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Comparison
Verdict in brief
Both the Laars Mighty Therm 500 and the Laars Mighty Therm 600 belong to the Laars Heating Systems Mighty Therm (discontinued) line of non-condensing boilers. The Laars Mighty Therm 500 is documented at 500,000 BTU/h input and 405,000 BTU/h output, while the Laars Mighty Therm 600 is documented at 600,000 BTU/h input and 486,000 BTU/h output. Laars Mighty Therm 600 lists 100,000 BTU/h more input than Laars Mighty Therm 500 (600,000 BTU/h against 500,000 BTU/h). Laars Mighty Therm 600 lists 90 lb more shipping weight than Laars Mighty Therm 500 (702 lb against 612 lb).
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Laars Mighty Therm 500 | Laars Mighty Therm 600 |
|---|---|---|
| Input | 500,000 BTU/h | 600,000 BTU/h |
| Output | 405,000 BTU/h | 486,000 BTU/h |
| Shipping weight | 612 lb | 702 lb |
| Water connection | 2" NPT | 2" NPT |
| Gas connection (natural) | 1" NPT | 1" 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 | 357 MBTU/h | 428 MBTU/h |
| Flow at 25°F rise | 31 GPM | 37 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 500 is rated 500,000 BTU/h input and 405,000 BTU/h output; the Laars Mighty Therm 600 is rated 600,000 BTU/h input and 486,000 BTU/h output. Laars Mighty Therm 600 lists 100,000 BTU/h more input than Laars Mighty Therm 500 (600,000 BTU/h against 500,000 BTU/h).
Laars Mighty Therm 600 lists 90 lb more shipping weight than Laars Mighty Therm 500 (702 lb against 612 lb). The flow at 25°F rise differs: the Laars Mighty Therm 500 lists 31 GPM, while the Laars Mighty Therm 600 lists 37 GPM.
Both records print the same water connections (2" NPT), gas connection (1" NPT), electrical requirement (115 V single phase, less than 12 A) and fuel (Natural gas or propane), per the cited sources.
Laars Heating Systems
The Laars Mighty Therm 500 is a discontinued 500,000 BTU/h commercial hydronic boiler (Model HH without a pump or PH pump-mounted) with 405,000 BTU/h output, a 357 MBTU/h IBR net rating and a 612 lb shipping weight per submittal 1053K.
Laars Heating Systems
The Laars Mighty Therm 600 is a discontinued 600,000 BTU/h commercial hydronic boiler (Model HH without a pump or PH pump-mounted) with 486,000 BTU/h output, a 428 MBTU/h IBR net rating and a 702 lb shipping weight per submittal 1053K.
The Laars Mighty Therm 600 lists 600,000 BTU/h, against 500,000 BTU/h on the Laars Mighty Therm 500, per the cited documentation.
The Laars Mighty Therm 600 lists 486,000 BTU/h, against 405,000 BTU/h on the Laars Mighty Therm 500.
It ships at 702 lb against 612 lb for the Laars Mighty Therm 500, 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.