Bosch AquaStar 250 SX - Applications and Sizing
BTU Input NG: 35,000 to 175,000
LP: 31,000 to 175,000
Energy Factor .85
Average Efficiency 87%
Ignition Electronic
Minimum Flow Rate (gpm) 0.8
Capacity 6.4 @ 45°F rise
5.3 @ 55°F rise
4.5 @ 65°F rise
3.9 @ 75°F rise
3.3 @ 90°F rise
Weight 47 lbs.
Dimensions 23 1/2" h by 15 3/4" w by 8 1/2" d
Modulationg Gas Valve Yes
Life Expectancy 20+ years

Model AquaStar Bosch 250SX - Installation Specifications
Voltage 120 VAC
Exhaust Vent Size 3-inch Stainless Steel Sealed Cat III
Combustion Air Pipe Size 3-inch PVC / Alum. / Galv.
Vent Options Horizontal or Vertical, Direct Vent Room Sealed Combustion
Exhaust Vent Termination Horizontal or Vertical
Gas Connection 3/4 inch Male NPT
Water Connections 3/4 inch Male NPT
Natural Gas Pressure Min: 5" WC
Max: 14" WC
Propane (LP) Gas Pressure Min: 11" WC
Max: 14" WC
Water Pressure Min: 30 PSI
Max: 150 PSI

What does Direct Vent or Room sealed mean? The 250SX can be installed in a small space with the ability to take in air from the outside via a 3 inch intake vent.
The Bosch AquaStar 250SX can be vented vertically or horizontally to the outside. The 250SX requires a dedicated 3" stainless steel single wall vent pipe. Other vent types will void the warranty and present a health hazard. The 250SX also requires an electrical connection for the electronic ignition.