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Grow radiant —exploring alternative radiant heating surfaces

Feb. 10, 2014
My long term goal for this property is to say that it is a net zero home I decided to apply a product named Roth Panel It wasn’t designed for application on a ceiling, hence the need for the plywood mounting surface The home is extremely comfortable once it is up and running

As a continuation of last month’s column, we now return to normal programming....

My first major application of a site built radiant panel heating system was at my home in the mountains. I have chronicled this project, known as Hydronicahh, in past issues of CONTRACTOR. My long term goal for this property is to eventually achieve the ability to say that it is a net zero home. I intend to do this using as much alternative energy as possible including solar thermal, solar PV, air source heat pump, and woody biomass. This dictated the need to install the tubing at a relatively higher density compared to a conventional radiant floor heating system.

I decided to apply a product that was originally designed for radiant floor heating applications. The product is made by a company called Roth and is named Roth Panel. This required me to install a layer of ½-in. plywood on the ceiling to give me a good mounting surface for the radiant panels. The physical panels were 2-ft. X 4-ft. with preformed aluminum sheet attached with adhesive to ¾-in. expanded polystyrene foam on the backing. 

To continue the discussion about alternative radiant systems, go to our new Plumbing Talk forum.

As I stated, it wasn’t designed for application on a ceiling, hence the need for the plywood mounting surface. I over compensated for the improper ceiling application by installing the foam/aluminum skinned panels onto the ceiling by using 1-in. screws with large 1-1/4-in.  fender washers with an 1/8-in. hole in the center. I screwed the panels on a 6-in. center to insure excellent contact and retention. I then pushed the ½-in. PEX tubing into the 6-in. on center grooves using a special “tool” that I had developed to insure proper seating of the tubing into the preformed grooves in the aluminum receiver.

Although it technically was not necessary to completely cover every square foot of the ceiling surface to achieve thermal equilibrium with my modulating condensing boiler, knowing that the solar thermal system would only deliver 120°F fluid temperatures during the winter months, I decided that overkill was the best measure. I then covered this final heat emitting surface with a ¾-in. covering of sheet rock, and then the final finish material was an additional ¾-in. covering of sheet rock. My reasoning for doing this double sheetrock was to give me a good place to “park” the Btus that would be coming from my alternative energy sources, primarily my solar thermal system.

During the week days, when I reside in town, my solar thermal system delivers all of its energy to the ceiling. By having this much mass in the system, it helps to stabilize the room temperatures, and keeps my home toasty warm in its set back temperature, which is 40°F when I am not there. When we are there, I crank the room temperature up to around 68°F. Fortunately for me, I can do this temperature change remotely via the Internet. It takes roughly one to three days depending upon the time of the year and the temperatures outside to get the house out of unoccupied set back and back up to the occupied comfort mode.

If I had to wait until I was physically there before I could turn the temperature up, it would not work satisfactorily. By the time the home finally got comfortable, it would be time to leave and head back to the city. This is a real common problem for occasional-use homes up here in the mountains of Colorado, and worthy of an article in and of itself in the future. Back to my project … once the system is completely recharged, it takes very little energy to maintain it in the comfort mode.

The home is extremely comfortable once it is up and running. In fact, one of the features that I really love is that when it gets real cold outside, I can feel the heat emitting from the ceiling, and it feels like basking in the sun. The other wonderful feature is that the floor is actually not cold to the touch, but is rather comfortable (like 74°F) when the ceiling is running. I can cover my floor with bear rugs if I want because it isn’t the heat emitter, but rather the heat absorber/re-emitter.

Today, there are many more radiant ceiling systems available that are actually designed for application on ceilings and walls, making the job of installation much simpler, quicker and easier than doing a radiant floor. As I have said in previous articles, I truly believe that this methodology is one of the most overlooked opportunities as it pertains to not only new construction, but more importantly, retrofit considerations.

In most cases, it may not be necessary to cover every square foot of ceiling with the heat emitter in order to deliver excellent comfort. Run the numbers, and see where it comes in, and I think that you will be pleasantly surprised to find that a 4-ft. band around the exterior perimeter is more than adequate to carry the load. Remember, a radiant ceiling can put out more energy per square foot than a radiant floor, because we are not physically in touch with it.

Tune in next month as we continue looking at alternative radiant heating surfaces in our efforts to “Grow Radiant.” If you have not yet become a member of the new RPA, by all means go to our website at and sign up. It is an inexpensive way to support your industry, which is here to support you!

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