INSTALLATION, OPERATION AND MAINTENANCE MANUAL
Easco Boiler Corp 1175 Leggett Ave Bronx, NY 1047 T: 718.378.3000 F: 718.378.4560 [email protected] easco.com
Page 30 of 46
therefore, controlled by water temperature, but thermal expansion of the furnace is
restricted by water pressure. Because differential thermal expansions between the
furnace and the flue tubes or shell can result in excessive stresses in boiler components,
it is essential to consider the relationship between the boiler operating temperature
and boiler operating pressure. Consideration of this relationship leads to the conclusion
that a hot water Boiler should operate at a temperature not much below the saturation
temperature corresponding to the operating pressure.
5.9.1 Every effort should be made to keep the operating temperature of a hot water
Boiler as high as possible, thereby reducing temperature differentials between the
furnace tube and the flue tubes or shell. Easco has determined that for medium sized
Boilers this temperature difference should never exceed 100 °F. It is intuitive that for
larger Boilers the maximum temperature Difference should be even smaller.
5.9.2 For 30-psi hot water Boilers, the minimum permissible return water temperature
is 150 °F. For Boilers operating at higher pressures, the minimum permissible return
water temperature is a function of the operating pressure and the boiler size.
5.9.3 The return water temperature should always be within 40 °F to the supply
temperature.
5.9.4 Return water temperature should be continuously monitored. Anytime when
the return water temperature falls below any of the critical values, the burner firing rate
should be brought down to low fire. A low fire hold aquastat is provided for this purpose.
A low fire hold timer may be used in addition to the aquastat, but never in place of it.
5.9.5 A minimum water flow rate of 1/2 GPM/BHP is required to eliminate thermal
stratification. The burner circuit may be interlocked with a flow switch to assure that this
minimum flow rate is established prior to starting the burner.
5.9.6 The heating system must be designed to eliminate any possibility of a large
volume of cool water returning to a hot Boiler as may occur when pumps cycle or when
zone valves open.
5.9.7 Changes in boiler water temperature must occur gradually and should not exceed
2 °F per minute.
5.9.8 The burner-firing rate should be constant and as low as possible consistent with
the load demand in order to reduce the effects of component fatigue due to thermal
stress cycling. Any control system that causes a burner to cycle on and off at any rate
above low fire must be corrected.
5.9.9 The direction of water flow through the Boiler should always agree with the
instructions contained in the Care and Operations Manual provided with the Boiler.
5.9.10 In order to satisfy the Boiler’s operating requirements as listed above, the
judicious use of re- circulating pumps, slow-opening water valves and temperature
