More and more hydronic heating and cooling systems are being designed around air-to-water and water-to-water (geothermal) heat pumps. When the heating distribution system is extensively zoned, a buffer tank is typically installed between the heat pump and that distribution system.

When designing hydronic circuits, most engineers focus on what’s necessary for that circuit to absorb thermal energy at a heat source, carry it along like a conveyor belt and drop it off at one or more heat emitters.

Government planners, taking their queues from politicians and advocacy organizations, have steered the future of energy supply away from fossil fuels and toward renewably-sourced electricity. It’s happening on every level from the feds right down to local city councils.

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.

Many legacy hydronic heating systems use a fossil fuel boiler to supply fin-tube baseboard heat emitters in some areas of a building and lower-temperature radiant panels in other areas. 

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.

Although I’ve worked with hydronic heating for four decades and designed systems around just about every possible heat source, I would be hard-pressed to predict what might be available as hydronic heat sources 25 years from now. 

What characteristic do solar thermal collectors, hydronic heat pumps and thermal storage tanks supplied by biomass boilers have in common?

Water-to-water heat pumps, supplied from geothermal earth loops, represent a growing sector of the hydronic heat source market. Most current-generation models can produce water temperatures up to about 125° F, perhaps a little higher if you’re willing to push the compressor operating envelope.

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.