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 ES23 and ES25 are chimney-vented cast-iron ES2 sizes at the same 85.0% AFUE. The ES25 doubles the input (140 vs 70 MBH) and roughly doubles capacity and water content while stepping the vent from 4 to 6 inches and adding about 99 lb — the same IQ Control System serves both.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | U.S. Boiler Company ES2 ES23 | U.S. Boiler Company ES2 ES25 |
|---|---|---|
| Input | 70 MBH | 140 MBH |
| DOE heating capacity | 59 MBH | 119 MBH |
| Net AHRI water rating | 51 MBH | 103 MBH |
| Efficiency (AFUE) | 85 % | 85 % |
| Vent size | 4" | 6" |
| Approx. shipping weight | 254 lb | 353 lb |
| Boiler water content | 2 gal | 4 gal |
| Dimensions (width × height × depth) | 12-3/4" × 41" × 33" | 18-1/2" × 41" × 33" |
| 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 non-condensing, chimney-vented cast-iron water boilers on the Intelligent Hydronic Control with the IQ Option Panel. The rating rows print 85.0% AFUE across the line, so efficiency is not the decision variable; the ES23 row is 70 MBH input with 59 MBH DOE heating capacity and 51 MBH net AHRI, while the ES25 is 140/119/103 MBH.
Physical differences follow the section count: the ES23 is 12-3/4 inches wide, 254 lb, with 2 gallons of boiler water and a 4-inch vent; the ES25 is 18-1/2 inches wide, 353 lb, with 4 gallons and a 6-inch vent. Both are 41 inches high and 33 inches deep with 1-1/4-inch supply and return connections.
The choice is driven by the calculated heat loss and radiation connected to the system. Oversizing a cast-iron boiler shortens run times and can reduce seasonal efficiency, so the smaller row should win when the load fits inside it.
U.S. Boiler Company
The U.S. Boiler Company ES2 ES23 is the smallest ES2 size with 2 gallons of boiler water: 70 MBH input with 59 MBH DOE heating capacity and a 51 MBH net AHRI water rating at 85.0% AFUE, chimney vented in 4" on the IQ Control System.
U.S. Boiler Company
The U.S. Boiler Company ES2 ES25 is the mid-size ES2 with a 6-inch vent: 140 MBH input with 119 MBH DOE heating capacity and a 103 MBH net AHRI water rating at 85.0% AFUE, chimney vented in 6" on the IQ Control System.
The ES25 lists a 6-inch vent against the ES23's 4-inch vent in the ES2 ratings table; vent diameter grows with boiler size across the line up to 8 inches on the ES29.
Yes — both use the Intelligent Hydronic Control with three-digit readout and the IQ Option Panel that accepts outdoor reset with DHW priority, low water cutoff and auxiliary high limit cards.
No. The ES2 is a cast-iron, chimney-vented boiler rated 85.0% AFUE; U.S. Boiler Company's condensing lines are the Alpine and K2 families.
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.