When you're on the job framing a house there's nothing worse than having to wait for your compressor to play catch-up. Those days are likely over with the Bosch CET4-20W 4 Gallon Electric Hand Carry Compressor with wheels. Not only is this a convenient tool to carry around, it's got the volume and fast recovery time to make sure you can keep working, uninterrupted, no matter what the job. We used the CET4-20W on a variety of jobs and it held its own each time, earning it the nickname "Jack" – as in "be nimble and quick."

We've used many different air compressors over the years, from hot dog style to pancake and even 8-gallon wheeled models that provide a large volume of air. Nothing, in our opinion, beats a nice compact twin-stack for all around usefulness. While not exactly compact, the Bosch twin stack is convenient in that it presents itself as an easily portable solution that packs a punch. Bosch's take on this design improves it further by offering 4 gallons of air capacity and wheels for easy transport. They also mount the tanks vertically, something unique that allows both tanks to drain simultaneously. Because this is a heavier-duty model, be aware that it weighs in at around 85 pounds, making it one of the heavier units (by roughly ten pounds) we've tested. This is no simple trim compressor!

Build Quality

The CET4-20W 4 gallon Compressor comes in the expected Bosch Blue. The tanks are welded steel and are oriented vertically, which makes draining easy. The engine is an electric 2 horsepower model that sits within a steel roll cage which protects it from the hazards of jobsite use. The air compressor is oil-lubricated to keep the parts from premature wear. You literally have tubular steel surrounding all of the sensitive parts. It ships filled with oil and the cap includes an integrated dipstick for checking levels every 200 hours of use. The system comes with the wheels detached so the first thing we did was attach them using the included bolt washers and nut. The entire compressor weighs nearly 85 pounds, making it quite heavy to lift. The wheels, however make it easy to port this tool around and all but eliminate the need to pick it up, save unloading it from your truck or work van.

The wheels go on such that the inflation stems are located on the inside. You can (barely) reach them using the backside of a standard tire inflation adapter, but they would be more accessible on the outside of the wheels. We found this out the hard way when a friend (who shall remain nameless because I want to hold this over his head for a while longer) rolled all 85 pounds off the side of an 8" tall deck. One of the wheels lost its seal and we had to re-inflate it. Other than inserting the oil dipstick/cap there is no further assembly required to get the CET4-20W up and running.

The integrated handle swings up and locks in place to allow you to easily cart the compressor around the jobsite. What we noticed, however, was that the locking pin was very shallow. In addition, there was only one, whereas we would expect there to be one on each side of the handle. This made the handle a bit unsteady in its upright position, something that you don't want in a tool that is otherwise very ruggedly built. After inquiring with Bosch, we found that the locking mechanism hadn't been fully threaded into the steel plate. Once we bottomed it out, the pin inserted fully into the hole and we concurred with Bosch that the single pin was probably just as good, in terms of stability, as using two.

Between the tanks lie the twin pressure gauges, one for the tank PSI and the other for the outlet PSI. The pressure regulator control is between and below this assembly are the twin outlet fittings. The pressure regulator was very hard to turn at first, but once we broke it free it worked as expected. Having two outlet fittings means you can use two pneumatic tools at once, or simply keep two tools connected so you don't have to reconnect when, for example, you switch from a framing nailer to a roofing coil nailer. We were also pleased to find these sensitive controls and couplers partially recessed within the tanks. That provided them ample protection during use and meant that we were unlikely to accidentally damage them on the job. At the very bottom of the regulator assembly you'll find the tank drain valve, which we thought was very well designed and easy to use. After pulling the safety release valve to drop the tank pressure down to 20 PSI or below, this drain valve easily allows air and condensation to drain from both of the vertically-positioned tanks at the same time. I try to drain my tanks daily unless they are kept indoors where I can get a bit more use out of them before they build up with condensation.

The air compressor pump looks to be ruggedly built and the oiled system ensured a quieter operation than typical Teflon coated or other oil-free systems. The major heat-prone areas of the motor are covered with ABS plastic and thus protect somewhat from the ability to inflict accidental burns, should you venture too close. The pressure switch cover was easily removed and you can set the limits of when the compressor will stat to refill as well as the maximum pressure to which it will charge the tanks. The hoses used to route air from the tanks to the regulator and outlet fittings is rugged, with a thick wall that isn't likely to give you any problems over time. In fact, I'd have to say that in taking a look at this compressor in comparison with our other models we've used it's got to be one of the more well-built products we've seen on the market. This isn't a casual-use tool. With a 12-second recovery time, 4.9 CFM rate, and 4 gallons of air storage, the CET4-20W is a tool that can go all day long in framing applications without breaking much of a sweat. Those looking for a constant-use flow of air will, of course, want to either check out one of Bosch's Wheelbarrow compressors or a larger capacity vertical air compressor.

In the Field

We used the Bosch CET4-20W hard. From framing a deck, to putting up walls for a Habitat for Humanity home, we ran it through its paces in almost every conceivable way that it was designed for. In our Habitat project, it was paired with a Bosch Full Head Angled Framing Nailer SN350-20F which we were able to dial in perfectly for both framing and sheathing. The consistency of the pressure, meant that the depth adjustment dial could be used – as designed – to perfectly set the nail as needed. But what we really appreciated was the infrequent recoveries and consistency that the CET4-20W offered. It was also nice for us to be able to simply lower the compressor off our work truck and quickly roll it into position without having to break our backs lugging the tool to our staging position. Hose connections were quick and easy and the cord was long enough that it gave us some flexibility in moving it around without yanking on all our other tools that were connected to the same breakout box.

In using two nailers at once, the compressor had to recover more often, but the 4 gallons definitely made a difference and we found that we could all but disregard the compressor and just get to work. It was nice not having to slow down or worry about it catching up to us. Every nail fired smoothly and the supply seemed consistent with what our tools were expecting. You can actually dial the pressure switch in to alter the recovery cycles, allowing for more leniency (lower pressure) between when the pump kicks in, or holding the compressor to a tighter standard where your tools maintain higher PSI. We configured it close to its defaults, where the CET4-20W would find itself turning on at around 95 PSI and charging up to 120 PSI.

Conclusions & Recommendations

This is a great compressor for professionals and homeowners alike. What makes it especially good, aside from its excellent portability and wheeled frame, is the ruggedness of the tool and its ability to quickly recover air. Twelve seconds is a fast recovery time for a tool of this size and the balance of fast recovery to tank size is an important one. Bosch seems to knock it out of the park with the CET4-20W. Those looking to use this in a daily contractor's role will appreciate the attention to detail, low noise, integrated protection provided by the recessing of the controls, and the all-steel cage that virtually surrounds the motor. At a street price of less than $350, this tool is a great value as reflected by our 8/10 Value rating. If you can't already tell, its performance blew us away and we only dinged it for what we feel are some minor quality control issues, earning it a 9/10. Heartily recommended!