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Comparison
Verdict in brief
Both the Laars Mighty Therm2 MT2V0300 and the Laars Mighty Therm2 MT2H0400 belong to the Laars Heating Systems Mighty Therm2 line of non-condensing boilers. The Laars Mighty Therm2 MT2V0300 is rated 300,000 BTU/hr input, 255,000 BTU/hr output and 85% thermal efficiency, and the Laars Mighty Therm2 MT2H0400 is rated 399,000 BTU/hr input, 340,000 BTU/hr output and 85.3% thermal efficiency. Laars Mighty Therm2 MT2H0400 lists 99,000 BTU/hr more input than Laars Mighty Therm2 MT2V0300 (399,000 BTU/hr against 300,000 BTU/hr). Laars Mighty Therm2 MT2H0400 carries the higher published thermal efficiency at 85.3%, against 85%. Laars Mighty Therm2 MT2H0400 lists 30 lb more shipping weight than Laars Mighty Therm2 MT2V0300 (330 lb against 300 lb).
Published manufacturer figures. Input and output are kept separate; blanks mean the manufacturer did not publish that value.
| Specification | Laars Mighty Therm2 MT2V0300 | Laars Mighty Therm2 MT2H0400 |
|---|---|---|
| Input | 300,000 BTU/hr | 399,000 BTU/hr |
| Output | 255,000 BTU/hr | 340,000 BTU/hr |
| Efficiency (thermal) | 85 % | 85.3 % |
| Shipping weight | 300 lb | 330 lb |
| Water connection | 1-1/2" | 1-1/2" |
| Gas connection | 3/4" | 3/4" |
| Firing | Two-stage, up to 4:1 | Two-stage, up to 4:1 |
| Venting | Category I fan-assisted; Category III with a listed vent system | Category I fan-assisted; Category III with a listed vent system |
Published ratings: the Laars Mighty Therm2 MT2V0300 is rated 300,000 BTU/hr input, 255,000 BTU/hr output and 85% thermal efficiency; the Laars Mighty Therm2 MT2H0400 is rated 399,000 BTU/hr input, 340,000 BTU/hr output and 85.3% thermal efficiency. Laars Mighty Therm2 MT2H0400 lists 99,000 BTU/hr more input than Laars Mighty Therm2 MT2V0300 (399,000 BTU/hr against 300,000 BTU/hr). Laars Mighty Therm2 MT2H0400 carries the higher published thermal efficiency at 85.3%, against 85%.
Laars Mighty Therm2 MT2H0400 lists 30 lb more shipping weight than Laars Mighty Therm2 MT2V0300 (330 lb against 300 lb).
Both records print the same water connections (1-1/2"), gas connection (3/4"), firing (Two-stage, up to 4:1) and venting (Category I fan-assisted; Category III with a listed vent system), per the cited sources.
Laars Heating Systems
The Laars Mighty Therm2 MT2V0300 is a non-condensing volume water heater rated 300,000 BTU/hr input and 255,000 BTU/hr output at 85% thermal efficiency.
Laars Heating Systems
The Laars Mighty Therm2 MT2H0400 is a non-condensing commercial hydronic boiler rated 399,000 BTU/hr input and 340,000 BTU/hr output at 85.3% thermal efficiency.
The Laars Mighty Therm2 MT2H0400 lists 399,000 BTU/hr, against 300,000 BTU/hr on the Laars Mighty Therm2 MT2V0300, per the cited documentation.
The Laars Mighty Therm2 MT2H0400 carries the higher published thermal efficiency at 85.3%, against 85%.
It ships at 330 lb against 300 lb for the Laars Mighty Therm2 MT2V0300, 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.