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 FTXL FTX725 and FTX850 share every connection — 2-1/2" water, 1" gas, 4" air and 6" vent at 7:1 turndown — and differ in capacity: the 850 fires 121.4 to 850 MBH with 825 MBH gross output, while its submittal efficiency eases to 97.0%.
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Lochinvar FTXL FTX725 | Lochinvar FTXL FTX850 |
|---|---|---|
| Heating input, minimum | 103.6 MBH | 121.4 MBH |
| Heating input, maximum | 725 MBH | 850 MBH |
| Gross output | 705 MBH | 825 MBH |
| Net AHRI water rating | 613 MBH | 717 MBH |
| Efficiency (thermal) | 97.2 % | 97 % |
| Water content | 17.2 gal | 15.9 gal |
| Space-heating water connections | 2-1/2" | 2-1/2" |
| Gas connection | 1" | 1" |
| Air inlet size | 4" | 4" |
| Vent size | 6" | 6" |
| Shipping weight | 575 lb | 604 lb |
The FTX725 and FTX850 are the closest pair in the FTXL Series 120 range: the I&O ratings table lists the same 2-1/2" water connections, 1" gas connection, 4" air intake and 6" vent for both, and the submittal rates both at 7:1 turndown.
The step is capacity: maximum input rises from 725 to 850 MBH, gross output from 705 to 825 MBH and the AHRI net rating from 613 to 717 MBH, while the minimum fire rises from 103.6 to 121.4 MBH.
Water content falls from 17.2 to 15.9 gallons at the 850 and shipping weight rises from 575 to 604 lb per the submittal. Submittal thermal efficiency eases from 97.2% to 97.0% — the lowest figure in the FTXL line — so a load that fits the 725 leaves efficiency and part-load behavior on the table at the 850.
Lochinvar
The FTXL FTX725 fires 103.6 to 725 MBH with 705 MBH gross output and a 613 MBH AHRI net rating at 97.2% submittal thermal efficiency, stepping to 2-1/2" water connections and a 6" vent.
Lochinvar
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.
The FTX725: 97.2% submittal thermal efficiency against the FTX850's 97.0%, which is the lowest per-model figure in the FTXL line.
Yes — both list 2-1/2" water connections, 1" gas, 4" air and 6" vent per the I&O ratings table; only capacity, water content and weight differ.
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.