Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
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title: Unit Heaters
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## Infiltration is the most commonly underestimated load. {note}
−## Loading-dock and overhead-door bays lose large quantities of heat whenever a door is open, and a heater sized only to the steady-state envelope loss will not recover the space. The heating-capacity selection shall account for the door-open infiltration load for the design door-open condition, not the closed-envelope load alone. {note}
+## Loading-dock and overhead-door bays lose large quantities of heat whenever a door is open, and a heater sized only to the steady-state envelope loss will not recover the space. The heating-capacity selection shall account for the door-open infiltration load for the design door-open condition, not the closed-envelope load alone.
### The heating-capacity selection shall include the infiltration and door-open heat loss for spaces served by overhead or large vehicular doors.
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## Freeze protection {note}
−## Hydronic and steam units installed in vestibules, loading docks, and other spaces that can fall below freezing when unoccupied are exposed to coil freeze damage, especially when served from a system without antifreeze. The design shall provide a freeze-protection strategy for any wet-coil unit in a freeze-exposed location. {note}
+## Hydronic and steam units installed in vestibules, loading docks, and other spaces that can fall below freezing when unoccupied are exposed to coil freeze damage, especially when served from a system without antifreeze. The design shall provide a freeze-protection strategy for any wet-coil unit in a freeze-exposed location.
### Hydronic unit heaters in freeze-exposed locations shall be provided with a freeze-protection means: a glycol-rated coil on a glycol system, a low-limit aquastat that maintains minimum coil temperature, or a coil drain provision, as scheduled.
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## The heating medium is the first selection and it cascades into nearly every other decision: capacity rating basis, control method, venting, clearances, and electrical or piping service. {note}
−## The four media in common use are hot water (hydronic), steam, gas-fired combustion (natural gas or propane), and electric resistance. Hydronic and electric units are the most common in new commercial construction; gas-fired units are common where a central heating plant is absent; steam units are now rare in new work but frequent in older industrial renovations and shall be supported where an existing steam distribution system is the available medium. {note}
+## The four media in common use are hot water (hydronic), steam, gas-fired combustion (natural gas or propane), and electric resistance. Hydronic and electric units are the most common in new commercial construction; gas-fired units are common where a central heating plant is absent; steam units are now rare in new work but frequent in older industrial renovations and shall be supported where an existing steam distribution system is the available medium.
### The unit-heater heating medium shall be selected from the available building distribution system or fuel source and coordinated with the Engineer of Record.
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## Heating capacity {note}
−## Heating capacity shall be established by a heat-loss calculation for the served space at the design conditions, including the infiltration provisions above. Capacity is expressed in MBH (thousands of Btu/h) for hydronic, steam, and gas units, and in kW for electric units. {note}
+## Heating capacity shall be established by a heat-loss calculation for the served space at the design conditions, including the infiltration provisions above. Capacity is expressed in MBH (thousands of Btu/h) for hydronic, steam, and gas units, and in kW for electric units.
### The scheduled heating capacity shall be derived from a heat-loss calculation for the served space and shall not be assigned by floor area alone.
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## Hydronic entering conditions {note}
−## For hot-water units the rated output depends on entering water temperature and flow; the design shall pin both so the certified rating matches the served load. {note}
+## For hot-water units the rated output depends on entering water temperature and flow; the design shall pin both so the certified rating matches the served load.
### The rated output of a hydronic unit heater shall be certified at the scheduled entering water temperature and design water flow.
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max: 93
step: 1
−setpoints: [60, 71, 82]
+setpoints: [49, 60, 71, 82, 93]
default: 82
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## Discharge orientation {note}
−## Horizontal-discharge units throw warm air across the space and suit lower mounting heights and wider coverage; vertical-discharge (downblow) units project heat to the floor from high mounting and suit tall spaces. Multi-position units can be field-set to either. The discharge orientation shall be coordinated with mounting height and the space geometry shown on the drawings. {note}
+## Horizontal-discharge units throw warm air across the space and suit lower mounting heights and wider coverage; vertical-discharge (downblow) units project heat to the floor from high mounting and suit tall spaces. Multi-position units can be field-set to either. The discharge orientation shall be coordinated with mounting height and the space geometry shown on the drawings.
### The discharge orientation shall be specified as horizontal, vertical (downward), or multi-position, coordinated with mounting height.
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## Controls integration is where the unit heater is most often left in a coordination gap, because the thermostat wiring falls between the mechanical and electrical drawings and the BAS scope. {note}
−## The control method ranges from a unit-mounted thermostat, through a remote wall thermostat, to full DDC control by the building automation system with a modulating valve on hydronic units or staged elements on electric units. The control method and the responsibility for control wiring shall be defined so the wiring does not fall into a scope gap. {note}
+## The control method ranges from a unit-mounted thermostat, through a remote wall thermostat, to full DDC control by the building automation system with a modulating valve on hydronic units or staged elements on electric units. The control method and the responsibility for control wiring shall be defined so the wiring does not fall into a scope gap.
### The control method shall be specified as unit-mounted thermostat, remote wall thermostat, or BAS/DDC control.
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- One spare fan motor per type
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