Lochinvar FTXL FTX850
The FTXL FTX850 fires 121.4 to 850 MBH with 825 MBH gross output and a 717 MBH AHRI net rating at 97.0% submittal thermal efficiency, on 2-1/2" water connections with 6" venting.
Key figures
- Max input
- 850 MBH
- Max CSA output
- —
- AFUE
- —
- Min input
- 121.4 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Lochinvar FTXL FTX850 in practice
The FTX850 is the top of the FTXL Series 120 range: the I&O ratings table lists 121.4 to 850 MBH input with 825 MBH gross output and a 717 MBH AHRI net water rating at 97.0% submittal thermal efficiency — the lowest per-model figure in the FTXL line per the submittal. Its 15.9-gallon water content sits on 2-1/2" water and 1" gas connections with a 4" air intake and 6" vent.
Turndown is 7:1 per the submittal, matching the 121.4 MBH minimum input against the 850 MBH maximum. It vents in PVC, CPVC, polypropylene or AL29-4C stainless steel to 100 equivalent feet per the submittal and carries the family's SMART TOUCH control with CON·X·US, ASME H stamp and stainless steel fire-tube heat exchanger; the submittal lists a 604 lb shipping weight.
Best suited to
- Commercial loads between 725 and 850 MBH on a design day
- Larger light-commercial buildings in the FTXL's 399,000-999,000 BTU/hr territory
- Plants sized for 2-1/2" water piping with a 6" vent
Applicability and support
- Model number
- FTX850N
- 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 Lochinvar. Units are shown with every value; notes flag conflicting sources or missing figures.
| Specification | Value | Note |
|---|---|---|
| Input | ||
| Heating input, minimum | 121.4 MBH | Per the I&O ratings table. |
| Heating input, maximum | 850 MBH | Per the I&O ratings table. |
| Output | ||
| Gross output | 825 MBH | Per the I&O ratings table. |
| Net AHRI water rating | 717 MBH | Per the I&O ratings table. |
| Efficiency | ||
| Efficiency (thermal) | 97 % | 97.0% thermal efficiency per the FTXL submittal. |
| Venting and air | ||
| Air inlet size | 4" | Per the I&O ratings table. |
| Vent size | 6" | Per the I&O ratings table. |
| Venting | Category IV sealed combustion; room air/direct vent in PVC, CPVC, polypropylene or AL29-4C stainless steel | Direct vent to 100 equivalent feet per the FTXL submittal and the product-page feature list; common vent kit available. |
| Physical and connections | ||
| Water content | 15.9 gal | Per the I&O ratings table. |
| Space-heating water connections | 2-1/2" | Per the I&O ratings table. |
| Gas connection | 1" | Per the I&O ratings table. |
| Shipping weight | 604 lb | Shipping weight per the FTXL submittal. |
Manuals
Alerts documented for this model
- Gas Pressure SW
- Flow Switch/LWCO
- Blocked Drain SW
- Anti-cycling
- Flame Fail Ign
- Flame Sequence
- Outlet ARHL
- Outlet MRHL
- Fan Low/High OR Fan Speed Low/High
- Sensor Open
- Sensor Shorted
- Louver Proving Sw
- Inlet Sensor Fault
- Outlet Sensor Fault
- Outlet Temp Diff
- Flue Sensor Fault
- Flue Temp Diff
- Flue Temp Limit
- Fatal Error
- Memory Error
- Flue Temp High
- Delta T High
- Outlet Temp High
- Rem Ctrl Flt
- Parameters Progr
- Service Blk
- Low 24 vac
- Watch Dog Error
- Write EEProm
- CRC Parameters
- No Error Stored
Frequently asked questions
What are the FTX850's ratings?
121.4 to 850 MBH of input with 825 MBH gross output and a 717 MBH AHRI net water rating at 97.0% thermal efficiency per the FTXL submittal.
How does the FTX850 compare with the FTX725?
Maximum input rises from 725 to 850 MBH and gross output from 705 to 825 MBH, while water content falls from 17.2 to 15.9 gallons; connections stay 2-1/2" water, 1" gas, 4" air and 6" vent.
Questions about the Lochinvar FTXL FTX850?
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
- Lochinvar — FTXL Fire Tube Boiler (FTX400N) model page · accessed September 9, 2026
Facts checked September 9, 2026. Last updated September 9, 2026. Technical reviewer: not yet assigned.