Model VIP+
19
Owner's Manual
Thermal Expansion
General Considerations
1.
When Model VIP+ is in use, thermal expansion will occur on the inner flue and outer casing.
2.
A good estimation for thermal expansion is approximately 1" per 100' chimney length per 100°F of temperature rise between the flue
gases and the surroundings temperatures.
Thermal Expansion (inch) = ( Length (feet) / 100 ) x (
∆
T (°F) / 100 )
3.
Whether in the vertical or the horizontal run, the thermal expansion of the inner pipe depends on the inner flue temperature and the length
of the chimney between two fixed points.
4.
Good installation requires that expansion greater that 1/4” must be compensated with either a Bellow Joint or an Expansion Length. The
selection of the expansion joint device depends on the system pressure* :
*For engine or turbine exhaust system requiring pressures up to 60 inches of water column, or where the construction must be absolutely
gas tight, all Bellows Joints are recommended for expansion and vibration movements of the exhaust.
*Low pressure systems, such as boilers (up to 6 inches water column), can effectively use the Expansion Length.
Table 9 - Allowable lengths for 1/4” thermal expansion
∆T (Gas T – Surroundings T) (°F)
Length between fixed points
200
12'6"
300
8'4"
400
6'3"
500
5'0"
600
4'2"
700
3'7"
800
3'1"
900
2'9"
1000
2'6"
5.
Tees and Elbows are not designed to resist bending moment forces as a result of thermal expansion. The forces due to thermal expansion
therefore need to be compensated by expansion joints.
6.
Expansion joints are not designed to withstand lateral forces so they must be properly supported and guided.
7.
Because the amount of outer casing movement is the same as the inner flue, the outer casing must slide to avoid excessive forces on
tees, elbows or fixed points. To accommodate outer casing movements, wall guide, floor guide and suspension bands must allow
movement of the chimney.
8.
When re-supporting a system with considerable height and thermal expansion, Expansion Lengths or Bellow Joints must be used just
below every fixed support above the first to compensate for thermal expansion.
9.
Spacing of Guides and Supports, when a thermal expansion part is used, should not be greater than that specified in
table-6 and -7
.
10.
Proper guiding and support of expansion parts often requires closer spacing.
