Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
Boilers.ca is a brand of ROMA Heating & Cooling · Licensed gas contractor LGA0202903
Comparison
Verdict in brief
The K2WT-080B and K2WT-180B are the smallest and largest standard K2 watertube sizes, both 95.0% AFUE with 3-inch-capable venting to 135 equivalent feet. The 180B more than doubles input (18–180 vs 8–80 MBH) and capacity, gains 19 lb and moves to the wider 20-3/16-inch cabinet — and loses the 2-inch vent option.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | U.S. Boiler Company K2WT-080B | U.S. Boiler Company K2WT-180B |
|---|---|---|
| Input, minimum | 8 MBH | 18 MBH |
| Input, maximum | 80 MBH | 180 MBH |
| DOE heating capacity | 74 MBH | 169 MBH |
| Net AHRI water rating | 64 MBH | 147 MBH |
| Efficiency (AFUE) | 95 % | 95 % |
| Vent size | 2" or 3" | 3" |
| Approx. net weight | 100 lb | 119 lb |
| Dimensions (A × B × C) | 16-3/16" × 3" × 7-3/8" (A × B × C) | 20-3/16" × 4-7/16" × 8" (A × B × C) |
| Domestic hot water | Heating-only boiler — domestic hot water comes from a separate indirect tank or water heater | Heating-only boiler — domestic hot water comes from a separate indirect tank or water heater |
Both are direct-vent, sealed-combustion condensing boilers on the Sage2.3 control with a pre-installed boiler-loop circulator and the same 1-inch NPT water and 1/2-inch gas connections. Their rows both print 95.0% AFUE: the 080B at 8–80 MBH input with 74 MBH DOE heating capacity and 64 MBH net AHRI, the 180B at 18–180 MBH with 169/147 MBH.
The low-fire range matters in mild weather: the 080B modulates to 8 MBH while the 180B stops at 18 MBH. In a home whose load sits well under 100 MBH, the larger boiler reaches its minimum fire sooner and cycles more, which erodes the condensing advantage the K2 platform is bought for.
Venting and handling differ at the top: the 080B allows 2-inch or 3-inch venting (135 equivalent feet per side), the 180B is 3-inch only to the same length, and the cabinet grows from 16-3/16 to 20-3/16 inches wide while weight rises from 100 to 119 lb. Both remain wall hung with the supplied bracket.
U.S. Boiler Company
The U.S. Boiler Company K2WT-080B is the smallest K2 watertube size with the lowest 8 MBH minimum fire: 8–80 MBH input with 74 MBH DOE heating capacity and a 64 MBH net AHRI water rating at 95% AFUE on the K2 condensing platform.
U.S. Boiler Company
The U.S. Boiler Company K2WT-180B is the largest standard-altitude K2 watertube size: 18–180 MBH input with 169 MBH DOE heating capacity and a 147 MBH net AHRI water rating at 95% AFUE on the K2 condensing platform.
Only the K2WT-080B and K2WT-100B rows list the 2-inch option; from the K2WT-120B up, the data sheet lists 3-inch venting, in all cases to a typical maximum of 135 equivalent feet per side.
No — the K2WT-080B is listed at 100 lb and the K2WT-180B at 119 lb, and the 180B uses the wider 20-3/16-inch cabinet.
Only when the heat-loss calculation and hot-water recovery load exceed what the smaller K2 delivers. Below that, the 080B's lower minimum fire is the better match.
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.