SECTION C: Installation
Termination
The vent terminal should be vertical and should termi- nate outside the building at least 2 ft above the highest point of the roof within 10 ft. The vent cap should have a minimum clearance of 4 ft horizontally from and in no case above or below (unless a 4 ft horizontal dis- tance is maintained) electric meters, gas meters, regulators and relief equipment. The distance of the vent terminal from adjacent public walkways, adjacent buildings, open windows and building openings must be consistent with the NFGC (U.S.) or B149.1 (Can- ada). Gas vents supported only by flashing and extending above the roof more than 5 ft should be se- curely braced to withstand snow and wind loads.
CAUTION: A listed vent cap terminal suitable for connection to the Cat IV vent materials, adequately sized, must be used to evacuate the flue products from the heaters.
Fig. 20: Vertical Venting
Common Venting
The NFGC does not address sizing guidelines for the common venting of multiple Category IV heaters. This is covered in the NFGC under “Engineered Vent Sys- tems”. Table L provides boiler discharge vent pressures at vent pressure switch and volumes of flue products at full fire for the calculation of appropriate vent sizing for common venting.
WARNING: Vent connectors serving any other appli- ances shall not be connected into any portion of mechanical draft systems operating under a positive pressure. If an MVB heater is installed to replace an existing heater, the vent system MUST be verified to be of the correct size and of Category IV
NOTE: For extractor sizing, typical CO2 levels are 8.5% for natural gas and 9.5% for LP gas and flue tem- perature of 300° F.
| Vent Size | Vent | Volume of | |
Model | Pressure | Flue Products | ||
(in.) | ||||
| (in. WC) | (CFM) | ||
|
| |||
503 |
| 0.1 | 160 | |
| 6 |
|
| |
753 | 0.2 | 240 | ||
1003 |
| 0.3 | 320 | |
|
|
|
| |
1253 |
| 0.2 | 400 | |
|
|
|
| |
1503 | 8 | 0.3 | 480 | |
|
|
| ||
1753 | 0.4 | 560 | ||
| ||||
2003 |
| 0.5 | 640 | |
|
|
|
|
* NOTE: Data for 100% firing rate.
Table L: Vent Pressure and Volume of
Flue Products Data
24
