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Comparison
Verdict in brief
The Laars Mighty Therm 715 and Laars Mighty Therm 850 are both non-condensing boilers in the Laars Heating Systems Mighty Therm (discontinued) line. Published ratings: Laars Mighty Therm 715 at 715,000 BTU/h input and 579,150 BTU/h output; Laars Mighty Therm 850 at 850,000 BTU/h input and 688,500 BTU/h output. Laars Mighty Therm 850 lists 135,000 BTU/h more input than Laars Mighty Therm 715 (850,000 BTU/h against 715,000 BTU/h). Laars Mighty Therm 850 lists 80 lb more shipping weight than Laars Mighty Therm 715 (830 lb against 750 lb).
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Laars Mighty Therm 715 | Laars Mighty Therm 850 |
|---|---|---|
| Input | 715,000 BTU/h | 850,000 BTU/h |
| Output | 579,150 BTU/h | 688,500 BTU/h |
| Shipping weight | 750 lb | 830 lb |
| Water connection | 2" NPT | 2" NPT |
| Gas connection (natural) | 1" NPT | 1-1/4" NPT |
| Electrical | 115 V single phase, less than 12 A | 115 V single phase, less than 12 A |
| Fuel | Natural gas or propane | Natural gas or propane |
| IBR net rating | 510 MBTU/h | 606 MBTU/h |
| Flow at 25°F rise | 45 GPM | 53 GPM |
| Pump (PH models) | 1/3 HP, 2.8 A | 1/3 HP, 2.8 A |
| Altitude | De-rate 4% per 1,000 ft above 2,000 ft | De-rate 4% per 1,000 ft above 2,000 ft |
Published ratings: the Laars Mighty Therm 715 is rated 715,000 BTU/h input and 579,150 BTU/h output; the Laars Mighty Therm 850 is rated 850,000 BTU/h input and 688,500 BTU/h output. Laars Mighty Therm 850 lists 135,000 BTU/h more input than Laars Mighty Therm 715 (850,000 BTU/h against 715,000 BTU/h).
Laars Mighty Therm 850 lists 80 lb more shipping weight than Laars Mighty Therm 715 (830 lb against 750 lb). The gas connection differs: the Laars Mighty Therm 715 lists 1" NPT, while the Laars Mighty Therm 850 lists 1-1/4" NPT. The flow at 25°F rise differs: the Laars Mighty Therm 715 lists 45 GPM, while the Laars Mighty Therm 850 lists 53 GPM.
Both records print the same water connections (2" NPT), electrical requirement (115 V single phase, less than 12 A), fuel (Natural gas or propane) and pump (1/3 HP, 2.8 A), per the cited sources.
Laars Heating Systems
The Laars Mighty Therm 715 is a discontinued 715,000 BTU/h commercial hydronic boiler (Model HH without a pump or PH pump-mounted) with 579,150 BTU/h output, a 510 MBTU/h IBR net rating and a 750 lb shipping weight per submittal 1053K.
Laars Heating Systems
The Laars Mighty Therm 850 is a discontinued 850,000 BTU/h commercial hydronic boiler (Model HH without a pump or PH pump-mounted) with 688,500 BTU/h output, a 606 MBTU/h IBR net rating and a 830 lb shipping weight per submittal 1053K.
The Laars Mighty Therm 850 lists 850,000 BTU/h, against 715,000 BTU/h on the Laars Mighty Therm 715, per the cited documentation.
The Laars Mighty Therm 850 lists 688,500 BTU/h, against 579,150 BTU/h on the Laars Mighty Therm 715.
It ships at 830 lb against 750 lb for the Laars Mighty Therm 715, per the cited sources.
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.