Should wood boiler be in parallel with existing boiler?

BigMacWisconsin · January 22

Hey everyone,

I recently changed my system to install a heat exchanger separating the the systems which solved my issue of not regulating temperature well. When reading how to connect them, I kept seeing that you should not connect them in parallel because it limits the max temperature of the inside boiler core, which makes sense. This recent cold stretch made it difficult to keep up with the heat as the baseboard registers didn't seem to get hot enough.

My question to the group, if I change to connect the heat exchanger to be in series, does it really matter if its on the input or output of the indoor boiler? As you would expect, the plumbing would be a lot easier to connect on the outside.

Thanks!

GroundUp · January 22

We have no idea what sort of system you're working with so it's impossible to give proper advice. What make/model boilers? Pictures of the piping? If you're referring to an outdoor wood boiler and a cast iron indoor boiler, typical is to cut the HX into the return piping before it enters the CI boiler so the HX essentially preheats it prior to entering the CI boiler. Some require a "wrap around" circulator to keep the core hot at all times, but that'll depend on how it's actually piped and how the boiler is controlled.

BigMacWisconsin · January 22

OWB, woodmaster 4400 connected to an old fuel oil boiler. 3 zones, and this is how it originally was hooked up. There never was a heat exchanger when we moved in, so I connected one online with what's labeled as "OWF SUPPLY". Question is if I should move it either between the zones and oil boiler or if I could connect it on the output of the oil boiler.

Big Ed_4 · January 22

If you run one or the other , pipe in parallel with shut off valves to control . To supplement the system , pipe in wood heat exchanger on return..

leonz · January 22

https://forum.heatinghelp.com/discussion/comment/1837034#Comment_1837034

What type of forest eater do you have? is it an open to air boiler or a closed boiler?

My original wood and coal hand fed was piped in parallel with the oil boiler using a circulator to ba;lance the temperature between the two boilers.

I improved my hand feds efficiency greatly by filling the firebox volume half full of standard firebrick which created a huge heat sink that absorbed the heat from the wood or coal fire and radiated the heat back into the fire box to reduce the wood smoke to a barely noticeable smoke except when it idled when burning wood.

hot_rod · January 22

if you pipe in series, a portion of the wood fired heat goes up the cast boiler flue

So you 40% efficient OWF drops even more

And you don’t want cast boiler output going out to the OWF?

GroundUp · January 22

Typically speaking with a system that uses a draft damper, you'd cut the HX into the return just to the right of the oil boiler in your drawing as a preheat like I'd mentioned above. Back feeding is a non-issue and actually preferred for freeze protection, assuming the OWB is primary and oil is only for backup/vacation. In a system like this without a damper, you'd save some fuel (due to the flue losses as Hot Rod mentioned) by cutting in a tee to the right of the oil boiler in the return and piping a bypass around the oil boiler back to that tee in the supply where the OWB return used to be. A 3 way zone valve and aquastat could be used to switch back and forth between OWB and oil automatically, otherwise a manual ball valve could be used as well to prevent heated water from getting into the oil boiler at all. Would not recommend putting the HX in series on the supply side, either way.

hot_rod · January 22

Now if the oil boiler has a tankless coil for DHW, of course it would want to be hot always, so series piping, or some piping method to allow it to remain hot.

Should wood boiler be in parallel with existing boiler?

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