Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The step from the CU3A-125 to the CU3A-160 buys 35 MBH of input ceiling (160,000 against 125,000 BTU, 47 against 36.6 kW) but raises the minimum fire from 25,000 to 43,000 BTU (7.3 to 12.6 kW) and moves to the heavier chassis: 352 lb (160 kg) against 275 lb (125 kg), in a cabinet 4.5 inches deeper. Both are 95% AFUE floor-standing models, so the heat-loss calculation must justify the bigger unit.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Viessmann Vitocrossal 300 CU3A-125 | Viessmann Vitocrossal 300 CU3A-160 |
|---|---|---|
| Input, minimum | 25 MBH | 43 MBH |
| Input, maximum | 125 MBH | 160 MBH |
| Efficiency (AFUE) | 95 % | 95 % |
| Weight | 275 lb | 352 lb |
| Width | 26 in | 26 in |
| Depth | 27 in | 31.5 in |
| Height | 61.5 in | 61.5 in |
Both boilers sit on the same Vitocrossal 300 CU3A platform at 95% AFUE with the Inox-Crossal heat exchanger, MatriX dome gas burner, Lambda Pro control and 5:1 turndown. The 125 fires 25,000 to 125,000 BTU (7.3 to 36.6 kW); the 160 fires 43,000 to 160,000 BTU (12.6 to 47 kW).
The 160 moves to the larger chassis: 352 lb (160 kg) against 275 lb (125 kg), with depth growing from 27 inches (684 mm) to 31.5 inches (801 mm) while width (26 in / 660 mm) and height (61.5 in / 1562 mm closed) stay the same. The floor space and handling plan both change.
The 160's minimum fire is 18,000 BTU higher than the 125's, which matters in a low-load home where the boiler would spend long periods at minimum. Both models operate up to 194°F (90°C) and 10,000 ft (3,000 m), and neither is a combi; the choice follows the calculated load.
Viessmann
The Vitocrossal 300 CU3A-125 is the mid-size model of Viessmann Canada's floor-standing CU3A line: 25,000 to 125,000 BTU (7.3 to 36.6 kW) of input at 95% AFUE, weighing 275 lb (125 kg) in the compact floor-standing cabinet.
Viessmann
The Vitocrossal 300 CU3A-160 is the second-largest CU3A model: 43,000 to 160,000 BTU (12.6 to 47 kW) of input at 95% AFUE, weighing 352 lb (160 kg) in the deeper floor-standing cabinet.
352 lb (160 kg) against 275 lb (125 kg), per Viessmann Canada. The 160 is also 4.5 inches deeper (31.5 in / 801 mm against 27 in / 684 mm).
Yes. The 125 fires down to 25,000 BTU (7.3 kW) and the 160 only to 43,000 BTU (12.6 kW), so in a low-load home the 125 tracks mild weather more closely even though both are rated 95% AFUE.
When the heat-loss calculation plus hot-water recovery demand exceeds the 125's ceiling. Sizing beyond the calculated load just reduces the condensing time the boiler spends at low fire.
A consultation includes a heat-loss review so the size is right the first time.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
Facts checked September 8, 2026. Last updated September 8, 2026. Technical reviewer: not yet assigned.