![](/images/new-backgrounds/1308066/30806613x1.webp)
INSTALLATION” under the
A
DIRECT VENTING INSTRUCTIONS (two pipe system)
DETERMINING VENT LENGTH
See Table 1 for maximum vent and
Table 1 shows the maximum allowable pipe lengths for direct vent systems depending on:
??altitude (elevation) of the installation
??gas input rating of furnace
??diameter of the air and vent pipes
??number of elbows
Note that some of the larger furnace models may require a high altitude pressure switch at elevations between 3000 and 6000 feet. For example, the table shows that the 126,000 Btu/hr model may need a high altitude pressure switch when installed at elevations between 3000 and 4000 feet. Above 4000 feet, this model requires a high altitude switch for all installations.
All furnace models require the high altitude pressure switch when installed at elevations above 6000 feet.
The
NOTE: Table 1 assumes Sweep 90? elbows like that in
Figure 3a. If using Hard 90? elbows similar to the one in Figure 3b, decrease the vent length by 3 feet for every elbow used.
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| (b) |
Figure 3. (a) Sweep 90? Elbow. (b) Hard 90? Elbow.
When using a concentric vent kit the following exceptions apply:
??90,000 BTU input furnaces must be vented with 3 -inch pipe.
??For 108,000 BTU input furnaces, reduce the maximum vent length by 5 feet when 2 sweep elbows are used, 10 feet when 3 sweep elbows are used, 15 feet when 4 sweep elbows are used and so on. For hard 90° elbows reduce vent length in 8 -foot intervals.
??126,000 BTU input furnaces may not be vented using a concentric vent.
Installer’s Information Manual | Page 7 |