Viessmann Vitocrossal 300 CU3A-125 Floor-Standing Condensing Boiler, 125 MBH

Built for radiator retrofits and multi-zone fin-tube systems, the Viessmann Vitocrossal 300 CU3A-125 is a heat-only gas condensing boiler that stands on the floor. It modulates between 25 and 125 MBH, reaches 95% AFUE and holds about 13 gal of water for smooth, quiet operation.

A stainless-steel Inox-Crossal heat exchanger and self-calibrating MatriX dome burner produce a Net AHRI rating of 101 MBH, with efficiency up to 98% at low return temperatures. Sound runs from 33 dB at minimum to about 55 dB at maximum, and condensate reaches about 1.2 USG/h. The Vitotronic control provides outdoor reset, zone circuits and a start-up wizard; high-altitude use up to 10,000 ft requires electronic adjustment and de-rate.

Piping uses 1¼ in. NPTM heating supply and return, ¾ in. NPTF gas and PRV ports, a 3 in. (80 mm) flue with 3 in. combustion air, and a ¾ in. hose condensate outlet. Internals are factory pre-wired and piped, the unit is set for natural gas with LP conversion labels supplied, and it may be installed with zero distance to combustibles, allowing closet or alcove installs.

Highlights

• 25-125 MBH modulating input; Net AHRI 101 MBH

• 95% AFUE, up to 98% efficiency at low return temperatures

• High-mass design with about 13 gal water content

• Vitotronic outdoor-reset control with outdoor sensor

• Zero distance to combustibles allowed; 26 x 27 in. footprint

• ENERGY STAR; built to ASME Section IV and CSA B51

Specifications

In the box

• Vitotronic outdoor-reset control with outdoor sensor

• 30 psig PRV and fittings

• Temperature and pressure gauge

• LP conversion labels

Good to know

• Gas-fired appliance: it must be installed, vented and commissioned by a qualified installer in line with local codes and the manufacturer's installation manual.