Dunkirk WPSB Series 4
Model Number: 75-299 MBH
WPSB Series 4 is a natural-gas cast-iron steam boiler.
Technical Specifications
Source: manufacturer spec sheet · checked Sep 27, 2026
Prices depend on sizing, venting and piping in your home, so we quote every installation.
Sizing: the right size comes from a room-by-room heat-loss calculation, not the size of the old boiler or a rule of thumb. Oversized boilers short-cycle and waste fuel; steam systems are sized to the connected radiation instead. See how we approach boiler installation.
Home-Specific Operating Cost Review
No guaranteed annual savings or payback period
Historical Use
Fuel consumption and weather
Current Rates
Utility and delivered-fuel prices
System Design
Load, piping, controls, and temperatures
Full Specifications
- Model Number
- 75-299 MBH
- Efficiency (AFUE)
- 84.1%
- Boiler Type
- Steam Boiler
- Fuel
- natural gas
- Venting
- natural draft
- BTU Input Range
- 75k - 299k BTU
- Domestic Hot Water
- no
- In Production
- Yes
- Parts Warranty
- 5-yr parts
- Heat Exchanger Warranty
- 20-yr non-prorated
Specifications sourced from the manufacturer spec sheet, checked Sep 27, 2026.
Ideal For
Homes retaining steam radiators
Expert Review: Dunkirk WPSB Series 4
WPSB Series 4 is a natural-gas cast-iron steam boiler.
Dunkirk lists 75–299 MBH input, up to 84.1% AFUE, cast-iron push nipples, 20-year non-prorated limited exchanger coverage and five-year limited parts coverage. Venting on file: natural draft.
It is best suited to homes retaining steam radiators. Before replacing a steam boiler, a contractor should measure connected radiation (EDR), check the pickup allowance and plan near-boiler piping to the installation manual.
Pros: Built for steam, so it can replace a steam boiler without converting the radiators or piping. Multiple sizes (75–299 MBH input) allow sizing to connected radiator EDR. Considerations: Check specific steam rating against radiator EDR and review near-boiler piping.
Specifications on this page come from the manufacturer documents linked below; always confirm figures for the exact size being installed.
Key Features & Technology
Dunkirk lists 75–299 MBH input, up to 84.1% AFUE, cast-iron push nipples, 20-year non-prorated limited exchanger coverage and five-year limited parts coverage.
Venting on file: natural draft.
Advantages
- Built for steam, so it can replace a steam boiler without converting the radiators or piping.
- Multiple sizes (75–299 MBH input) allow sizing to connected radiator EDR.
Considerations
- Check specific steam rating against radiator EDR and review near-boiler piping.
Sizing & Installation Notes
Steam boilers like the WPSB Series 4 are sized to the connected radiation — we measure every radiator's EDR rating and match the boiler's steam output to that total, plus piping pickup allowance. Square footage rules of thumb don't apply to steam.
Every Dunkirk installation starts with a free in-home assessment covering the heat-loss calculation, venting and chimney condition, gas or oil supply sizing, and permit requirements for your town. Learn more about our boiler installation process and steam boiler installation, or see current rebate and incentive programs that may apply.
Warranty & Protection
Parts Warranty
5-yr parts
Heat Exchanger
20-yr non-prorated
Our Guarantee
100% Satisfaction
All Dunkirk boiler installations by Home+ Air & Heat include our 1-year workmanship warranty, covering labor and any installation-related issues.
Compare the Dunkirk Lineup
| Model | Efficiency | BTU Range | Fuel | Heat Exchanger Warranty |
|---|---|---|---|---|
| WPSB Series 4 (this model) | 84.1% AFUE | 75k - 299k BTU | natural gas | 20-yr non-prorated |
| Q95M | 95% AFUE | 80k - 200k BTU | natural gas/propane | 15-yr limited |
| DXL | 83.5% AFUE | Various sizes available | natural gas | — |
| XEB Series 4 | 84.4% AFUE | 43k - 188k BTU | natural gas | 20-yr non-prorated |
| Royal HE | 95.2% AFUE | 80k - 200k BTU | natural gas/propane | 10 years |
| DXL-K | 84% AFUE | 59k - 235k BTU | natural gas | 20-yr non-prorated |
| Royal CO (combi) | 95.2% AFUE | 80k - 200k BTU | natural gas/propane | 10 years |
| PSB | 82.7% AFUE | 75k - 299k BTU | natural gas | 12-yr limited |
See the full Dunkirk brand page for lineup context, or browse the Best Steam Boilers 2027 guide to compare across brands.
Frequently Asked Questions
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