Canada-wide gas boiler information · On-site service in Greater Vancouver, BC
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Comparison
Verdict in brief
The Ultra 230 is the efficiency peak of the Series 4 line at 94.1% AFUE — the figure behind the CA page's up-to-94.1% claim — stepping input from 155 to 230 MBH and low fire from 31 to 46 MBH, with 3" venting limited to 30 ft unless the route runs 4".
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Weil-McLain Ultra 155 | Weil-McLain Ultra 230 |
|---|---|---|
| Input, maximum | 155 MBH | 230 MBH |
| Input, minimum | 31 MBH | 46 MBH |
| DOE heating capacity | 139 MBH | 207 MBH |
| Net AHRI water rating | 121 MBH | 180 MBH |
| Efficiency (AFUE) | 94 % | 94.1 % |
| Weight | 234 lb | 246 lb |
| Boiler water content | 1.17 gal | 1.57 gal |
| Venting | 3" PVC, CPVC, polypropylene or stainless steel (Category IV); 3" pipe only on the 155 | 3" or 4" PVC, CPVC, polypropylene or stainless steel (Category IV) |
The 230 raises input from 155 to 230 MBH, DOE heating capacity from 139 to 207 MBH and the net AHRI rating from 121 to 180 MBH, and its 94.1% AFUE is the highest DOE rating in the Ultra line — the model behind the CA page's "up to 94.1%" claim.
Venting on the 230 carries a caveat: the manual allows 4" pipe to 100 ft but limits 3" pipe to 30 ft, so a 230 retrofit with an existing 3" route beyond 30 ft cannot use it. The 155, by contrast, runs 3" to a full 100 ft.
Both keep 1" NPT tappings, 5:1 modulation and the 5,500-ft altitude allowance, with water content rising from 1.17 to 1.57 gallons and weight from 234 to 246 lb. The 230 earns its place when the load approaches the 155's 139 MBH of DOE output.
Weil-McLain
The Ultra 155 is the first Series 4 Ultra to require 3" venting: 155 MBH input, 31 MBH low fire, 139 MBH DOE heating capacity and 94.0% AFUE from the cast aluminum condensing block.
Weil-McLain
The Ultra 230 is the most efficient model in the Ultra line at 94.1% AFUE — the figure behind the CA page's up-to-94.1% claim — with 230 MBH input, a 46 MBH low fire and 3"-or-4" venting.
The Ultra 230 at 94.1% AFUE — the figure the CA page's "up to 94.1%" describes. The larger 299 and 399 rate lower (92.5% and combustion efficiency respectively).
Only to 30 ft per the Series 4 manual; a 4" route reaches the full 100 ft.
230 MBH input, 207 MBH DOE heating capacity, 180 MBH net AHRI and 94.1% AFUE.
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 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.