Wood-fired heat exchange to supplement boiler

mypsi

So, we just bought our house that has hot-water heating (old cast iron radiators with a gas boiler) and a fireplace.  It's an "English" fireplace, basically a romantic way to pipe warm air out of the house.  I've been thinking about how I can burn wood to effectively heat the house, and here's my grand, over-the-top, master plan:



I would like to install a cast iron fireplace insert, using an air inlet to bring oxygen in from outside for combustion.  It would have a heat exchanger (metal coils) to heat water.  This water would be somehow tied into the boiler system, not totally replacing it, so that we wouldn't have to always be burning wood, but to capture some of the heat from the fire and transfer that through the hydronic heating system.  I am familiar with outdoor wood boilers, but have not seen discussions of how to integrate them into gas boiler systems.  I have seen some mention of supplementary wood burning stoves, but always mentioned in the basement.  Is having it above the gas boiler an issue?  Would I need another circulating pump in there somewhere?



Also, I think it would be really cool to completely remove the aquastat relay altogether and replace it with some open-source software that controls the boiler, the air intake to the stove (to shut that off when it gets hot enough), the flue dampers, and the circulating pump(s).



This is long-term, pie in the sky thinking, but any advice would be great.  If anyone can refer me to another place, that would be cool, too.



Thanks!

hot_rod

careful

with those wood fireplace heat exchangers. if ever you had a power outage or failed control or pump they can flash to steam and crete a potentially dangerous condition. small water content, with a fire that doesn't stop quickly= problems.



Back in the day there were some of those manufactured for fireplace use. HydroHearth was one brand. I suspect insurance liability was one reason the disappeared from the market.



With wood fired heat sources, ideally you would want a buffer or storage tank. Burn a long hot fire and store the energy until needed. primary secondary piping is one way to tie into the current system.



Not knowing the size of your fireplace i wonder that you would harvest enough energy to make it worth the effort. Maybe a little DHW contribution, probably not a lot of heat load contribution.



A lot of unique wood burner DIYers hang over at hearth.com check the Boiler Room over there for ideas also.



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