HIGHLANDER WOOD–FIRED BOILER – INSTRUCTION MANUAL
HIGHLANDER 13 Nov-09
connection of the special safety by-pass zone valve and blow down system as described
above. For plumbing details see Fig. TW-4.
2.6.2 PARALLEL PIPING SYSTEM
In the PARALLEL SYSTEM the water is circulating between the two boilers by means of an
auxiliary circulator. In this system the flow of water from the existing boiler (supply) is teed and
piped to the return of the Kerr Highlander boiler. The return pipe to the existing boiler is teed,
and piped to the outlet nipple of the Kerr Highlander boiler. Therefore the Highlander is
maintaining heat in both boilers. If the Highlander is not being utilized the system warm return
water is not keeping the wood boiler warm.
In the parallel system an auxiliary circulating pump keeps the temperature even between the
two boilers. It is controlled by a separate aquastat on the Kerr Highlander boiler. When the
water in the Kerr Highlander boiler is hotter than the set point of the single aquastat, the
circulator comes on and circulates the hot water between the two units.
This system allows the domestic hot water coil in the existing boiler to supply the household
with hot water without an additional coil in the Kerr Highlander boiler.
2.6.3 BOILER RETURN WATER TEMPERATURE
Steel boilers are very susceptible to corrosion caused by condensation of flue gases. In order
to prevent this, the return water temperature must not fall below 140°F. Most hydronic
systems are designed for a delta T of 20°F. Therefore, the low limit should be set at no lower
than 170°F, which accounts for the -10°F differential of the triple aquastat. Heating systems
that require lower temperatures such as cast iron radiators and radiant systems require some
form of mixing device to ensure the return water is at or above 140°F. The warranty will not
be valid for steel boilers with return temperatures below 140°F. For more information
refer to B214-01 Installation Code for Hydronic Heating Systems (or equivalent).
2.7 CONTROL SYSTEM
The Kerr Highlander boiler control system serves the following functions:
1) Maintaining the boiler water temperature by controlling the combustion air entering the
boiler. A double pole, double throw aquastat and the air damper control this function.
2) Protects the Kerr Highlander boiler from an overfire by overriding the home’s thermostat
and by putting any excess heat into the living area. Opening the “normally open by-pass
zone valve” and turning on the circulator accomplish this.
3) To allow the Kerr Highlander boiler to operate as a gravity heating system in the event of
a power failure, the “normally open by-pass zone valve” will automatically spring open in a
power off situation.
4) Kerr Highlander boiler “BLOW-DOWN” fire extinguishing system. In the case of extreme
over firing the pressure in the boiler will exceed 30 PSI. When this happens, a relief valve
will open and allow steam to escape into the firebox area, damping the fire. See Fig. TW-
8 showing the fitting for the installation of the fire extinguishing system.
IMPORTANT: Upon completion of the installation, a change over from one fuel to the other
shall not require manual adjustment of any controls other than the thermostat.
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