How do I know if my outdoor wood boiler is an open system?

Of course your manufacture would be the first resource. But if it requires intermittent filling due to water evaporating from the vessel, or if there is a vent on top of the outdoor wood boiler, these are very strong indications. (See the image below)

About 95% of all outdoor wood boilers are in fact open systems.

This would include: Central Boiler, HeatMaster, Hawken, Natures Comfort, Earth Outdoor, Hardy, Polar, Portage & Main, WoodMaster, Crown Royal, Ridgewood, Tenessee, and many others.

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