WEIL-McLAIN 725 Commercial Condensing Gas-Fired Water Boilers User Manual
- June 9, 2024
- Weil-McLain
Table of Contents
WEIL-McLAIN 725 Commercial Condensing Gas-Fired Water Boilers
Common Venting methods and requirements for SVF Boilers (SVF 725/850)
The SVF boiler can be common vented when the following requirements are met.
- Common venting of the SVF boiler can only be done in a Category II vent system. All requirements for the SVF boiler to be vented in a Category II configuration must be met as stated in the SVF Boiler Manual or all subsequent addenda.
- SVF boilers can only be common vented with other SVF Boilers.
- The maximum number of SVF boilers to be common vented together is four.
- The Vent system for a Category II SVF boiler is considered a Designed / Engineered vent system and should be designed by a professional using accepted engineering practices.
- Vertical Vent only.
- Combustion air must come from the boiler room. See Direct Exhaust – Room Air Openings requirements in the SVF Boiler Manual.
- Must increase venting to 8” using a 6” to 8” bell reducer at boiler vent adapter for Category II Vent Connection.
Hazard Definitions
The following defined terms are used throughout these Instructions to bring attention to the presence of hazards of various risk levels or to important information concerning the life of the product.
WARNING: Warning indicates the presence of hazards that can result in severe personal injury, death, or substantial property damage.
IMPORTANT: Important indicates additional information that is important, but is not related to personal injury or property damage.
- The Vent System should be designed so that the pressure in the vertical 8” vent pipe immediately following the bell reducer is between the ranges provided in Table 1, during all operating conditions (i.e., High Fire through Low Fire, prepurge, post purge and ignition). If a negative pressure cannot be guaranteed at prepurge and post purge, a backflow preventer is required on each boiler’s vent.
WARNING: To prevent backflow through boiler, negative pressure must be maintained in vent system at all times including prepurge and post purge cycles. Failure to comply can result in severe personal injury, death, or substantial property damage.
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Flue gas temperature should not exceed 210°F; the boiler will shut down and recycle if it does. The flue gas temperature should typically be within 20°F of the return water temperature of the boiler. If there is the potential for a wide variation in return water temperatures, the lowest possible temperature should be used for any calculations.
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Stack / Vent Flow Rate for each individual boiler model is listed in Table 1. This flow rate is based on the unit running at 9.25% CO2 (natural gas), and the maximum flue gas temperature of 210°F.
The values can vary depending on the location of the installation and operating conditions. -
A carbon monoxide detector(s) is required in the boiler room for SVF boilers installed in a Category II configuration. The carbon monoxide detector must be wired on the same electrical circuit as the boiler. Check your local codes for any additional requirements of carbon monoxide detectors.
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WARNING: Improper Installation of a Category II vent system resulting in positive pressure in the vent system can cause flue gas spillage and carbon monoxide emissions, which can result in severe personal injury or death.
IMPORTANT
- Weil-McLain recommends the use of a Variable Speed Chimney Fan or Power Venter to ensure that the appropriate negative pressure is maintained for Category II venting. As a result of the boiler’s efficiency, the exhaust gas temperatures can be low resulting in less natural draft. A flow proving switch should be wired into the Proof of Closure jumper circuit on the boiler control. See the boiler manual for additional information.
- Weil-McLain recommends the use of a Double Acting Barometric Damper or Modulating Damper to ensure the appropriate negative pressure range is kept for Category II venting.
- When using a damper of any kind, it is recommended to use a thermal spill switch to detect any exhaust flow into the boiler room. Verify the temperature range on the thermal spill switch is adequate for the Flue gas temperature from the SVF boiler. The use and set-point of this shall be determined by the system designer. The Auto reset input on the Boiler’s control can be used to wire in the thermal spill switch.
Boiler Model
|
Input Btuh
| Stack / Vent flow rate (scfm)| Negative pressure to be maintained at the vent connection of the boiler
(inches w.c.)
|
SVF vent adapter required for Category II
---|---|---|---|---
SVF 725| 725,000| 149| -0.001 to -0.100| 8″
SVF 850| 850,000| 175| -0.001 to -0.100| 8″
IMPORTANT: The thermal spill switch should shut down all boilers connected to the common flue. Each boiler must be wired to its own set of dry contacts activated by the spill switch.
IMPORTANT: Increasing the negative pressure in the vent pipe will slightly increase the firing rate at low fire, thus reducing the boiler’s true modulation range. Consider this factor during system design.
Code Compliance
WARNING
Provisions for combustion and ventilation air must be made in accordance with the codes listed below. Failure to comply can result in severe injury, death, or substantial property damage. Installations must provide provisions for combustion and ventilation air in accordance with the section “Venting of Equipment”, of the National Fuel Gas Code, ANSI Z223.1 / NFPA 54, or “Venting Systems and Air Supply for appliances” of the Natural Gas and Propane Installation Code, CAN/CSA B149.1, or applicable provisions of the local building codes. The figure below represents a general common venting approach. The Vent system for a Category II SVF boiler is considered a designed engineered vent system and should be designed by a professional using accepted engineering practices.
WM Technologies, LLC 500 Blaine Street Michigan City, IN 46360-2388
Telephone: 800-654-2109 weil-
mclain.com