While visiting a friend who has an OWF, he complained to me about having to open a window because it got too hot on the house. Having an OWF myself, and thinking I knew a thing or two, I figured that I could make a suggestion for him.
After hearing his explanation (not needing the blower in the relative warmer times of burning), it became obvious to me that merely the circulation of the water from the OWF pump through the crawl space and air/water heat exchanger in his ductwork radiated heat into the home. While this is to me a substandard installation, allowing too much heat to escape by not being insulated properly (and causing more wood than necessary to be burned), he is a sensitive sort and would not respond well to the suggestion that it wasn't installed properly.
It is my idea to suggest to him a three-way valve to be installed at the pex entry point at the crawl space. This valve would be operated from a signal from the thermostat inside the house which operates the blower. When the thermostat is happy an the blower is not running, have it signal this three-way valve to bypass the house loop and return the flow back to the OWF.
My questions are: 1. What is the proper valve for this? and 2. Any other suggestions? I don't wish to suggest interrupting power to the pump. For several reasons.