Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The RS-8 and RS-11 are the two smaller Vitogas 050 commercial boilers and both print 85% combustion efficiency with two-stage firing at 70% partial load. The RS-11 adds three sections and three burners, lifting full-load input from 550 to 800 MBH and total weight from 1,280 to 1,709 lb, with a 12 in. vent collar against 10 inches.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Viessmann Vitogas 050 RS-8 | Viessmann Vitogas 050 RS-11 |
|---|---|---|
| CSA input, full load | 550 MBH | 800 MBH |
| CSA input, partial load | 372 MBH | 541 MBH |
| CSA output, full load | 468 MBH | 680 MBH |
| Combustion efficiency | 85 % | 85 % |
| Cast iron sections | 8 | 11 |
| Weight (with insulation, burners and packaging) | 1,280 lb | 1,709 lb |
| Boiler water content | 20 USG | 28 USG |
| Width | 921 mm | 1,255 mm |
| Vent pipe collar | 10 in | 12 in |
Both boilers are atmospheric cast-iron sectional units at 60 psig maximum operating pressure with 85% combustion efficiency. The RS-8 fires at 550 MBH (161 kW) full load / 372 MBH partial with 468 MBH (137 kW) full-load output; the RS-11 at 800 MBH (234 kW) / 541 MBH with 680 MBH (199 kW) output.
The RS-11 adds three cast-iron sections and three burners — 11 sections and 10 burners against eight and seven — growing width from 921 to 1,255 mm (36¼ to 49½ in) at the series' 883 mm depth and 1366 mm height. Weight rises from 1,280 to 1,709 lb (582 to 777 kg) and water content from 20 to 28 USG.
Connections stay 2 in. supply and return with ¾ in. boiler drains, while the gas connection grows from 1 to 1¼ in. and the vent pipe collar from 10 to 12 in. Both models use single- or two-stage burners; propane is not available in the two-stage configuration.
Viessmann
The Vitogas 050 RS-8 is the smallest commercial RS boiler: 550 MBH full-load input (161 kW), 468 MBH output and 85% combustion efficiency, two-stage fired with an 8-section block.
Viessmann
The Vitogas 050 RS-11 is the mid-size commercial RS boiler: 800 MBH full-load input (234 kW), 680 MBH output and 85% combustion efficiency with an 11-section block.
The RS-8 runs 550 MBH full load / 372 MBH partial and the RS-11 runs 800 MBH / 541 MBH, both two-stage at 85% combustion efficiency.
1,709 lb (777 kg) against 1,280 lb (582 kg) for the RS-8, with water content rising from 20 to 28 USG.
A 10 in. collar on the RS-8 and a 12 in. collar on the RS-11; the largest RS-14 uses 14 in.
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.