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U.S. Boiler Company · Series
The K2 is U.S. Boiler Company's value-positioned condensing gas boiler family — the K2 Firetube (six wall-hung sizes, combi available at 155 MBH), the K2 Combi and the K2 Watertube, whose printed rating rows K2WT-080B through K2WT-180M run 8–80 up to 18–180 MBH input at 95.0% AFUE (94.5% on the high-altitude 180M) on the Sage2.3 control.
Series facts
The K2 ratings table prints 95.0% AFUE on K2WT-080B through K2WT-180B and 94.5% on K2WT-180M, the high-altitude model; the page headline is 95% AFUE with 10:1 turndown.
The K2 family is U.S. Boiler Company's condensing gas boiler line, published on the official site in three product pages: K2 Firetube, K2 Combi and K2 Watertube. The Firetube page describes the newer stainless-steel vertical firetube heat exchanger line — 'six wall hung models; 85, 110, 155, 205, 270 MBH (combi version available for 155 MBH)' — with 5:1 modulation, the Sage2.2 control and a 95% efficiency headline. The K2 Combi page describes a 95% AFUE combi with 10:1 turndown, a flat-plate heat exchanger, the factory pre-set Sage2.3 control system, a touch-screen diagnostic display and a free five-year parts warranty. The K2 Watertube page remains live with the K2 Product Data Sheet, and the Firetube page describes the Firetube as joining the K2 Watertube boiler.
The K2 Product Data Sheet (Form USBL14061) prints the watertube ratings table documented at model level here: K2WT-080B (8–80 MBH input, 74 MBH DOE heating capacity, 64 MBH net AHRI, 2" or 3" vent, 100 lb), K2WT-100B (10–100 MBH, 94/82 MBH, 2" or 3", 102 lb), K2WT-120B (12–120 MBH, 112/97 MBH, 3", 105 lb), K2WT-150B (15–150 MBH, 142/123 MBH, 3", 119 lb), K2WT-180B (18–180 MBH, 169/147 MBH, 3", 119 lb) and K2WT-180M (18–180 MBH, 168/146 MBH, 3", 119 lb, 94.5% AFUE). All rows print 95.0% AFUE except the 180M, which the data sheet states is for installations above 2,000 feet.
The data sheet lists a pre-installed boiler-loop circulator, separated high/low-voltage junction box, the Sage2.3 control with touch screen, self-guided menus and built-in diagnostics, two additional circulator outputs, an eight-boiler sequencer, outdoor reset with sensor, DHW priority, warm-weather shutdown, a universal exhaust vent connection for CPVC/PVC, polypropylene and stainless steel, a flow switch, supply/return/high-limit water sensors, a pre-installed hanging bracket and wall-mount kit, and optional FastPipe primary/secondary adapters, floor stand, LWCO and Sage Zone Control panels. No printed rating table is published for the K2 Firetube or K2 Combi on the official site, so those siblings are documented at series level only; no official Canadian-sales statement was found, so canadianStatus stays 'unknown'.
Highlights
Free five-year parts warranty included per the K2 Product Data Sheet; the product page repeats the five-year parts warranty.
Models
One canonical page per model with input, output and efficiency kept separate.
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-100B is the second size, keeping the 2-inch vent option: 10–100 MBH input with 94 MBH DOE heating capacity and a 82 MBH net AHRI water rating at 95% AFUE on the K2 condensing platform.
U.S. Boiler Company
The U.S. Boiler Company K2WT-120B is the last size in the compact 16-3/16-inch-wide cabinet: 12–120 MBH input with 112 MBH DOE heating capacity and a 97 MBH net AHRI water rating at 95% AFUE on the K2 condensing platform.
U.S. Boiler Company
The U.S. Boiler Company K2WT-150B is the first of the wider 20-3/16-inch cabinet sizes: 15–150 MBH input with 142 MBH DOE heating capacity and a 123 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.
U.S. Boiler Company
The U.S. Boiler Company K2WT-180M is the high-altitude variant of the 180, stated for installations above 2,000 feet: 18–180 MBH input with 168 MBH DOE heating capacity and a 146 MBH net AHRI water rating at 94.5% AFUE on the K2 condensing platform.
| Specification | U.S. Boiler Company K2WT-080B | U.S. Boiler Company K2WT-100B | U.S. Boiler Company K2WT-120B | U.S. Boiler Company K2WT-150B | U.S. Boiler Company K2WT-180B | U.S. Boiler Company K2WT-180M |
|---|---|---|---|---|---|---|
| Input, minimum | 8 MBH | 10 MBH | 12 MBH | 15 MBH | 18 MBH | 18 MBH |
| Input, maximum | 80 MBH | 100 MBH | 120 MBH | 150 MBH | 180 MBH | 180 MBH |
| output-max | — | — | — | — | — | — |
| Efficiency (AFUE) | 95 % | 95 % | 95 % | 95 % | 95 % | 94.5 % |
| turndown | — | — | — | — | — | — |
| vent-max-3 | — | — | — | — | — | — |
| vent-max-2 | — | — | — | — | — | — |
| Approx. net weight | 100 lb | 102 lb | 105 lb | 119 lb | 119 lb | 119 lb |
Read the full comparison: U.S. Boiler Company K2WT-080B vs K2WT-180B →
Read the full comparison: U.S. Boiler Company K2WT-080B vs K2WT-100B →
Read the full comparison: U.S. Boiler Company K2WT-100B vs K2WT-120B →
Read the full comparison: U.S. Boiler Company K2WT-120B vs K2WT-150B →
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Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Services for U.S. Boiler Company boilers
The six K2 watertube rating rows printed in the K2 Product Data Sheet: K2WT-080B, K2WT-100B, K2WT-120B, K2WT-150B, K2WT-180B and K2WT-180M. The K2 Firetube and K2 Combi pages publish marketing copy but no rating table, so they are covered by this series page.
Both print 18–180 MBH input, 3" venting and 119 lb, but the 180M row prints 168 MBH heating capacity, 146 MBH net AHRI and 94.5% AFUE and is stated for installations above 2,000 feet, while the 180B prints 169/147 MBH and 95.0% AFUE.
No. The Firetube uses a stainless-steel vertical firetube heat exchanger and the product page lists six sizes with a 155 MBH combi version; the Watertube is the sibling line whose printed rating rows appear in the K2 Product Data Sheet. Both are described on the official site as part of the current K2 series.
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Sources and verification
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.