Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
Both the Smith GBX-70 and the Smith GBX-105 belong to the Smith Cast Iron Boilers GBX Series (discontinued) line of non-condensing boilers. The Smith GBX-70 is rated 70 MBH input, 58 MBH gross output and 82.2% AFUE, and the Smith GBX-105 is rated 105 MBH input, 86 MBH gross output and 82.1% AFUE. Smith GBX-105 lists 35 MBH more input than Smith GBX-70 (105 MBH against 70 MBH). Smith GBX-70 carries the higher published AFUE at 82.2%, against 82.1%.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Smith GBX-70 | Smith GBX-105 |
|---|---|---|
| AGA input (as printed) | 70 MBH | 105 MBH |
| DOE heating capacity | 58 MBH | 86 MBH |
| Net I=B=R water rating | 50 MBH | 75 MBH |
| AFUE | 82.2 % | 82.1 % |
| Water content | 4.72 gal | 6 gal |
| Supply / return tappings | 1-1/2" NPT supply / 1-1/4" NPT return | 1-1/2" NPT supply / 1-1/4" NPT return |
| Fuel | Natural gas or propane | Natural gas or propane |
Published ratings: the Smith GBX-70 is rated 70 MBH input, 58 MBH gross output and 82.2% AFUE; the Smith GBX-105 is rated 105 MBH input, 86 MBH gross output and 82.1% AFUE. Smith GBX-105 lists 35 MBH more input than Smith GBX-70 (105 MBH against 70 MBH). Smith GBX-70 carries the higher published AFUE at 82.2%, against 82.1%.
The boiler water content differs: the Smith GBX-70 lists 4.72 gal, while the Smith GBX-105 lists 6 gal.
Both records print the same water connections (1-1/2" NPT supply / 1-1/4" NPT return) and fuel (Natural gas or propane), per the cited sources.
Smith Cast Iron Boilers
The Smith GBX-70 is a discontinued residential cast-iron water boiler rated 70 MBH AGA input with 58 MBH DOE heating capacity, 50 MBH net I=B=R and 82.2% AFUE, on 1-1/2" supply and 1-1/4" return tappings.
Smith Cast Iron Boilers
The Smith GBX-105 is a discontinued residential cast-iron water boiler rated 105 MBH AGA input with 86 MBH DOE heating capacity, 75 MBH net I=B=R and 82.1% AFUE, on 1-1/2" supply and 1-1/4" return tappings.
The Smith GBX-105 lists 105 MBH, against 70 MBH on the Smith GBX-70, per the cited documentation.
The Smith GBX-70 carries the higher published AFUE at 82.2%, against 82.1%.
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.