Stiebel Eltron 234050, 234047 Sizing Guide
TECHNICAL SERVICE BULLETIN
How to size SunWarmth™ CIR heaters to heat a space
Simply the Best
The size and quantity of heaters (the amount of heat
input) required for comfort in an area is affected by
several factors.
› The chilling effect of air movement in an area (outside
or inside) requires additional heat input, so provide
wind breaks wherever possible.
› Any area heated outdoors is “spot heat.”
› “Spot heating” comfort is most effective if people are
heated from at least two sides.
› When "spot heating” only part of a cold indoor area,
factor the activity level of the people: seated at rest,
hard physical labor, etc.
› Space heaters uniformly around the perimeter (and if
required, in the center or throughout the area) to provide sufficient heat density to accomplish the desired
temperature rise.
› Heating the space in an entire structure requires an
accurate heat loss calculation and is beyond the scope
of this TSB. Contact Stiebel Eltron for assistance.
To calculate the number of heaters required for an area,
determine the size of the area and the amount of heat
input required to achieve a comfortable temperature in
the space. Here is a checklist for the calculations.
› In what seasons is comfort required and what is the
outside design temperature?
› What temperature rise is desired for comfort? (10°,
15°, 20°, 25°?)
› Calculate the required input to get the desired aver-
age temperature rise using Table 1 to determine Heat
Density Per Degree.
› Use this formula to calculate the amount of heater
wattage required for the space:
Input = Site Length × Site Width × Temperature Rise
× Heat Density per Degree
› Example:
Outdoor patio: 30 feet long by 10 feet wide
Desired temperature rise: 20°F (area average)
30 × 10 × 20 × 2 = 12,000 Watts total input required
› Use the total wattage required to determine the
number of heaters needed, making sure placement
follows the guidelines for safety and comfort.
Mounting and Coverage Information
H
Model Wattage
CIR 150-1 I, CIR 150-1 O 1500 W Minimum: 7´ (2.1 m)
CIR 200-2 O 2000 W Minimum: 8´ (2.4 m)
CIR 400-2 O 4000 W Minimum: 10´ (3.0 m)
17 West St., W. Hatfield, MA 01088 | 800.582.8423 | 413.247.3380 | fax 413.247.3369 | info
Mounting
height
Maximum: 8´ (2.4 m)
Maximum: 9´ (2.7 m)
Maximum: 11´ 6˝ (3.5 m)
A
Length
heated
8´ 10˝ (2.7 m)
9´ 10˝ (3.0 m)
9´ 10˝ (3.0 m)
11´ 2˝ (3.4 m)
11´ 10˝ (3.6 m)
13´ 5˝ (4.1 m)
Table 1
Input Required per Area per Degree Comfort Temperature Rise
Outdoor heating
(up to 10 mph wind)
Indoor spot heating
(protected area, low
air movement)
Dimensions of area heated
B
Width heated
close to heater
8´ 6˝ (2.6 m)
9´ 2˝ (2.8 m)
9´ 2˝ (2.8 m)
9´ 10˝ (3.0 m)
11´ 2˝ (3.4 m)
14´ 1˝ (4.3 m)
C
Width heated
far from heater
16´ 1˝ (4.9 m)
18´ 1˝ (5.5 m)
18´ 1˝ (5.5 m)
20´ (6.1 m)
23´ (7.0 m)
27´ 7˝ (8.4 m)
Heat density per °F
W/(ft2)/°F
2 40
0.75
D
Size of
heated area
2
(10.1 m2)
108 ft
133 ft2 (12.4 m2)
2
(12.4 m2)
133 ft
165 ft2 (15.3 m2)
205 ft2 (19.0 m2)
275 ft2 (25.4 m2)
@
stiebel-eltron-usa.com | www.stiebel-eltron-usa.com
Heat density per °C
W/(m2)/°C
14
E
Average
heat density
13.9 W / ft2 (148.5 W / m2)
11.3 W / ft2 (121.0 W / m2)
15.0 W / ft2 (161.3 W / m2)
12.1 W / ft2 (130.7 W / m2)
19.5 W / ft2 (210.5 W / m2)
14.5 W / ft2 (157.5 W / m2)
rev. 2-2015
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