Installation Guide

Discussion on use of Schluter
®
-DITRA-HEAT for space heating
SPACE HEATING
ΔT* Total heat Output
°F (W/ft
2
) (Btu/hr/ft
2
)
2 0.9 3.2
4 2.0 6.8
6 3.1 10.6
8 4.3 14.6
10 5.5 18.6
12 6.7 22.8
14 7.9 27.0
16 9.2 31.3
18 10.4 35.6
20 11.7 40.0
ΔT* Total heat Output
°C (W/m
2
) (Btu/hr/m
2
)
1 8.9 30.4
2 19.1 65.2
3 29.9 101
4 41.0 140
5 52.4 179
6 64.0 218
7 75.9 259
8 87.9 300
9 100 341
10 112 383
34 SPACE HEATING
Schluter
®
-DITRA-HEAT is intended to warm tile floors and make them more comfortable underfoot but can also contribute to space heating. Floor warming is
a type of radiant heating that provides heat differently than from a forced air heating system, or from a baseboard heater or wall convector. As the tile covering
warms up, it will radiate heat to the surrounding objects in the room, which can increase the comfort level of the occupants.
What determines comfort?
Ambient temperature alone does not determine human comfort. This is already clear when one considers the outdoor environment. For example, meteorologists
will report the impacts of wind on perceived temperature in cold weather or humidity on perceived temperature in hot weather. We’ve all experienced the effect
of sun exposure in regard to perceived temperature as well. Sitting in the shade will feel cooler than sitting in the sun, despite the ambient temperature being
the same. This phenomenon applies to the interior environment as well.
How does radiant heating contribute to comfort?
In the interior environment, occupant comfort is primarily based on air temperature and the temperature of surrounding surfaces. Warmer surfaces, such as a
floor that incorporates heating elements, emit heat in the form of infrared radiation. This radiant heat does not directly warm the air, but warms the surrounding
objects and occupants, similar to the sun. Increases in air temperature result indirectly from convective heat from the warm objects. The temperature effect
on the occupant is referred to as the “mean radiant temperature”. “Operative temperature” is the average of air temperature and mean radiant temperature
and is what most directly determines the comfort of the occupant. Therefore, when radiant heating is present, occupants can feel the same level of comfort
at lower air temperatures.
Can I rely on DITRA-HEAT as the only heating source in my bathroom, kitchen, or living space?
In some cases the answer is yes. However, the amount of heat required to achieve a comfortable room depends on many variables that affect ambient
temperature and mean radiant temperature, including but not limited to the following.
• Starting temperature and target temperature
• Outdoor temperature and desired indoor temperature
• Heat loss through walls, windows, and doors according to size and R-value of the components
• Size of room and height of the ceiling
• Total heated surface area
All of these variables must be considered to calculate the required heat output of the system and determine if it can meet the needs of the owner. Schluter
Systems does not perform heating load calculations as a service and can’t make a final recommendation on the owner’s heating system requirements. It is
recommended that an HVAC professional be consulted to perform such an analysis and design. However, Schluter Systems offers the following information
to aid in the process and support the successful use of the DITRA-HEAT system.
The following notes are based on information gathered from articles and design guidebooks published by ASHRAE and other professional heating and cooling
associations. They are intended to help support successful use of the DITRA-HEAT system to enhance or provide space heating comfort. They do not
represent all variables or best practices that the heating professional must consider.
1. Operative temperature is what most directly determines the comfort of the occupant.
2. Since radiant heat contributes to approximately 55% of the total heat, the operative temperature is calculated as the average of air temperature
and mean radiant temperature.
3. Total heat output of the floor warming system to the space is proportional to the temperature differential between the floor surface and the
operative temperature.
4. The ideal operative temperature for occupants is typically between 68°F to 75°F (20°C to 24°C), depending on the level of activity.
5. The air temperature will typically be controlled at approximately 2°F to 3°F (1°C to 1.5°C) lower when the floor warming system is in use at
optimum conditions.
6. The recommended floor surface temperature is 84°F (29°C) or lower for comfort.
The heat output from the DITRA-HEAT system can be calculated using the recognized equation from various major heating and cooling engineering
associations. This equation takes into account the contribution from radiant heat and convective heat.
Q = 8.92ΔT
1.1
, where Q is in units of W/m
2
and ΔT is in units of °C
*ΔT = Temperature Differential between Floor Surface and Operative Temperature
For example, in a typical situation where the floor surface temperature is 82°F and the operative temperature is 72°F, the differential is 10°F, so the total heat
output from the floor surface is 5.5 W/ft
2
or 18.6 Btu/hr/ft
2
.