Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The RTS/28HE-6 and RTS/28HE-8 are adjacent sizes of Smith's high-efficiency 28HE RTS water boiler: 1,458 versus 1,985 MBH gross output, 1,268 versus 1,726 MBH net I=B=R water, and 143 versus 196 GPM at 20 °F ΔT. Both use 4" supply and return connections and the same Return Temperature Stabilizer; the -8 simply moves more water at a slightly higher printed thermal efficiency.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Smith RTS/28HE-6 | Smith RTS/28HE-8 |
|---|---|---|
| Gas burner capacity (as printed) | 1,773 MBH | 2,403 MBH |
| Gross output (as printed) | 1,458 MBH | 1,985 MBH |
| Net I=B=R water rating | 1,268 MBH | 1,726 MBH |
| Thermal efficiency — oil | 84.8 % | 85.2 % |
| Thermal efficiency — gas | 82.2 % | 82.6 % |
| Flow at 20 °F ΔT | 143 GPM | 196 GPM |
| Supply / return connection | 4" supply / 4" return | 4" supply / 4" return |
Both models are cast-iron wet-base water boilers from the current 28HE RTS line, documented in PDRTSHE-4. The model number counts sections: six for the -6 (43 HP, 129.4 sq ft heating surface) and eight for the -8 (59 HP, 177.6 sq ft). Burner capacity is 1,773 versus 2,403 MBH on gas, or 12.2 versus 16.6 GPH on light oil.
Printed thermal efficiency climbs slightly with size — 84.8% oil / 82.2% gas on the -6 against 85.2% / 82.6% on the -8 — and combustion efficiency is flat at 86.1% oil / 83.5% gas. The RTS (Return Temperature Stabilizer) is standard on both and is not a condensing device; RTSB-1 states the boiler cannot be operated as a condensing boiler, so low-temperature systems still need the return protection the RTS provides.
Both sizes use 4" supply and return connections. Flow at a 20 °F ΔT is 143 GPM for the -6 and 196 GPM for the -8, and water working weight rises from 5,861 to 7,507 lb. As with every 28HE RTS size, the load calculation decides: the -8 only earns its place when the plant genuinely needs the extra 500 MBH of gross output.
Smith Cast Iron Boilers
The Smith RTS/28HE-6 is the 6-section 43 HP size of the 28HE RTS high-efficiency water boiler — 1458 MBH gross output, 1268 MBH net I=B=R water, 1773 MBH gas or 12.2 GPH oil burner capacity, with 4" supply and return connections.
Smith Cast Iron Boilers
The Smith RTS/28HE-8 is the 8-section 59 HP size of the 28HE RTS high-efficiency water boiler — 1985 MBH gross output, 1726 MBH net I=B=R water, 2403 MBH gas or 16.6 GPH oil burner capacity, with 4" supply and return connections.
Slightly. PDRTSHE-4 prints 85.2% oil / 82.6% gas thermal efficiency for the -8 against 84.8% / 82.2% for the -6, with identical combustion efficiency (86.1% / 83.5%).
Yes. The PDRTSHE-4 water piping diagram prints 4" supply and 4" return connections for both the six- and eight-section sizes.
The Return Temperature Stabilizer distributes return water through the boiler to minimise thermal shock. RTSB-1 says it is standard on all Smith 28 and 28HE water boilers and that the boiler cannot be operated as a condensing boiler.
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.