Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
Both the Dunkirk PSB-3D and the Dunkirk PSB-4D belong to the Dunkirk Boilers PSB Plymouth Steam Boiler line of non-condensing boilers. The Dunkirk PSB-3D is rated 75 MBH input, 62 MBH heating capacity and 82.7% AFUE, and the Dunkirk PSB-4D is rated 112 MBH input, 91 MBH heating capacity and 82% AFUE. Dunkirk PSB-4D lists 37 MBH more input than Dunkirk PSB-3D (112 MBH against 75 MBH). Dunkirk PSB-3D carries the higher published AFUE at 82.7%, against 82%. Dunkirk PSB-4D lists 71 lb more shipping weight than Dunkirk PSB-3D (368 lb against 297 lb).
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Dunkirk PSB-3D | Dunkirk PSB-4D |
|---|---|---|
| Efficiency (AFUE) | 82.7 % | 82 % |
| Shipping weight | 297 lb | 368 lb |
| Dimensions (W x H x D) | 11-1/4" x 36-3/8 in. x 26-1/2 in. | 14-1/2" x 36-3/8 in. x 26-1/2 in. |
| Electrical | 120 V AC / 60 Hz / 1 phase, less than 12 A (15 A circuit recommended) | 120 V AC / 60 Hz / 1 phase, less than 12 A (15 A circuit recommended) |
| Fuel | Natural gas or propane | Natural gas or propane |
| Input (natural gas) | 75 MBH | 112 MBH |
| Input (propane) | 70 MBH | 105 MBH |
| Heating capacity (natural gas) | 62 MBH | 91 MBH |
| Heating capacity (propane) | 58 MBH | 85 MBH |
| Net AHRI steam rating (natural gas) | 47 MBH | 68 MBH |
| Net AHRI steam rating (propane) | 44 MBH | 64 MBH |
| Flue diameter | 5" | 6" |
| Connections | Return/supply 2-1/2 in. NPT; gas 1/2 in. NPT (75/112/150) or 3/4 in. NPT (187 MBH and larger) | Return/supply 2-1/2 in. NPT; gas 1/2 in. NPT (75/112/150) or 3/4 in. NPT (187 MBH and larger) |
| Control | Electronic low-water cut-off with 3/4 in. probe, pressure limit control, steam pressure gauge and glass water level gauge | Electronic low-water cut-off with 3/4 in. probe, pressure limit control, steam pressure gauge and glass water level gauge |
Published ratings: the Dunkirk PSB-3D is rated 75 MBH input, 62 MBH heating capacity and 82.7% AFUE; the Dunkirk PSB-4D is rated 112 MBH input, 91 MBH heating capacity and 82% AFUE. Dunkirk PSB-4D lists 37 MBH more input than Dunkirk PSB-3D (112 MBH against 75 MBH). Dunkirk PSB-3D carries the higher published AFUE at 82.7%, against 82%.
Dunkirk PSB-4D lists 71 lb more shipping weight than Dunkirk PSB-3D (368 lb against 297 lb). The dimensions differs: the Dunkirk PSB-3D lists 11-1/4" x 36-3/8 in. x 26-1/2 in., while the Dunkirk PSB-4D lists 14-1/2" x 36-3/8 in. x 26-1/2 in. The flue diameter differs: the Dunkirk PSB-3D lists 5", while the Dunkirk PSB-4D lists 6".
Both records print the same electrical requirement (120 V AC / 60 Hz / 1 phase, less than 12 A (15 A circuit recommended)), fuel (Natural gas or propane), connections (Return/supply 2-1/2 in. NPT; gas 1/2 in. NPT (75/112/150) or 3/4 in. NPT (187 MBH and larger)) and control (Electronic low-water cut-off with 3/4 in. probe, pressure limit control, steam pressure gauge and glass water level gauge), per the cited sources.
Dunkirk Boilers
The Dunkirk PSB-3D is a current cast-iron gas steam boiler: 75 MBH natural-gas input (70 MBH propane) for 62/58 MBH NG/LP heating capacity, a 47/44 MBH net AHRI steam rating (195/183 sq ft) at 82.7% AFUE, with a 5" flue and 297 lb shipping.
Dunkirk Boilers
The Dunkirk PSB-4D is a current cast-iron gas steam boiler: 112 MBH natural-gas input (105 MBH propane) for 91/85 MBH NG/LP heating capacity, a 68/64 MBH net AHRI steam rating (283/267 sq ft) at 82% AFUE, with a 6" flue and 368 lb shipping.
The Dunkirk PSB-4D lists 112 MBH, against 75 MBH on the Dunkirk PSB-3D, per the cited documentation.
The Dunkirk PSB-3D carries the higher published AFUE at 82.7%, against 82%.
It ships at 368 lb against 297 lb for the Dunkirk PSB-3D, per the cited sources.
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.