Most hydronic systems have the boiler running up to 180° F with water returning from the system at 160°. This rarely happens in real life, but it’s the traditional way we do things.
In 2012 the price of #2 fuel oil in upstate New York was approaching a previously unheard of $4 per gallon. This spurred many pending heating system projects to consider the use of cordwood or wood pellets.
If you’re my age, you’ll remember Chubby Checker singing the Limbo song. If you’re wondering who and what that is, check out the link. I found myself thinking of that song and how low can you go when reviewing some flat panel radiator pictures.
As with most things hydronic, there are multiple approaches, and the “best” approach for each installation has to consider cost, aesthetics, access to the existing piping, available wall space and the goal of how the overall system will operate based on existing or newly created zones.
One of the best things about hydronic heating systems is that it’s easy to integrate some method of domestic water heating. This combination has been used for decades in systems where a boiler was the sole heat source. It’s also possible when a heat pump serves as the heat source.
Ask a professional engineer about the energy used by the heating systems they design. Their response is almost guaranteed to apply to the “fuel” energy (e.g., natural, gas, propane, oil, pellets, etc.) used by the system’s heat source(s).
I’ve written several “Heating with Renewable Energy ”columns covering the benefits of combining modern hydronics technology with modern air-to-water heat pumps.