A New Homeowners guide to using radiant heating...

Mark Eatherton

To the consumers out there, enjoy. To the contractors out there, please feel free to distribute to your new, and even existing customer base.


A Consumers Guide to Radiant Heating PART 1

Congratulations! You now have one of the most comfortable heating systems in the world. Radiant heating dates back to before the birth of Christ. It’s roots have been traced back to Korea and were being used for delivering radiant comfort in a system called Ondol. Back then, they used a series of tunnels with a wood burning hearth at the inlet to the tunnel. The smoke from the fire wafted though tunnels constructed immediately below the homes floor. The hot smoke transferred its heat through the stone floor to help heat the home. The smoke eventually rose up through a chimney and exited the home.

Your new radiant heating system does the same thing except that instead of smoke, warm water is circulated and instead of tunnels your system uses tubing that is imbedded in the floors of the home.

This method delivers radiant heat, which can be more comfortable than a typical forced air convection system, however there are some very important factors that new users of radiant heating need to be made aware of in order to guarantee an excellent radiant comfort experience.

What is Radiant Heating and how does it work? Radiant heating heats mass, and not air. Air temperatures can be influenced by the radiant heating system, however the goal of a radiant heating system is to raise the temperature of those surfaces surrounding your body so that your body loses less heat to the environment. In engineering speak, it is known as the Mean Radiant Temperature, shortened to MRT. Our average exposed skin temperature is 85 degrees F. In fact we have around 20,000 temperature sensors covering our bodies. These sensors are extremely accurate and can detect temperature variations as small as 1/2 degree Fahrenheit. They can also detect variations in the MRT.

Can I use a programmable thermostat with my radiant heating system? No and Yes. Radiant heating system in general are not conducive to deep nightly set backs and quick reasonable recovery. Due to the fact that it heats mass first, and air secondarily it is not recommended that most common use areas be subjected to daily deep set backs and recovery using a programmable set back thermostat. Most well built homes lose very little heat from the time the thermostat is turned down, and the rate of recovery is so slow, that the intelligent thermostats will eventually stop setting themselves back resulting in little to no energy savings associated with the programmable thermostat.

In fact, in many cases, the fluctuations in MRT and air temperature when the system is recovering will cause a lot of discomfort due to temperature overshoot. By the time the thermostat decides that it has had enough heat and turns off its call for heat, there is still a significant amount of energy that has yet to come into the room from the mass intensive floor, and this incoming excess energy causes the overshoot of room temperatures and excessively warm temperatures. The overshoot condition can actually create temporary discomfort instead of comfort.

The one exception to this programmable set back rule is bathing areas. In these situations, the use of a programmable thermostat will cause the floor to raise its temperature temporarily which feels great for people who are poorly clothed (naked) and wet.

It is suggested that this bathing room be allowed to lose a few degrees overnight, and that it be programmed to recover 2 hours before first use in the morning. So, if you usually shower at 6:00 AM, then you want to start recovering the heat at 4:00 AM. This way, when you walk into the bathroom, the floor will be warm and toasty. You can then program the room temperature to reduce its setting when the last person is done using the bathing facilities. Keeping the bathing environment at a constant high heat setting all the time will result in what is referred to as “Overdrive and Thermal Creep”. Heat always flows from a warmer environment to a cooler environment. If you keep your bathing area at a constant 74 degrees F. and you would like to keep your attached sleeping area at 65 degrees F., the higher temperature being maintained in the bathing area may cause the sleeping area to stay warmer than 65 degrees F. If you have a door between the sleeping area and the bathing area, closing this door can help lessen the effects of the constantly warm bathroom. Recommended settings for a bathroom programmable thermostat would be to maintain 69 degrees F during “Away” or “Sleep” periods, and 72 degrees F for periods of time that the bathroom will be used for bathing ”Wake” and “Return” or “Occupied” periods. As previously mentioned, have the thermostat turn the temperature up at least 2 hours before first use in the morning (or evening), and turn it down after the last use in the morning (or evening).

Mark Eatherton

Part 2

This will lessen the thermal creep to adjoining spaces associated with keeping the bathroom warm all the time and still provide a warm floor experience first thing in the morning or evenings when being used for showering and or bathing.

What about other common use areas? Again, due to the nature of radiant heating systems being slow in recovery, it is not recommended that programmable thermostats be used for these areas. As for a recommended constant temperature setting, for first time users of radiant heat, it is recommended that you “Start Low and go up SLOW”. Start the temperature setting somewhere between 65 and 68 degrees F. Allow the living space to stabilize for at least 24 hours before making any adjustments. When making the temperature setting adjustments, don’t raise the room temperature by more than 1 degree F., and again, allow the room to sit for 24 hours before making any further adjustment. Once you find your “Comfort Zone” for that space and that use, it is suggested that turning the temperature back one degree F., and again, allow the mass to stabilize for at least 24 hours before making further adjustments.

The biggest complaint from first time radiant users is discomfort due to over temperature conditions, hence the recommendation to turn it back by one degree once your comfort zone is found. MRT is the primary factor that determines good human comfort, followed closely by air temperature. Having too high of an MRT will result in discomfort due to the higher MRT which can’t be sensed by sensors, but is felt by the humans within the space.

As it pertains to the different space usage, the correct temperature for a given area is dependent upon many factors, including the quantity and orientation of highly glazed (glass) areas, physical activity (or the lack of), clothiness and location in relationship to outside walls. If you have an exercise facility that is internally located, you may want to turn the temperature to around 60 degrees F. The room may never cool down to 60 degrees F, but if it is cold, the coolest it could get would be 60 degrees F. In the case of a highly glazed area, with a poorly clothed person who is sedentary, you may have to turn the room temperature to as high as 72 degrees F in order to achieve good comfort. Due to variations in metabolism, finding the perfect temperature for all parties concerned may pose a challenge.

It is also important to understand the difference between “warm floors” and “radiant comfort”. In many cases, until it gets fairly cold outside, most floors will not be “warm” to the touch. In general, you will be very comfortable due to the radiant comfort being delivered, but the floors will not neccessarily be “warm” to the human touch all the time.

What about “occasional use” rooms? Occasional use rooms describes rooms that are not regularly used for extended periods of time. As an example, a spare guest bedroom, an away at college students bedroom or a large formal seasonal use dining room meets that description. In these situations, it is acceptable to keep the room temperature turned as low as 60 to 65 degrees F. If there is no door between this space and a regularly conditioned space, then little room air temperature deviation will be experienced. In the case of the dining facilities, it is recommended that if there will be many people in the room, that the room temperature not be turned up. The room will be heated quite well when the people and heated food enter the room. In fact, it may become necessary to provide cooling in order to keep this space from overheating.

Should I keep my thermostat set for Auto, On or Off?: If the thermostat is responsible for also doing cooling in a given zone, it should be set for auto. Thermostats should never be placed in the “OFF” position. If you happen to forget that you left it in the off position, and the room cools way down, when you turn the thermostat back on, the room will most probably over shoot its set point. Keep the thermostat in the ON position (or auto if doing cooling) and keep it turned down if you don’t want or need a lot of heat in that area. This will avoid the over cooling and then over heating associated with the system attempting to recover from a cold start.

I like to keep my window open at night. Can I do that with radiant heat?: Yes, but if you like a cooler sleeping environment, it is suggested that you keep the bedroom thermostat turned down. Otherwise, when the room thermostat senses the cool air coming into the room, it will start the heating system in an effort to maintain a higher room temperature. Remember, turn it down, but not off, and don’t forget to close the window in the morning so that cool air doesn’t infiltrate through the home and cause other zones to heat up.

In general, radiant heating and cooling provide a much higher degree of human comfort than a conventional convective or forced air system. It just takes a little getting used to, but once you do, you will discover that this method of providing comfort is far superior to anything you’ve ever experienced.

To recap, avoid major temperature changes in thermostat settings. With the exception of bathing areas, avoid the use of programmed set back and recovery periods. If you will be leaving the home empty for a long period of time (weeks as opposed to days) you can turn all thermostats to a lower setting to save energy, but make certain that someone turns the thermostats up a couple of days in advanced of your returning home to ensure thermal mass stability and associated comfort upon your return.

Lastly and most importantly, Enjoy!