Smith Cast Iron Boilers · GBX Series (discontinued)
Smith GBX-105
The Smith GBX-105 is a discontinued residential cast-iron water boiler rated 105 MBH AGA input with 86 MBH DOE heating capacity, 75 MBH net I=B=R and 82.1% AFUE, on 1-1/2" supply and 1-1/4" return tappings.
Key figures
- Max input
- 105 MBH
- Max CSA output
- —
- AFUE
- 82.1 %
- Min input
- —
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Smith GBX-105 in practice
The GBX-105 is one of the GBX sizes in Smith's discontinued residential cast-iron water boiler line. The BSG-10 selection guide prints 105 MBH AGA input, 86 MBH DOE heating capacity, 75 MBH net I=B=R water and 82.1% AFUE; the GBXIOM-4 manual's Table 10.2 prints the same ratings and adds a 6 gal water content for this size.
GBXIOM-4 instructs piping the supply to the 1-1/2" NPT tapping at the top and rear of the boiler and the return to the 1-1/4" NPT tapping near the bottom of the left section. The line is natural gas or propane with intermittent ignition. Smith's official navigation marks the GBX '(Discontinued)', so the model is recorded for legacy reference with productStatus discontinued.
Best suited to
- Legacy GBX owners looking up printed ratings for service or replacement comparison
- Replacement planning where the existing GBX size must be matched against a current boiler
Applicability and support
- Model number
- GBX-105
- Canadian availability
- unknown
- Production status
- discontinued
- ROMA supplies
- Confirmed at consultation
- ROMA services
- Confirmed at consultation
- Warranty
- Not verified
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 Smith Cast Iron Boilers. Units are shown with every value; notes flag conflicting sources or missing figures.
| Specification | Value | Note |
|---|---|---|
| Input | ||
| AGA input (as printed) | 105 MBH | AGA input printed in BSG-10. |
| Output | ||
| DOE heating capacity | 86 MBH | BSG-10 and GBXIOM-4 Table 10.2 agree on 86 MBH. |
| Net I=B=R water rating | 75 MBH | Printed in BSG-10 (allowance 1.15 per the manual's notes). |
| Efficiency | ||
| AFUE | 82.1 % | Printed in BSG-10. |
| Physical and connections | ||
| Supply / return tappings | 1-1/2" NPT supply / 1-1/4" NPT return | GBXIOM-4: supply tapping at the top and rear of the boiler; return tapping near the bottom of the left section. |
| Water content | 6 gal | GBXIOM-4 Table 10.2 prints water content for each GBX size. |
| Operating limits and other | ||
| Fuel | Natural gas or propane | BSG-10: 'available in five sizes ranging from 70 to 195 MBH in both natural and propane gas with intermittent ignition systems'. |
Manuals
Alerts documented for this model
None documented yet.
Frequently asked questions
Is the Smith GBX-105 still made?
No. Smith's official site navigation marks the GBX line '(Discontinued)'. The BSG-10 selection guide and GBXIOM-4 manual remain public for legacy reference.
What are the GBX-105 ratings?
BSG-10 prints 105 MBH AGA input, 86 MBH DOE heating capacity, 75 MBH net I=B=R water and 82.1% AFUE.
Questions about the Smith GBX-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.
Sources and verification
- Smith Cast Iron Boilers — home (nav marks GBX '(Discontinued)') · accessed September 9, 2026
- Smith — Boiler Selection Guide BSG-10 (GBX/GVX specifications) · BSG-10 · accessed September 9, 2026
- Smith — GBX Gas-Fired Residential Boilers manual GBXIOM-4 (Table 10.2 ratings, supply/return tappings) · GBXIOM-4 · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.