I'm planning to add an outdoor gasification boiler to my existing radiant floor heating system. The boiler as well as a ~500 gallon thermal storage tank will be open/non-pressurized. I was planning to use a coil in tank heat exchanger (large coil of copper near the top of tank) to get heat from the storage tank into the closed/pressurized heating system. In this configuration the load could never pull heat directly from the boiler, it will only work after the boiler has brought the tank up to a usable temperature. My concern is that the first 4-6 hours of firing will be used just to bring the tank temp up with no heat output to the load. I guess this is just a problem for the first firing of the season and I shouldn't be concerned about it? Is there a better way to implement unpressurized storage with a pressurized heating system? I'm not opposed to using plate heat exhangers. I'm looking for any suggestions to improve performance and/or efficiency.
![[Hearth.com] OWB with open storage, draw from boiler?](https://www.hearth.com/talk/attachments/img_20260427_085308039-webp.347527/ "[Hearth.com] OWB with open storage, draw from boiler?")
OWB with open storage, draw from boiler?
- Thread starter Rockcrawl
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Most OWB are not designed to use storage. What did the OWB manufacturer say when you asked them about adding storage? My OWB's runs great without it, and I use very little wood. I'd spend the money on good underground piping, lots of ball valves, and a Grundfos pump.
I have a unpressurized system and in the storage tank there is a baffle that traps the hot water from the rest of the tank and gives heat to the heat exchanger within a half hour of firing the boiler !
I haven't purchased a boiler or chosen a manufacturer yet, just planning.
I've been reading a lot about the European method of batch burning, I think this is better suited to my situation vs burning on demand and idling. My heating load is quite low, even a small wood boiler will spend a lot of time idling. I'm afraid it will idle long enough between firings that it will require constant relighting. I'd rather load and light once per day or perhaps every second or third day in the swing seasons, burn hot and continuous, and store the heat. It seems like everyone who has a wood boiler with storage only seems to want more storage capacity.
hobbyheater, I'd like to see a drawing or diagram of your tank if possible.
I've been reading a lot about the European method of batch burning, I think this is better suited to my situation vs burning on demand and idling. My heating load is quite low, even a small wood boiler will spend a lot of time idling. I'm afraid it will idle long enough between firings that it will require constant relighting. I'd rather load and light once per day or perhaps every second or third day in the swing seasons, burn hot and continuous, and store the heat. It seems like everyone who has a wood boiler with storage only seems to want more storage capacity.
hobbyheater, I'd like to see a drawing or diagram of your tank if possible.
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