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 covered pellet-fueled boiler applications in several past issues of PME. All of them have involved hydronic distribution systems. While such applications are certainly the prevailing way pellet boilers are used, they are not the only option. It’s possible to couple a pellet boiler to a forced air distribution system.

I’ve written several “Heating with Renewable Energy ”columns covering the benefits of combining modern hydronics technology with modern air-to-water heat pumps.

All hydronic systems designed around renewable energy heat sources — as well as those designed around conventional boilers — have at least one controller that measures and responds to temperature. Common examples are temperature setpoint controllers, outdoor reset controllers, mixing controllers and differential temperature controllers. Complex systems that operate in multiple modes, or use multiple heat sources, often have several temperature-based controllers.

As global energy planning moves away from fossil fuels and toward electricity, an increasing number of hydronic heating systems are being supplied by heat pumps. Some use water-to-water heat pumps supplied by geothermal earth loops. Others use air-to-water heat pumps.

Heated floor slabs, without floor coverings, have one of the lowest supply water temperature requirements of any radiant panel system. This makes them well-suited for use with renewable energy heat sources such as air-to-water heat pumps, water-to-water geothermal heat pumps, biomass boilers and solar thermal collectors.

On the older hydronic systems, replacing the existing boiler with a new one was pretty straightforward. The installer connected the new boiler to the existing flue, piping and electric. The newer high-efficiency boilers are much different and require some additional planning.

Heat pumps move heat from low-temperature sources to higher temperature loads. There are many types of heat pumps, but they all perform this basic thermodynamic mission.

Even though PEX has a long history in construction applications, its early North American beginnings in residential radiant floor heating systems more than 35 years ago dubbed it a “residential” product for the first decade or so.