June 2015


heat the room • BTUH/SF = the room heating load expressed in BTUH per square foot • 2 = the heat transfer coeffi cient of radiant fl oor heating • SPT = the Set Point temperature, or the temperature at which you set the thermostat


John Barba


Contractor Training & Trade Program Manager Taco, Inc.


Radiant Floor


Heating by John Barba


So, do you feel like rolling the dice? Here's a quiz for you...


What’s the easiest way to raise the floor surface tem- perature with a radiant fl oor heating system?


Let’s say the heating load for a 200 square foot room is 4,000 BTU’s per hour. The out- door design temperature is 0 degrees and the indoor design temperature is 70. To deter- mine the BTUH per square foot load, divide 4,000 BTUH by 200 square feet, which is the output requirement for the "radiator" at design condi- tions:


4,000 ÷ 200 = 20 BTUH per square foot.


Next, divide the BTUH/SF heating load by the heat trans- fer coeffi cient of 2:


20 ÷ 2 = 10


New England HVAC Insider


Finally, add the indoor de- sign temperature (70*) used in the heat loss:


10 + 70 = 80


So to heat this room at design conditions, the floor surface temperature - the surface temperature of the radiator itself – needs to be 80*. Doesn't matter whether the finished floor is carpet, hardwood, tile or goatskin, or whether the installation method is slab or aluminum plates - under design condi- tions that fl oor surface needs to be 80 degrees to heat the room up to an air temp of 70 degrees.


Here's a curveball: let's say


it’s only 35* out. That would cut the BTUH/SF heating load in half, from 20 down to 10 BTU/SF…


10 ÷ 2 = 5


5 + 70 = 75 required fl oor surface temperature.


So at 35* outside (or 50%


But what if the customer wants the fl oor warmer? One of the most common com- plaints with a properly de- signed and installed radiant fl oor heating system is that the fl oor doesn’t always feel warm. The house may be perfectly comfortable, but the customer wants warm fl oors.


Page 1D


load), the floor only needs to be 75 degrees to heat the room up to an air temp of 70.


How about that!


They want warmer fl oors?


Turn the thermostat up! Look at what happens when we turn the thermostat up to 72* when it’s 35* degrees outside, and the BTU/SF heating load is 10:


10 ÷ 2 = 5


5 + 72 = 77 fl oor surface temperature.


By turning the t-stat up, we are, in fact, increasing the


BTUH/SF heating load. To continued on page 3D


Do you:


A: Boost the supply water temperature in the system? B: Install more tubing? C: Adjust the balancing valve to allow for more fl ow? D: Turn up the thermostat?


If you answered D, go to the head of the radiant class!


Turning up the thermostat isn't only the easiest is way to raise the fl oor surface tem- perature, it's also the most effective way.


And given the options, it's also the only way.


Radiant floor heating is a beautiful thing - it gives off BTU’s based solely on its surface temperature.


The


warmer the fl oor surface, the more BTU’s per square foot the radiant panel emits. That’s simple physics.


But what determines the required floor surface tem- perature?


Simple math, my friends… PST = (BTUH/SF load ÷ 2)


+ SPT


Where: • PST = Panel surface temperature required to


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