Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The CT3-37 and CT3-46 are the first two CT3 models on the wide 800 mm shell with a 10 in. vent pipe, and both print 97.2% combustion and thermal efficiency. The CT3-46 fires to 1726 MBH against 1389 MBH and holds 11.3 more USG of water, at 88 lb more shell weight.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Viessmann Vitocrossal 300 CT3-37 | Viessmann Vitocrossal 300 CT3-46 |
|---|---|---|
| Input | 1,389 MBH | 1,726 MBH |
| Output | 1,350 MBH | 1,675 MBH |
| Combustion efficiency | 97.2 % | 97.1 % |
| Thermal efficiency | 97.2 % | 97.1 % |
| Weight, boiler shell | 1,671 lb | 1,759 lb |
| Overall weight (with insulation and control, less burner) | 1,962 lb | 2,064 lb |
| Boiler water content | 129.5 USG | 140.8 USG |
| Maximum operating pressure | 30 psig | 30 psig |
Both boilers use the CT3 wide chassis — 800 mm shell width, 10 in. (251 mm) internal vent pipe, 30 psig maximum operating pressure and 210°F maximum supply temperature. The CT3-37 prints 1389 MBH (407 kW) input / 1350 MBH (396 kW) output; the CT3-46 prints 1726 MBH (506 kW) / 1675 MBH (491 kW).
The printed efficiency rows are identical at 97.2% combustion and 97.2% thermal efficiency. Water content rises from 129.5 to 140.8 USG (490 to 533 L) and shell weight from 1,671 to 1,759 lb (758 to 798 kg), with complete weights of 1,962 and 2,064 lb (890 and 936 kg).
As shipped the CT3-46 is 78 mm longer at 1,829 mm while width and height match at 800 mm and 2,023 mm. Both are documented in the CT3 technical data manual with output tables at three return-temperature conditions and standby-loss figures per size.
Viessmann
The Vitocrossal 300 CT3-37 opens the CT3 wide chassis: 1389 MBH input (407 kW), 1350 MBH output, 97.2% combustion and thermal efficiency and a 10 in. vent pipe.
Viessmann
The Vitocrossal 300 CT3-46 is the mid-size CT3 wide-chassis model: 1726 MBH input (506 kW), 1675 MBH output and 97.1% combustion and thermal efficiency.
Yes — both print 97.2% combustion efficiency and 97.2% thermal efficiency.
140.8 USG (533 L) against the CT3-37's 129.5 USG (490 L).
1389 MBH (407 kW) input / 1350 MBH output on the CT3-37, and 1726 MBH (506 kW) / 1675 MBH on the CT3-46.
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 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.