When you are unsure, start wider and gentler. A narrow spray concentrates force into a smaller area, which can clean faster but can also damage paint, soft wood and other surfaces faster.
0-degree tip: very concentrated
This is the pencil-like stream. On the ePX3500, Westinghouse groups the 0-degree and turbo nozzles as high-pressure choices and tells users to use appropriate nozzles to avoid surface damage.
15-degree tip: strong but spread out
This is a common step down from the most concentrated stream. It can be useful on tougher outdoor surfaces where you still want a defined fan.
25-degree tip: a gentler general-cleaning starting point
For many ordinary cleaning jobs, a wider fan is easier to control. You can adjust effective cleaning force by changing your distance from the surface.
Turbo nozzle: fast cleaning, but still aggressive
A turbo tip moves a concentrated stream rapidly in a circular pattern. It can be excellent on hard, durable surfaces, but it is not a free pass to use it on anything dirty.
Soap nozzle: detergent, not blasting
On the ePX3500, the soap nozzle is the low-pressure detergent applicator. If your soap will not draw, this is the first thing to check.
Use the soap troubleshooting guide.
Westinghouse tells users to test in a small, inconspicuous area. That is good advice on any surface where damage would bother you.
Think in terms of force per area
The narrower the fan, the more concentrated the cleaning force. Increasing your distance from the surface spreads the force out and usually makes the spray gentler. Those two controls, nozzle angle and distance, matter more than memorizing nozzle colors.
Start with the job, not the stain
A dirty painted fence and a dirty concrete slab are both dirty, but they should not automatically get the same nozzle. Ask what the surface can safely tolerate before asking how stubborn the dirt is.
When a nozzle set is a good purchase
If your original tips are missing, damaged or hard to identify, a clearly labeled compatible set can make the washer much easier to use. Match the quick-connect size and the nozzle orifice requirements for your machine.
Sources used for this answer
Back to class: Electric Pressure Washer Class.