What it is
The Firman H03655 is a mid-size open-frame dual-fuel generator built around a 208cc engine with a cast iron cylinder sleeve. It delivers 3,650 running watts and 4,550 starting watts on gasoline, or 3,300 running watts and 4,100 starting watts on propane, with a 5-gallon tank running up to 14 hours at a half load. Firman is a newer brand to this review series, and this model fills a real gap: a straightforward conventional generator between the small inverters and the whole-home dual-fuel units already covered here.
The control panel includes a TT-30R RV outlet along with standard household outlets, a fuel-selector switch for choosing between gas and propane, and a recoil pull start. Rolling on an 8-inch never-flat wheel kit with a folding handle, it weighs about 112 pounds, so this is a generator that gets wheeled into place rather than carried. It ships EPA compliant.
Why it works
This generator earns its place with a straightforward set of real advantages:
CO Alert built in as standard
This model ships with Firman's CO Alert system, which monitors carbon monoxide levels near the unit and automatically shuts the engine down before they become dangerous. Unlike some budget brands where CO protection is reserved for a pricier variant, it comes standard here.
Real fuel flexibility
Gasoline or propane, switchable with a single control, means you are not dependent on one fuel source during an extended outage. Propane stores indefinitely without the stabilizer routine gasoline requires, which matters for a generator that might sit unused for months between needs.
Priced for a straightforward workhorse role
This is a conventional generator, not an inverter, which keeps the price well below inverter models with similar wattage. For a household that mainly needs to run a refrigerator, some lights, and a window unit during an outage, that tradeoff is usually the right one.
The one thing to know
Carbon monoxide safety is non-negotiable
Portable generators produce carbon monoxide, an odorless gas that can reach lethal concentrations indoors within minutes. The CPSC recommends placing any portable generator at least 20 feet from all doors, windows, and vents, with the exhaust pointed away from the home. Never run a generator indoors, in a garage, on a covered porch, in a carport, or in any enclosed or partially enclosed space, even with doors or windows open. This unit's CO Alert system provides a backup layer of protection if levels near the generator rise, but it is not a substitute for correct placement. Install battery-operated CO detectors on every level of your home.
Source: CPSC Carbon Monoxide Information Center and CDC generator safety guidance. Verified 2026-08-05.
The other thing to know is that this is not clean inverter power. Total harmonic distortion runs well above what is considered safe for laptops, phones, and other sensitive electronics without added protection, so treat this as a generator for appliances and lighting rather than a direct line to your electronics. It is also a genuine two-hands-on-the-handle generator at 112 pounds; the wheel kit helps on flat ground, but this is not something one person carries up stairs.
Alternatives worth knowing
Champion 4,750W Dual-Fuel, for more running watts
More running wattage (3,800W) at a similar price point, also with CO Shield built in. The right choice if you need a bit more headroom for appliances running at the same time. Read our review.
Westinghouse WGen5300DFc, for a step up in capacity
Substantially more running wattage (5,300W) with a transfer-switch outlet, at a higher price. The right choice if you are planning around a transfer switch and want more panel coverage. Read our review.
DuroMax XP2300iH, for clean inverter power
Less running wattage (1,800W) but genuinely clean sine-wave power safe for sensitive electronics, also dual fuel. The right choice if you need to run laptops or medical devices directly off the generator. Read our review.
Maintenance
Run the generator under load for 15 to 30 minutes every 30 days to keep the engine and fuel system in working order. Add fuel stabilizer to the tank for any storage period longer than 30 days when running on gasoline; propane storage does not require this step.
Check the oil level before every use. Follow the manual's schedule for oil change intervals, and inspect the air filter and spark plug annually.
Firman backs the H03655 with a 3-year warranty. Register the unit and keep the purchase receipt with your household documents.
NWS recommendation
If you want a mid-size dual-fuel generator that covers a refrigerator, a window unit, and lights without paying inverter prices, and you want carbon monoxide protection built in, the H03655 does the job. If clean power for electronics matters more than price, compare it against an inverter model first. Test it before you need it, and place it at least 20 feet from the house with the exhaust pointed away.
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