Wood boiler replacement

[tuolumne]

I took out an old wood boiler; the current install appeared to work as follows...
The two boilers were piped in parallel, with the 6 zones in a manifold supply/return configuration. The oil boiler has no circ. When a zone calls, the zone pump (6 of them) operates and pulls water through the oil boiler. Presumably, the water will not tend to go through the wood boiler because of the circ. on that side of the loop. When the wood boiler was hot, it's own aquastat controled circ. will energize...if all 6 zones are calling, most of the water will go through the manifolds....if no zones are calling, water will get circulated throught the oil boiler in reverse. Again, this is theoretical behavior based on my examination of the current plumbing. This is not how I would plumb things new, but it is what we have to work with. In interest of saving money, I plan to put a new EKO in place of the existing wood boiler that was removed. Again, I would have a boiler circ (this time with a Danfoss and heat protection loop) which could behave in the same way as the old setup. Should I make the wood boiler communicate with oil or not? Right now, the oil buner fires based on boiler temp. Will the wood boiler be circulating enough heat through the oil to keep it hot based on the described piping? Otherwise, I could use the EKO controller to energize the oil boiler when the wood boiler is cold. This would be a lot of rewiring. Is it needful?

 

[WoodNotOil]

Check out my website in my signature and I think your system is very similar to mine before I added storage. On this forum this is usually refered to as a series hookup. In my experience simply setting the oil aquastat much lower than the wood one is enough to keep it from firing, most of the time. If all six zones are on however, that is a 6 to 1 ratio of return water to wood heat water. As you suggested it could be tied to an aquastat on the wood so that it knows when the wood is cold. The advantage would be that the oil would come up to 180* instead of a lower temp. That could be done rather simply. Get a close on temp decrease aquastat and feed the power that usually goes into the oil aquastat to it first. That way when the wood is hot enough the oil aquastat doesn't even get electricity and can be set to 180*. When the wood boiler get under temp, electricity goes to the oil aquastat and it comes up to 180* to meet demand.

Also, you will probably want a pump bigger than a 007 to circ between the boilers or not enough heat will reach the oil boiler for zones in a heavy demand situation. What size is in there now? You could try a variable speed pump on high or a couple of 007 in series.