3.8.2 System piping
System piping is connected to the boiler using 2½" NPT-Male threaded fittings. To simplify servicing, we
recommend using unions or flanged fittings, gate or ball valves at the boilers supply and return water
connections. You must install un-insulated hot water pipes with a minimum ¼" clearance from
combustible materials.
Fluid fill is most often accomplished by using a boiler regulator & fill valve set at 12 psig or more, with
the appropriate backflow prevention device as required by local code. This is acceptable in areas
where municipal water or well water has been treated and filtered to remove excessive minerals and
sediment, and water chemistry is known to be suitable for closed loop hydronic systems. In areas where
water quality is in question, or when chemical treatment or glycol is required, other options should be
considered. Follow the applicable codes and good piping practice.
Warning
Close the fill valve after any addition of water to the system, to reduce risk of water
escapement.
There are a number of boiler feed and pressurization devices on the market today that may be a better
choice than a raw water fill from the mains. When regular maintenance requires relief valve blow-off, the
discharge may be directed back into the pressurization unit for recycling of boiler fluid and chemicals
back into the system. In buildings that may be unoccupied for long periods of time, pressurization units
are useful to prevent flood damage should leakage occur from any component in the system. An
additional benefit is that backflow prevention devices are not required when using these devices.
Do not place any water connections above the boiler; leaks can damage the fan and controls. If
needed, create a shield over the top of the cover, but allow clearance for airflow and service access.
For best results, use a Primary/Secondary piping system, with a pumped boiler loop using 2½" piping.
Refer to Table 8 for boiler head loss information.
Example: In these EX models, the minimum flow rate required through the heat exchanger is 18
or 21 gpm (depending on model) and a maximum of 100 gpm is allowed. Primary/Secondary
piping ensures adequate flow and de-couples Δ°T issues (boiler vs. distribution). Aim for a 20°
to 30° F Δ°T across the heat exchanger at high fire (there is a boiler protection throttle fence
limiting the Δ°T to 80°F).
Check valves or thermal traps should be used to isolate both the supply and return piping for each load
- to avoid thermal siphoning and reverse flow.
To ensure adequate water flow through the boiler under high-head / single zone space heating
conditions, a pressure activated bypass or other means of bypass must be used on any load where the
flow rate might drop below minimum requirements (18 or 21 gpm - depending on model).
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