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. 

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. 

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.

 All boilers that burn hydrocarbon fuels such as natural gas, propane, oil or wood produce water vapor as a byproduct of combustion.

I’ve written it before and I’ll write it again — panel radiators are one of my favorite hydronic heat emitters. I base this sentiment on several benefits. Here are a few to consider…

The choice between ∆T and ∆P operation of a circulator has, at times, been the subject of rather “heated” debates. It’s almost as if a few Yankee fans are disputing superior pitching or batting performance with a few Red Sox fans. There appears to be some strong opinions involved.

As building codes and programs such as Energy Star and Passive House require higher degrees of air sealing in new construction, the use of heat recovery ventilation (HRV) is increasing.

Nearly all closed-loop hydronic heating and cooling systems are supposed to be filled with water or a mixture of water and antifreeze. The only intentional air in the system is that contained in the expansion tank.

As residential building codes and energy conservation standards continue to evolve, many are requiring proof of high quality air sealing.

Over the last few years, I’ve written several columns describing how air-to-water heat pumps can provide heating, cooling and domestic hot water for homes. Many of the systems involve buffer tanks to help stabilize heat transfer from the heat pump to a zoned distribution system.