The choice between an electric and a gas pressure washer is usually framed as a power question. It is more accurately a flow question, a maintenance question, and above all a ventilation question. One of those three has consequences that are not recoverable, so it belongs first.
The carbon monoxide rule comes before every other consideration
A gas pressure washer is powered by an internal combustion engine, and that engine produces carbon monoxide. Carbon monoxide is colorless, odorless, and lethal at concentrations that give no warning. A gas pressure washer must never be run indoors, in a basement, in a crawl space, in a carport, or in a garage. That includes a garage with the door open. An open door does not create adequate ventilation, and manufacturer manuals say so in the strongest terms they use anywhere in the document.
This applies to every engine driven unit in the gas powered listings, whatever the engine size. The 208cc engine on the DeWalt 61147S and the 224cc engine on the BILT HARD 3500 PSI unit are subject to the identical restriction. Corded electric machines produce no combustion exhaust, and for anyone who has to work in a garage, a warehouse bay, or any partially enclosed space, that fact alone settles the decision.
The real difference is water flow
Both categories reach similar pressures. Where they separate is gallons per minute, because a corded machine is limited by what a household circuit can deliver and an engine is not.
The gas units in this catalog publish flow figures between roughly 2.4 and 4.0 GPM. The Simpson ALH4440 is at the top of that range at a listed 4.0 GPM. The Westinghouse WPX3400 is described as 3,400 PSI and 2.6 max GPM from a 212cc four stroke engine, and the Simpson CM61083 as 3,400 PSI at 2.5 GPM from a 208cc engine.
Corded machines in the electric pressure washer listings mostly sit between 1.1 and 2.3 GPM. The Greenworks GPW2300, listed at 2,300 PSI and 2.3 GPM and described as PWMA certified, is near the ceiling of what a 120 volt appliance can sustain. The Sun Joe SPX3001 publishes the constraint plainly: a 14.5 amp, 1,800 watt motor on 120 volts. That is close to the practical limit of a standard 15 amp branch circuit.
The consequence is throughput. On a long driveway or a large patio, a machine delivering 2.5 GPM covers ground far faster than one delivering 1.2 GPM, regardless of which one carries the higher PSI number on the box. On a car, a set of patio furniture, or a small deck, that advantage largely disappears.
Pump construction separates the gas machines from each other
Gas listings in this catalog use two pump architectures, and the distinction affects service life more than the PSI rating does.
An axial cam pump is compact, sealed, and described in these listings as maintenance free, which in practice means it is not intended to be rebuilt. The DeWalt 61147S, the Westinghouse WPX3400, and the DeWalt DXPW3400PRNB-S all use axial cam pumps.
A triplex plunger pump runs cooler, turns at lower speed, and is generally serviceable. The Simpson ALH4440 listing specifies a CAT industrial triplex plunger pump, and the Simpson ALH3425 listing specifies an AAA industrial triplex plunger pump behind a Honda GX200 engine. Buyers planning long sessions rather than occasional weekend use should weigh that difference, because a pump that cannot be rebuilt sets a ceiling on the useful life of the whole machine.
A note on how these figures are published
Gas listings are not immune to the numbers problem. The Simpson ALH4440 title states 4,400 PSI at 4.0 GPM and then, in the same title, states 4,200 PSI. Both figures appear on the manufacturer listing and there is no explanation of which is the rated working pressure. Similarly, the PowerSmart DB1051 listing advertises 3,200 PSI and 2.5 GPM in its description while its specification table records 5 gallons per minute, which is almost certainly an inlet supply requirement that has been entered in the wrong field. Where two figures exist, both belong in front of a reader.
What each side actually costs the owner
A gas machine adds fuel, oil changes, a pull start, winter fuel stabilization, and noise loud enough to make hearing protection sensible. It also adds weight. Against that it offers flow, independence from an outlet, and pumps that can outlast the buyer’s interest in cleaning.
A corded electric machine adds a tether. It needs a suitable outlet, it typically ships with a 35 foot power cord and an inline ground fault circuit interrupter, and manufacturers commonly restrict or prohibit extension cord use. It starts with a switch, it makes far less noise, and it can be stored in a closet. It cannot be used where there is no power.
Where the catalog labels do not match the machines
Three listings on this site are filed under a category that does not describe the machine, and readers browsing by category should know it. The Simpson ALH3425, listed with a Honda GX200 gas engine at 3,600 PSI and 2.5 GPM, and the Westinghouse WPX3200, listed with a 212cc four stroke gas engine at 3,200 PSI and 2.5 max GPM, are both filed with the electric machines. Both are gas units and both carry the full carbon monoxide restriction: never indoors, never in a garage, not even with the door open.
The reverse also occurs. The Karcher K1800PS Cube is filed with the gas machines, but the listing describes an electric unit rated at 1,800 PSI with no engine at all.
Choosing between them
The decision usually resolves on three questions. Is there any chance the machine will need to run in or near an enclosed space? If yes, the answer is electric, and the question ends there. Is the recurring job a large flat area measured in hundreds of square feet? If yes, flow matters and gas earns its complexity. Is the machine going to be used a handful of times a year on a car, a deck, and some furniture? If yes, a corded machine at 1.2 to 2.0 GPM will do the work with less to maintain.
Safety rules that apply on both sides
Pressure at these levels is dangerous regardless of what drives the pump. The jet must never be aimed at a person or an animal. A high pressure stream can drive water, dirt and bacteria through skin, producing an injection injury that can look like a small puncture while causing severe damage below the surface. Any suspected injection injury is a medical emergency and needs immediate assessment, not a bandage. Eye protection, closed footwear and a firm two handed grip on the wand are standard manufacturer instructions. The manual supplied with the specific machine governs, and where it conflicts with anything written here, the manual wins.
