Hydronic Stove Log

Tue Dec 24, 2019

• 1" PEX pipe ruptured right at the stove outlet a year ago from running the stove without the circulating pump in a cleaning operation. The pressure relief did not activate, as the pressure relief was after the PEX pipe, and temperature did not rise much at the pressure relief.
• This is a failure mode that needs to be eliminated by design, such as by using metal pipe and a hot water storage tank on the outlet - though this does not address the inlet side. Another buffer tank would need to added at the inlet side.
• To address the condition where the stove is running without the circulator pump, defusing the heat safely - would be adding a large hot water storage buffer tank. Such a storage buffer would have to be sized so that the heat from any full, hot-burning load could be trapped solely in the volume of the buffer tank. This assumes one load only - as the operator would notice that no house heating is occurring in this fault condition, and the operator would likely not put in another load without correcting the situation.
• Or, a warning light could be added to notify that the circulating pump is not running.
• Automation controls should have a lockout for running the stove without the circulator pump.
• Most redundant control would be a pressure relief valve added to the entrance side and the exit side.
• Current design has the pressure relief after the PEX. The pressure relief should be right on the stove on a metal pipe connection, before any PEX.
• Using PEX is a good safety feature, as any extreme overpressure condition that is not caught by the T/pressure relief valve - ruptures the PEX without causing a life-threatening overpressure condition.
• Outstanding question: is a thermostatic mixing valve desirable on a tankless hydronic stove system? What are the advantages for using such in a house heating application with a wood burning stove?