pennsylvania I'd expect the year-round ground temperature to be in the low 50's and the well water should stay at that temperature if the wells are property configured.

A standard circulator, like a Grundfos UPS15-58, is what’s used for the injection pump. The mixing control (usually a Tekmar’s 356) controls the speed of the pump.

With the return sensor added, the control provides boiler protection as well as ODR.

As hot_rod mentioned, Buderus boilers are made from a specially formulated cast iron that’s actually flexible. They can withstand return water temperatures as low as 106* without damage from thermal shock. However, you don’t want to continually run it that low because of flue gas condensation. A constant temp of 140* should be sufficient. You don’t need 180* unless it’s being vented into an over sized masonry chimney or when the indirect needs quick recovery.

OP may want to consider while tearing up the kitchen taking that radiator out, sandblasting and repainting. It is a very nice radiator. I personally have never been a fan of the white paint since it shows dust an dirt so much…

@amaiale , take a pic from the end of the radiator so we can see what type and capacity are the sections it uses. Also how tall is it?