Controlling radiant comfort systems

Dec. 9, 2014
Options for individual zone control have changed significantly over the past 10 years. Radiant delivery systems fall into one of two categories: high mass and low mass.

Now that we have covered just about every type of radiant panel ever known to mankind – and a few that weren’t – in my past columns, it’s time to move on and discuss some more juicy details about these wonderful comfort delivery systems. This includes things like how to control them, which heating/cooling sources are available and so forth. I’d like to start the conversation about controlling these comfort machines.

Our options for individual zone control have changed significantly over the past 10 years. It seems as though the Internet has become an integral part of our lives, and it is an important part of delivering the comfort expectations of the new consumers. These Internet controls are not for everyone.

Your grandparents may have discovered Facebook, but there’s a good chance they have yet to master the state-of-the-art smartphone technologies necessary for complete and total access to their comfort system.

Fortunately, a person still may purchase a conventional wall-mounted thermostat to meet this need. Before we delve too far into this subject, I think it is important to clarify the application of programmable set-back thermostats as it pertains to radiant heating and cooling systems.

Radiant delivery systems basically fall into one of two categories. Those categories are high mass or low mass. It has been stated before that high mass systems are simply not conducive to deep set backs, and that statement remains true. If you have tube-in concrete or other mass intensive panels, the mass will not cool down quickly, nor will it recover quickly.

It’s the nature of the beast, and it is not recommended for daily deep set backs and recovery periods. Oh sure, you can knock off a few degrees Fahrenheit at night, and recover that fairly quickly in the morning with enough head start, but do not expect to be able to drop 10°F at night, and recover the room temperatures within a reasonable period of time.

As for long-term setbacks – like when you go on vacation – yes, it is a good idea to turn the set point of the home down, within reason. More importantly, though, it is necessary to turn the temperature back up days before your expected return from vacation.

Obviously, this is going to require someone entering your home to do this. If you don’t have that ability, expect coolish conditions for a few days after your return. Remember, radiant primarily heats mass, not air, and if all that mass is cooler than the surrounding air, then your body will feel the cooler surroundings until they are recharged with thermal energy.

Even a low mass system under these conditions may need a few days to get the internal mass recharged to a comfortable level. Here in Colorado, radiant heating systems have gotten themselves a bad name due to its application in “second homes” and “vacation homes” in the ski resorts.

This is due to the fact that when their occasional-use home is unoccupied, they turn the thermostats to a very low set point of between 40°F and 50°F. When they show up Friday night, the home and all of its internal mass has cooled off, and it takes days to warm up to the point that heat can be sensed. The home typically gets to a comfortable level just about the time they are ready to go back home Sunday night; hence the reason radiant has gotten such a bad shake in this market.

In reality, even if the home were heated with forced air they still wouldn’t be comfortable until Sunday night, but there is something comforting about having warm air blowing across your skin. It gives the perception that you are warm. This remote occasional-use home situation is an ideal application for one of the many Internet-connected thermostats. The owner can turn the home up remotely from anywhere in the world with Internet connectivity, and by the time he or she shows up to go skiing, the home is at a perfect temperature.

But I digress. We were talking about the difference in high versus low mass heat-emitting surfaces and applications with set-back controls. A low mass system, be it panel radiators on walls or ceilings, or integrated radiant walls or ceilings, are conducive to a deep set back and quick recovery on a daily basis.

It has been my personal experience, though, that if your home does cool down by 10°F to 15°F overnight, you’d probably be wise to grab a caulk gun and try to plug off some of the excess infiltration that is causing your home to cool down so quickly over such a short period of time.

In any case, a low mass radiant panel (floors, ceiling, walls and countertops) is very fast to react and deliver warmth back into a given space. Personally, before I even begin talking about thermostats with the consumer, I try and have a discussion about how many zones they should have, and how those zones are split up. At a minimum,I recommend three sub zones.

Those zones are sleeping areas, common living spaces (living room, kitchen, etc.) and uncommon living spaces (formal dining room, library, exercise rooms, etc.). If the consumer wishes to control each room individually, it is technically possible, but it comes with additional expenses.

Tune in next month as I help you continue to evaluate your options in delivering good radiant comfort from alternative surfaces. Next up, Part Two of “How Do We Control These Wonderful Systems?” The RPA will be giving a class on state-of-the-art, PC-based Internet control systems at the AHR show. Get more information at

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Mark Eatherton

Mark Eatherton material on this website is protected by Copyright 2017. Any reuse of this material (print or electronic) must first have the expressed written permission of Mark Eatherton and CONTRACTOR Magazine. 

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