As the old saying goes, there is more than one way to skin a cat. The same can be said of residential hydronic systems, which can be designed around numerous types of terminal units, including baseboards, radiators, air handlers, and radiant panels, to name just a few. Deciding which type of unit will work best for an application involves a close examination of several factors, including cost, home construction, aesthetics, and how the system will be used.

Not surprisingly, cost is often the biggest driving factor, especially if the home builder is making the decisions rather than the homeowner. If the contractor is able to work with the homeowners, however, it is possible to dig a little deeper to determine which hydronic heating system will best meet their needs.


Hydronic heating professionals often start off conversations with homeowners by asking, “What do you want to accomplish with this system?” This is not a simple question because it encompasses much more than just keeping the indoor air temperature at 70ºF during the heating season,” noted John Siegenthaler, principal, Appropriate Designs, Holland Patent, New York (see sidebar).

He favors European-style panel radiators because they give off radiant and convective heat, are easy to mount, and can be individually regulated using a non-electric thermostatic valve built into the radiator.

“They cost more than baseboard but significantly less than a radiant panel system,” he said.

But if homeowners are looking for the lowest cost solution, then fin-tube baseboard paired with a cast-iron boiler is typically the best option, according to Siegenthaler.

“To me, the aesthetics of fin-tube baseboard are tolerable but not something most people would choose to have in their home,” he said. “Modern materials such as PEX tubing make it easier and faster to install fin-tube baseboard.”

The lower the water temperature at which a hydronic system operates, the higher the efficiency of its heat source.

“My suggestion is that all hydronic systems should be designed to deliver design load output using supply water temperatures no higher than 120º,” Siegenthaler said.

Dan Foley, president, Foley Mechanical Inc., Lorton, Virginia, said radiant floor heat is the way to go because he believes it is the most comfortable and efficient system available.

“A properly designed radiant floor system can operate at a lower supply water temperature than radiators or baseboard, which is a better match for condensing boilers as well as renewable energy sources, such as solar thermal or geothermal,” he said. “Also, architects, designers, and owners prefer radiant floor heat because there are no visible heat emitters.”

Another fan of radiant heat is Jason Carter, president, Innovative Comfort Systems Inc., Lynnwood, Washington, although most of the homes in his area have oil- or gas-fired boilers paired with radiators.

“We install radiators, baseboards, and air handlers, but I prefer underfloor radiant heat whenever possible because there are fewer moving parts, no noise, and no parts that get in the way of furniture placement,” he said. “Out of sight, out of mind!”

H. Lance Bent, CEO, Melroy Plumbing and Heating Inc., Baltimore, also prefers radiant heat but said he is willing to employ any solution that makes sense in terms of economy, aesthetics, profitability, and optimal performance.

“For historic home restorations, we prefer to match the character and period of the home,” he said. “We like radiant, which can be hidden in older homes, but my personal favorite is the steam vapor system, which is truly remarkable. The problem is that there are too few of us who understand it, let alone repair and design it.”


Home use changes over time, and sometimes an existing hydronic heating system no longer meets the homeowners’ needs. Fortunately, changes can usually be made to the system.

“Some clients prefer the look of radiators over baseboard, and we have replaced baseboard with cast-iron and panel radiators,” said Foley. “It really comes down to piping and access. For example, if the piping is accessible in an unfinished basement, it is easy to switch heat emitters. For a slab-on-grade home, it might be a little more difficult to switch.”

Changing baseboards to radiators is a common request that Carter receives, especially if homeowners want to change the look of their home. He has also been tasked with utilizing several different types of terminal units in one home.

“Water temperatures are easy to manipulate, so multiple types of distribution systems can easily be used in a single home,” he said. “A recent system we did had two hydronic air handlers that were staged with air-source heat pumps, while another area of the house utilized radiant in-slab heat.”

Remodeling often results in changes made to a home’s insulation and ventilation, and this, too, can affect how well the existing hydronic system works. As Bent noted, in the old days, homes were very well ventilated, which required oversized radiation. Renovated homes typically have fewer air leaks and better insulation, but older existing radiators could be significantly oversized for the new heat loss demand.

“When we replace an older, oversized heating unit, we can often replace it with one that is half the size,” said Bent. “Because the radiators are now too big, a choice becomes available. We can leave them there and reduce the temperature of the water, or we can downsize or eliminate some radiators altogether. For people wanting room space, smaller is better. With less heat demand, they can import wall-hung decorator radiators or baseboard. We then calculate the heat loss for the space and make sure the radiation selected meets the demand.”

It is very important to make sure the new radiators are correctly sized according to the surface area of the radiator, said Bent.

“To replace an equivalent square foot cast-iron tube- or column- type radiator that may be 28 inches tall will usually require careful sizing of an equivalent baseboard,” he said. “This will result in a longer unit and require pipe changes, which get expensive.”

Just about any modification can be made to a hydronic heating system, according to Siegenthaler.

“For example, panel radiators can be added to systems with existing baseboard,” he said. “I often recommend a ‘homerun’ distribution system, which is just two runs of ½-inch PEX tubing out to each new radiator. The small flexible tubing is easily routed through framing cavities in buildings and is much easier than dealing with rigid piping.”

Radiant ceilings and radiant wall panels can also be added in selective areas of a house with older heat emitters, such as baseboard or cast-iron radiators, said Siegenthaler.

“Adding floor heating is possible in some situations but impossible in others,” he noted. “It’s highly dependent on what the existing flooring is and how easy it is to access the underside of the floor.

“Adding floor heating in selective areas, such as under tile floors in bathrooms and kitchens, is generally more feasible than adding it to the entire house,” he continued.

Whenever any significant changes are made to a hydronic system, the general rule is to increase the total surface area of the home’s terminal units by using any mix of heat emitters, including baseboard, panel radiators, fan coils, etc., as this will bring down the water temperature requirement, which improves heat source efficiency and comfort, said Siegenthaler.

Unfortunately, too many homeowners do not want to pay for the expertise needed to fix the problems they may have with their existing hydronic systems, because they do not trust it will be done correctly, said Bent.

“We used to build homes and heating systems to last over 100 years, and they were expensive back then,” he said. “Today we are mobile, and no one keeps a home forever, so we build as cheaply as possible. Customers no longer believe or want to pay the real expert, because they have too often been disappointed. We teach that the old dead men who invented this stuff long ago got it right, but we have forgotten their ways.”  

Diving A Little Deeper

When working with a homeowner to decide which type of hydronic system to install, John Siegenthaler, principal, Appropriate Designs, Holland Patent, New York, suggests asking the following questions in order to find the correct solution:

  1. What fuel will be used? Are there any special circumstances, such as off-peak electrical rates, no natural gas service available, etc.? If multiple fuel options are available, what do the clients want to use based on cost, past experience, CO2 emissions, renewable versus fossil fuel, etc.?
  2. Do they want specific zoning in the system? If so, what temperatures do they want to maintain within the different zones?
  3. Do they want the system to produce domestic hot water (DHW) as well as space heating?
  4. Do they want the system to produce cooling as well as space heating?
  5. If they are considering floor heating, what will the finished flooring materials be (high thermal resistance floor coverings generally rule out floorheating)?
  6. How do they plan to have the system maintained? Who do they expect will do this maintenance?
  7. Will there be times when the house is unoccupied for several days or more during winter? If yes, antifreeze solutions should be discussed. Are there times when a large number of people will be in the house? If yes, design the system with low thermal mass to avoid overheating.
  8. Are there any specific health issues for the occupants, such as dust allergies or lowered immune system conditions? Low tolerance to drafts and dust would favor radiant panel heating.
  9. What are their expectations in terms of night temperature setback? Do they want/need fast recovery from significant temperature setbacks? Fast recovery favors systems with low thermal mass heat emitters.
  10. Are there any government incentive programs they could take advantage of? The heating pro should actually be aware of all current incentive programs that would apply and be ready to discuss them, as this could result in significant savings on installation cost.
  11. Are they “techies” who desire wireless access to controls, thermostats, etc., or are they content with simple standard thermostats?
  12. What is their tolerance for system operating noise? If they want total silence, stay away from air handlers, and make sure piping expansion will not create noise.
  13. Looking several years ahead, what’s the likelihood that the house or building will be expanded? Future expansion plans can be incorporated into the initial installation.
  14. Would they be interested in a towel warmer in the master bathroom (who can resist a warm/dry towel)?

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Publication date: 2/19/2018

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