Weil-McLain Ultra 105
The Ultra 105 adds 25 MBH of input over the 80: 105 MBH maximum, 21 MBH low fire, 94 MBH DOE heating capacity and 94.0% AFUE from the same nano-coated cast aluminum Series 4 platform.
Key figures
- Max input
- 105 MBH
- Max CSA output
- 94 MBH
- AFUE
- 94 %
- Min input
- 21 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Weil-McLain Ultra 105 in practice
The Ultra 105 fires from a 21 MBH low fire to 105 MBH maximum CSA input, producing 94 MBH of DOE heating capacity and an 82 MBH net AHRI rating at 94.0% AFUE — a full half-point above the Ultra 80's 93.5%. It is the same 2"-or-3" vented, 1"-tapping platform as the 80, holding 0.82 gallons of water at a 207 lb shipping weight.
The manual notes the 105 derates by up to 15% at a full 100 ft run in 2" pipe, so longer runs favour 3". As a heating-only condensing boiler it pairs with an indirect tank for hot water, and like all Ultras it needs no altitude modification up to 5,500 ft.
Best suited to
- Homes whose heat-loss calculation lands between 80 and 105 MBH
- Buyers who want the efficiency jump from 93.5% to 94.0% AFUE
- Mechanical rooms where a 1"-connected Ultra fits the piping plan
Applicability and support
- Model number
- ULTRA-105
- Canadian availability
- available
- Production status
- current
- ROMA supplies
- Confirmed at consultation
- ROMA services
- Confirmed at consultation
- Warranty
- Series terms
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.
Specifications
Published specifications
Values as published by Weil-McLain. Units are shown with every value; notes flag conflicting sources or missing figures.
| Specification | Value | Note |
|---|---|---|
| Input | ||
| Input, maximum | 105 MBH | CSA input (maximum). |
| Input, minimum | 21 MBH | Low fire (21 MBH) per the Series 4 brochure's CSA input minimum column. |
| Output | ||
| DOE heating capacity | 94 MBH | DOE heating capacity at maximum input; the manuals also call this CSA Output. |
| Net AHRI water rating | 82 MBH | Net AHRI rating per the boiler manual ratings table. |
| Efficiency | ||
| Efficiency (AFUE) | 94 % | 94.0% AFUE. |
| Domestic hot water | ||
| Domestic hot water | Heating-only boiler; domestic hot water via an indirect tank or separate appliance | |
| Venting and air | ||
| Venting | 2" or 3" PVC, CPVC, polypropylene or stainless steel (Category IV) | Canada: install per CAN/CSA B149.1 or B149.2 with a ULC S636-compliant vent kit. |
| Max. equivalent vent/air length | 100 ft in 2" or 3" (derates up to 15% at 100 ft in 2" per the manual) | |
| Physical and connections | ||
| Weight | 207 lb | Approx. shipping weight per the brochure. |
| Gas connection | 1/2" NPT | |
| Heating water connections | 1" NPT | Supply and return tappings 1"; minimum recommended pipe 1". |
| Operating limits and other | ||
| Turndown | 5:1 | 5:1 modulation (20-100% firing rate) per the brochure and CA page. |
| Boiler water content | 0.82 gal | |
| Altitude rating | 5,500 ft | No modifications from sea level to 5,500 ft; the control has a high-altitude selection above 5,500 ft. |
| Fuel | Natural gas or propane | Propane requires a conversion kit per the CA product page. |
Manuals
- Ultra Series 4 Boiler Manual, 550-100-440/1025550-100-440/1025 · 2025-10
Alerts documented for this model
- TEMP RISE TOO QUICKLY
- SUPPLY 58F > RETURN
- RETURN > SUPPLY
- TEMPERATURE SENSOR
- FLUE TEMP TOO HIGH
- TEMPERATURE SENSOR
- LOW WTR CUTOFF OPEN
- DISPLAY COMM
- LIMIT OPEN
- HIGH TEMP LIMIT
- FLAME FAULT
- BLOWER FAULT
- IGNITION FAULT
- GAS VALVE FAULT
- AIR PRESSURE SW FAULT
- GAS PRESSURE SW FAULT
- HW FAULT EXPANSION BRD
- GV FAULT EXPANSION BRD
- EXP BOARD COM FAULT
Frequently asked questions
How does the Ultra 105 differ from the Ultra 80?
Input rises from 80 to 105 MBH, low fire from 16 to 21 MBH, DOE heating capacity from 71 to 94 MBH, and AFUE from 93.5% to 94.0%.
Can the Ultra 105 vent in 2" pipe?
Yes, to 100 ft — but the manual warns of up to 15% derate at a full 100 ft run in 2", so long runs favour 3" pipe.
Is the Ultra 105 suitable for radiant floors?
The Ultra is designed for low-temperature condensing operation, and outdoor reset control supports low water temperatures; a heat-loss and system design check decides suitability.
Questions about the Weil-McLain Ultra 105?
Describe what the boiler is doing and get a straight answer about the next step.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Compare and explore
- Weil-McLain Ultra 80 vs Ultra 105Comparison
- Weil-McLain Ultra 105 vs Ultra 155Comparison
- Weil-McLain Ultra 80Same series
- Weil-McLain Ultra 155Same series
- Weil-McLain Ultra 230Same series
- Weil-McLain Ultra 299Same series
- Weil-McLain Ultra 310Same series
- Weil-McLain Ultra 399Same series
- Ultra series hub
- Buying guide
Sources and verification
- Weil-McLain Canada — Ultra · accessed September 7, 2026
- Ultra Series 4 Boiler Manual 550-100-440/1025 · 550-100-440/1025 · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.