Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The 19HE-4 and 19HE-6 are two sizes of the same cast-iron 19HE power-burner boiler. The 19HE-4 prints 421 MBH gross output, 520 MBH gas / 3.6 GPH oil burner capacity and 2" supply and return piping, while the 19HE-6 prints 762 MBH gross, 938 MBH gas / 6.5 GPH oil and 3" piping. Both share the same 3" supply/return tappings, 15 psi steam / 80 psi water rating and the oil/gas/both firing choice; the decision is a heat-loss calculation, not the model number.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Smith 19HE-4 | Smith 19HE-6 |
|---|---|---|
| Gas burner capacity (as printed) | 520 MBH | 938 MBH |
| Gross output (as printed) | 421 MBH | 762 MBH |
| Net I=B=R water rating | 366 MBH | 663 MBH |
| Thermal efficiency — oil | 84.1 % | 83.7 % |
| Thermal efficiency — gas | 81.5 % | 81.2 % |
| Flue pipe diameter | 7" | 8" |
| Recommended supply / return piping | 2" supply / 2" return | 3" supply / 3" return |
Both models are wet-base cast-iron sectional boilers from the current 19HE line, documented in the same BSG-10 selection guide, G19HE-5 brochure and 19IOM-8R manual. The 19HE-4 has four sections and 12.5 boiler horsepower; the 19HE-6 has six sections and 22.8 horsepower. Neither is condensing — the 19HE is a chimney-vented power-burner design.
The published difference is capacity. BSG-10 prints 421 MBH gross output for the 19HE-4 against 762 MBH for the 19HE-6, with net I=B=R ratings of 366 versus 663 MBH water. Burner capacity scales with it: 520 versus 938 MBH gas, or 3.6 versus 6.5 GPH No. 2 oil. Thermal efficiency is essentially flat across the line (84.1% oil / 81.5% gas on the -4; 83.7% / 81.2% on the -6), so the larger size does not buy efficiency — it buys output.
Installation follows the size. 19IOM-8R Table 6 recommends 2" supply and return piping at 41 GPM for the -4 and 3" piping at 74 GPM for the -6, while the flue rises from 7" to 8". Sizing should follow the building's calculated heat loss plus pickup; choosing the -6 for a load that fits the -4 leaves the boiler cycling above the load and does not improve comfort.
Smith Cast Iron Boilers
The Smith 19HE-4 is a 12.5 HP cast-iron sectional power-burner boiler rated 421 MBH gross output — 520 MBH gas or 3.6 GPH No. 2 oil burner capacity — with a 7" flue connection and printed thermal efficiencies of 84.1% (oil) and 81.5% (gas).
Smith Cast Iron Boilers
The Smith 19HE-6 is a 22.8 HP cast-iron sectional power-burner boiler rated 762 MBH gross output — 938 MBH gas or 6.5 GPH No. 2 oil burner capacity — with a 8" flue connection and printed thermal efficiencies of 83.7% (oil) and 81.2% (gas).
The printed thermal efficiencies are within a fraction of a point: 84.1% oil / 81.5% gas for the 19HE-4 and 83.7% / 81.2% for the 19HE-6 (BSG-10). The real efficiency difference comes from matching the size to the load.
Yes. 19IOM-8R Table 6 recommends 2" supply and return for the 19HE-4 at 41 GPM and 3" for the 19HE-6 at 74 GPM, both at a 20 °F system drop.
Yes. The 19HE line is a power-burner boiler fired with oil, gas or both; BSG-10 prints both the gas burner capacity and the No. 2 oil firing rate for each size.
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.