Heat pumps offer attractive solutions to energy-efficient heating and cooling, and the market is growing. According to a November 2021 report from the International Energy Agency (IEA), nearly 180 million heat pumps were used for heating in 2020, as the global stock increased nearly 10% per year over the past five years.

The report notes that though some of those heat pumps only partially cover space and water heating needs, growth is still evident across all primary heating markets, including North America, Europe and Northern Asia. The report also acknowledges that heat pumps have become the most common technology in newly built houses in many countries, but still only meet 7% of global heating demand. “In the United States, for example, the share of heat pump sales for newly constructed buildings exceeds 40% for single-family dwellings and is near 50% for new multi-family buildings.”

Therefore, heat pumps have become a hot topic for TV shows like PBS’ “Ask This Hold House.” The series has actually covered heat pumps quite a bit, with the latest being its “Understanding Heat Pumps” episode as part of the Future House segment this past January. The show covered the four different categories of heat pumps, including water-to-water, water-to-air, air-to-air and air-to-water.

If you saw the episode, you may have recognized a familiar face — one other than Rich Trethewey. That’s right, PM Engineer’s very own John Siegenthaler made a guest appearance. Check out the video clip below. Siegenthaler appears at about 4:23 minute mark, though the whole video is worth a watch! PM Engineer sat down with Siegenthaler to discuss his experience on the hit show, as well as the buzz surrounding air-to-water heat pumps. 

PM Engineer: How did you come to be on an episode of “Ask This Old House?”

JS: I’ve known Rich and Ross Trethewey from the show for several years. Ross has been doing segments on other types of heat pump systems, and I speculated that he would be interested in covering the relatively new air-to-water heat pump configuration. As the tech expert on the show, as well as a licensed mechanical engineer, he was very interested, and pitched the concept to the show’s producers.  After that it all fell into place for shooting last June.

PM Engineer: What was filming the episode like? How long did it take?

JS: The filming was a lot of fun, as well as a unique opportunity to see the equipment and staff that are all ‘behind-the-scenes’ in the finished segments. There were a crew of five people including Ross. They spent most of the day shooting (and reshooting) segments often based on seemingly minor details like changing lighting due to clouds, or even minor background sounds. I was amazed at the crew’s awareness of all these details and how they adapted to them. Also interesting to see how all the on-site shooting ‘boils down’ to a few smoothly-connected minutes of the show.

PM Engineer: Whose house was featured in the episode? Was it a client?

JS: The heat pump was being installed at my son Chris’s house near Albany, New York. The installation was done by “The Radiant Store” in Troy, New York. Ben Melick, was the principal technician, and Terry Moag, the company owner. They did a meticulous “textbook example” installation.

PM Engineer: Why did your son decide to install an air-to-water heat pump system?

JS: When I found out how much propane was costing the young family, I pushed to do a heat pump retrofit.

PM Engineer: Why are air-to-water heat pump systems good to use in retrofit projects like the one shown on the show?

JS: For several reasons: No. 1: They displace what in this case was very expensive fossil fuel ($4.40 per gallon for propane), saving the family over $2,000 per year. No. 2: They are a complete solution to space heating, cooling and domestic water heating. No. 3: They allowed an existing forced air distribution system to be reconfigured to allow future expansion using panel radiators or towel warmers.

PM Engineer: Are there any limitations in using this type of system in a retrofit?

JS: The chief limitation is the water temperature that the existing system requires at design load conditions. On older higher temperature systems that might need 180° F water at design load, the air-to-water heat pump can likely displace 70% to 80% of the fossil fuel requirement. On lower temperature systems that might only need 120° F water at design load, the same heat pump can likely displace 95%  or more of the fossil fuel requirement.

PM Engineer: What are the benefits of replacing a forced air/fossil fuel system with an air-to-water heat pump?

JS: In this case, significantly lower operating cost, and the ability to expand the system using hydronic heat emitters. This system also switched the domestic water heating requirement from propane to heat pump.

PM Engineer: Are these systems becoming more popular in the U.S.? Why or why not?

JS: The market for air-to-water heat pumps is continuing to expand in the U.S. More manufacturers and products enter the market each year. The overall efficiency of a typical air-to-water heat pump in a cold climate is not quite as high as that of a geothermal heat pump. However, the installation cost is typically 30% to 50% of that of the geothermal system. This makes the return on investment attractive, especially in situations where the geothermal heat pump is not be subsidized. There’s also no need for excavation and site disruption using the air-to-water heat pump, which makes them applicable to a higher percentage of homes and commercial buildings.

PM Engineer: Where do you see the air-to-water heat pump market heading in the next five years?

JS: I expect continued growth in the air to water heat pump market in the years ahead. More products to choose from, many of which are suitable to cold climate applications. The key concept is the “marriage” of the efficiency of modern air source heat pump technology with the superior comfort of a properly designed modern hydronic distribution system. Another key concept is that the heat pump can provide a total solution in terms of space heating, cooling, and domestic hot water. I’ll definitely keep PM Engineer readers posted as air to water heat pumps gain market share in the years ahead.