Kohler 20--2800 kW manual Double-Sleeve Thimbles

5.4 Double-Sleeve Thimbles

If the exhaust pipe should need to pass through a wall or roof, an exhaust thimble must be used to prevent exhaust pipe heat from being transmitted to the combustible material. Construction details for a typical double-sleeve thimble to be used where exhaust piping passes through a combustible roof or wall are shown in Figure 5-4. They are usually fabricated at a local sheet metal shop to the specifications furnished by the installation engineer.

The thimbles should be constructed so that they extend at least 10 inches (25.40 cm) both ways from the surface of the wall or roof. Holes are provided at both ends to allow cooling air to circulate through the thimble. If screening is used on the outer end to keep birds, rodents, etc., from entering the thimble, make sure that the mesh is large enough so that it doesn’t impair air circulation through the thimble. If the exhaust pipe must exit through a roof, a rain shield must be included above the thimble as shown in Figure 5-4. The rain cap as shown on the end of the exhaust pipe is recommended only in areas not subject to freezing temperatures. In an area where freezing is common, extend the exhaust

1

7

10

15

2

6

3

9

8 4

65

11

12

piping well beyond the roof and use a gradual “U” bend at the end to direct the exhaust outlet downward which will keep rain, snow, etc., out of the pipe. The outlet of the pipe should be far enough from the roof to prevent ignition of the roof material from hot exhaust.

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TP-5700-5

1.Rain cap (or gradual U bend)

2.Rain shield

3.10 in. (254 mm) minimum

4.1 in. (25 mm) minimum

5.Exhaust pipe

6.Ventilation holes at both ends

7.10 in. (254 mm) minimum

8.1 in. (25 mm) minimum

9.Flashing

10.Inner sleeve

11.Outer sleeve

12.Thimble outer diameter

13.10 in. (254 mm) minimum outside

14.10 in. (254 mm) minimum inside

15.Exhaust pipe diameter

Figure 5-4 Double-Sleeved Thimbles and Rain Cap

TP-5700 7/93 Section 5 Exhaust System 23