Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The IN3I and IN4I are the two smallest chimney-vented Independence steam boilers, both 82.0% AFUE. The IN4I raises input from 62 to 105 MBH, net steam from 38 to 65 MBH (158 to 271 sq ft) and chimney requirement from 4×15 to 5×15 inches, adding 70 lb.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | U.S. Boiler Company Independence IN3I | U.S. Boiler Company Independence IN4I |
|---|---|---|
| Input | 62 MBH | 105 MBH |
| DOE heating capacity | 51 MBH | 87 MBH |
| AHRI net steam rating | 38 MBH | 65 MBH |
| Steam square feet | 158 sq ft | 271 sq ft |
| Efficiency (AFUE) | 82 % | 82 % |
| Minimum chimney requirements | 4×15 in chimney | 5×15 in chimney |
| Approx. shipping weight | 350 lb | 420 lb |
| Domestic hot water | Heating-only boiler — domestic hot water comes from a separate indirect tank or water heater | Heating-only boiler — domestic hot water comes from a separate indirect tank or water heater |
Both are cast-iron, gas-fired steam boilers at 15 PSI maximum working pressure with electronic ignition, stainless-steel burners, a step-opening gas valve, probe-type LWCO and a 15 PSI safety valve. Their rating rows both print 82.0% AFUE, so the decision is the connected steam load: 38 MBH net steam (158 sq ft) on the IN3I against 65 MBH (271 sq ft) on the IN4I.
Chimney requirements step with the section count: the IN3I lists a 4×15-inch round chimney and the IN4I a 5×15-inch, both measured 15 feet from top of drafthood to top of chimney. Shipping weight rises from 350 to 420 lb.
For homes without a chimney, the same two capacities appear in the power-vented line as the IN3PVNI (62 MBH input, 83.2% AFUE) and IN4PVNI (105 MBH input, 82.2% AFUE), which vent through 3-inch AL29-4C stainless steel at 35–45 equivalent feet instead of a chimney.
U.S. Boiler Company
The U.S. Boiler Company Independence IN3I is the smallest chimney-vented Independence: 62 MBH input with 51 MBH DOE heating capacity and a 38 MBH AHRI net steam rating at 82% AFUE, chimney vented (4×15 in chimney).
U.S. Boiler Company
The U.S. Boiler Company Independence IN4I is the second chimney-vented size: 105 MBH input with 87 MBH DOE heating capacity and a 65 MBH AHRI net steam rating at 82% AFUE, chimney vented (5×15 in chimney).
The IN3I and IN4I are the two smallest of the seven chimney-vented Independence sizes; the line continues to the IN9I at 280 MBH input.
Yes — the ratings table notes LP conversion kits are available on the chimney-vented IN3I–IN9I models.
The IN3I lists a 4×15-inch round chimney and the IN4I a 5×15-inch, both 15 feet minimum height from top of drafthood to top of chimney per the data sheet.
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.