“You can go almost anywhere now and buy radiant heating hardware — tubing and manifolds and other components — and there are many places that sell it online, so the availability of the hardware is not an issue, and literally anybody can get it,” says John Siegenthaler, principal of Appropriate Designs in Holland Patent, New York City, and a Hydronics Zone columnist for The NEWS. “That’s both good and bad. It’s good that it’s not difficult to get the hardware, but it allows people who don’t really have any background to go ahead and try to do their own home-brewed installations, and sometimes the results aren’t very good.”

To help improve the quality of radiant installations nationwide, Radiant Professionals Alliance helped develop a voluntary consensus standard to provide minimum requirements for installers and designers of hydronic heating and cooling systems and installers of solar water heaters. ASSE/IAPMO/ANSI Series 19000-2015, “Hydronic Systems Professional Qualifications Standard,” provides minimum requirements for installers and designers of hydronic heating/cooling systems and installers of solar water heaters. 

“What they need to do with any model code is convince municipalities that may be interested to adopt it,” Siegenthaler says. “It is a good thing, if they can get that out there. It sets some legal standards once it becomes part of the code and is the law. That’s going to improve installations and should help stop some of the really bad design practices that are out there.”

 The standard will help give credibility to radiant installers, though it will be up to the industry to support the program, says Dan Holohan, operator of HeatingHelp.com and a Hydronics Zone columnist for The NEWS.

“The standards are in place, and it’s done; now, it’s just a matter now of promoting this non-mandatory standard, and that has to be done by businesses,” Holohan says. “As people get certified, they’ll start getting more certified, and maybe that will get others to be certified, too. These tests are not easy.”

Farewell to Fossil Fuels?

The biggest trend in radiant is not how the thermal energy is transferred, but where that energy is coming from. Industry leaders predict traditional high-temperature fossil-fuel boilers are going to give way to electric systems, including lower-temperature air-to-water heat pumps; additionally, heat recovery and renewables are going to play a much bigger role in radiant heating and cooling.

“We have to start thinking about other ways of heating that water in the hydronic systems, because boilers are going to become obsolete,” says Jim Godbout, owner of Portland, Maine-based Jim Godbout Plumbing, Heating, and Air Conditioning, a diverse enterprise that tends to cater to high-end residential contracting. Electric boilers are an affordable option in certain areas, he adds. “That’s an efficient way, if you can buy electricity cheaply. In New Brunswick, Canada, electricity is about a quarter of the cost of here in Maine, so they use that for their hydronic systems.”

But the most significant shift right now is the move toward air-to-water heat pumps in lower-temperature hydronics installations, including radiant. “It’s already started in the European and Asian markets, where the trend now is to use more air-to-water heat pumps,” Godbout says.

“I think there’s some truth to that,” Holohan agrees. “They’re looking at other ways of making the water warm, and the water doesn’t have to be super-hot for radiant heating.”

There are about 1.7 million residential-sized air-to-water heat pump units in Asia and Europe, Siegenthaler says, though it has not quite caught on in the U.S. — yet.

Air-to-water heat pumps are a new and very viable heat source to tie into low-temperature hydronics, like radiant panels and low-temperature baseboards, Siegenthaler says. And, in the summer, it can produce chilled water for cooling.

“With this system, it has an outdoor unit just like you’d see with a standard a/c system that sits outside on a pad, and then you have tubing and electric going into the building. The difference is that on the inside, you’re delivering the heating or cooling with hydronics,” he says. “Imagine it producing a stream of water at 45-50^°F, which would circulate through a wall-mounted air handler, like with ductless mini-split systems, but instead of having refrigerant going into it, it has chilled water. It can be a very efficient cooling system, and you can zone it. It’s hydronic-based cooling using a heat pump.”

“We’ve done it in half a dozen locations right now over the past year and a half,” Godbout says. “So far, so good.”

It also has cost advantages, especially when compared with similarly efficient technologies. In a highly efficient home, for example, the energy costs of operating a geothermal heat pump tied to a forced-air system can be on par with an air-to-water heat pump operating a radiant heating and cooling system.

“You can install an air-to-water heat pump system for one-third to half the cost of a geothermal system, and that is with the 30 percent geothermal tax credit that is expiring at the end of the year,” Siegenthaler explains. “When you combine air-to-water heat pump technology with low-energy-use houses, like a home approaching net-zero, what happens is the performance of the geothermal system on a seasonal basis might produce less than $100 difference in savings over the heat pump. Now you’re trying to amortize a difference in installation costs of $6,000 to $10,000 for $100 a year in savings over the heat pump system, and it just doesn’t make sense.”

Designing for the Future

With the prospect of a major shift toward lower-temperature heat sources on the horizon, installers are going to have to start being much more conscientious about how they design hydronic systems. Additionally, renewables, thermal energy storage and heat recovery are all going to play a much larger role in hydronics.

For example, in Sweden and France, some developers have found ways to harness body heat as a source for radiant heating systems in nearby buildings. “The Stockholm train station and the Paris Metro are both collecting the body heat of the people moving through the station — people giving up Btu,” Holohan says. “Normally, it’d just be exhausted, but they’re able to capture the body heat and put it into water for heating apartment buildings nearby radiantly.”

Another example of utilizing body heat for free heating is the Mall of America in Bloomington, Minnesota, where the halls of the massive structure aren’t heated at all, Holohan says. “Individual stores have heating, but the mall itself, it’s heated by people. Everybody is walking around and moving and heating the building.”

The heat from the sun is also being harnessed and then stored for later use, by using the Earth itself as a heat sink, Holohan adds.

“Developers put solar thermal panels all over the place and drill bore holes like they were doing ground-source geothermal. In the summer, the heat from the sun makes the ground hot a few hundred feet down. Then, when it gets cold, they tap that heat for radiant heating,” he says. “This also applies to district heating. There are subdivisions in the Carolinas where they put solar panels on everyone’s house, and there’s a district system that moves the water through pipes, and they all draw on it in the winter.”

“You can see the world trends are getting away from boilers,” Godbout says. “There’s always change in the world. I still believe hydronics is going to play an important part in people’s comfort and heating and cooling their homes. I don’t think it’s going to go away — we just need to find a new delivery device.”

With so many changes occurring in hydronics lately, it’s more important than ever to ensure new hydronic distribution systems are able to accommodate new technologies.

“I look at it this way,” Siegenthaler says. “If you do a good job putting in a hydronic distribution system, it should last for decades. You could even make good arguments for 100 years if it’s properly designed. I call it future-proofing your distribution system. Over that period of time, it’s going to see multiple heat sources. You might put a new modulating/condensing boiler on it initially, and that boiler might last anywhere from 15 to 20 years, and then it’s going to have to be replaced. Today, if we design it around high water temperatures, then 20 years from now, we don’t know what those heat sources could be. There could be a very strong market for heat pumps; it could be solar. But here’s the bet I’m telling people to make: Whatever that future heat source is, it’s going to operate better at lower water temperatures.

“I think of heat pumps, in particular, as meeting that,” Siegenthaler continues. “They just don’t produce 180 to 190 degree water — they produce 120 degree water. So what I tell people is, design today for what the future is going to be. Future-proof the distribution system. What that does is keep those future options open for you, so that if that initial boiler dies after 20 years and you need to replace it, maybe with an air-to-water or geothermal heat pump, it can tie right into that distribution system and not require you to do major surgery inside the house as far as changing the distribution system around.”