We report the characteristics of a 1 Watt hollow-core fiber gas laser, emitting continuous-wave in the mid-infrared. Our system is based on an acetylene-filled hollow-core optical fiber, guiding with low losses at both the pump and laser wavelengths and operating in the single-pass ASE regime. By systematic characterization of the pump absorption and output power dependence on gas pressure, fiber length and pump intensity, we determine that the reduction of pump absorption at high pump flux and the degradation of gain performance at high gas pressure necessitate the use of increased gain fiber length for efficient lasing at higher powers. Low fiber attenuation is therefore key to efficient high-power laser operation. We demonstrate 1.1 Watt output power at 3.1 μm wavelength by using a high-power EDFA pump in a single-pass configuration, approximately 400 times higher CW output power than in the ring cavity previously reported.