SlimFit
™
Series 3
gas
-
fired
water
boiler
—
Application Guide
Part number SF-E009-A/0516
2
- continued
• Stack / Vent Flow Rate for each individual boiler model is listed in the table below. This flow rate is
based on the unit running at 9.25% CO
2
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
SlimFit
boilers installed in a Cat-
egory 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.
I
mproper Installation of a Category II vent system resulting in positive pressure in the vent system can
result in flue gas spillage and carbon monoxide emissions, causing severe personal injury or death.
Weil-McLain recommends the use of a Variable Speed Chimney Fan/ Power venter to ensure that the
appropriate negative pressure is maintained for Category II venting. This is recommended because, as a
result of the boiler’s efficiency, the exhaust gas temperatures can be quite 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. The use of this device should be considered in any Engi-
neered Vent system.
Weil-McLain recommends the use of a Double Acting Barometric Damper or Modulating Damper to en-
sure the appropriate negative pressure range is kept for Category II venting. The use of this device should
be considered in any Engineered Vent system.
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
SlimFit
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.
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.
Increasing the negative pressure in the vent pipe will slightly increase the firing rate at low fire, thus reduc-
ing the boiler’s true modulation range. Consider this factor during system design.
Code Compliance
Venting / Combustion air piping – 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.
TABLE 1
Rating & Vent Data
Boiler
Model
Input
Btuh
Stack / Vent
flow rate
scfm
Negative Pressure to be
maintained at
Vent Connection of the boiler
Inches w.c.
SlimFit Vent
Adapter
required for
Category II
SF 550
550,000
128
-0.001 to -0.100
6”- 8”
SF 750
750,000
175
-0.001 to -0.100
6”- 8”
