What Do Professionals Use to Pressure Wash Houses? Tools, Machines, and Techniques Explained

When you see a house that looks like it just got a fresh coat of paint-except it didn’t-chances are, it was pressure washed. The dirt, mold, algae, and years of grime vanish in minutes. But what’s actually in the hands of the pros doing this job? It’s not just a garden hose with a nozzle. Professionals use specific tools, machines, and techniques that turn a messy chore into a precise, safe, and effective cleaning process.

What Professionals Actually Use

Most professional pressure washers in the UK use gas-powered machines rated between 3,000 and 4,000 PSI (pounds per square inch). That’s three to four times stronger than a typical home unit you can rent or buy from a hardware store. Why? Because house surfaces like brick, stucco, and concrete need enough force to lift embedded dirt without damaging the material. Too little pressure, and you waste time. Too much, and you strip paint, gouge wood, or crack siding.

These machines also run at 3 to 4 GPM (gallons per minute). Flow rate matters as much as pressure. A machine with high PSI but low GPM will struggle to rinse away loosened grime. Professionals need volume to flush out debris quickly. That’s why rental units often feel underpowered-they’re designed for light use, not full-day jobs.

Brands like Karcher, Hotsy, and NorthStar dominate professional job sites. These aren’t just names-they’re trusted for durability, parts availability, and consistent performance. A pro might spend £1,500 to £3,000 on a machine, not because they’re extravagant, but because a cheap unit breaks down after three jobs, costing more in downtime and replacements.

Nozzle Types and Their Roles

Pressure washers come with interchangeable nozzles, and pros know exactly which one to use for each surface. The nozzle isn’t just a tip-it’s the control center.

• 0° nozzle: A thin, focused stream. Used only for stubborn stains on concrete driveways or removing paint from metal. Never used on house siding-it’ll chip or cut into surfaces.
• 15° nozzle: The go-to for cleaning concrete, brick, or stone. Good balance of power and safety.
• 25° nozzle: The most common for house exteriors. It’s wide enough to cover more area, gentle enough to avoid damage. This is what you’ll see most often on a pro’s wand.
• 40° nozzle: For rinsing soap or cleaning delicate surfaces like vinyl siding or aluminum. Used after the main cleaning to rinse without stripping.
• Rotating turbo nozzle: A high-end tool that spins the water stream in a circular pattern. It cuts cleaning time by up to 50% on tough algae or moss-covered surfaces without increasing pressure.

Professionals carry at least three nozzles on every job. They switch based on the surface, the dirt type, and the weather. A cold, damp morning might need a wider spray to avoid freezing water on the surface.

Hot Water vs. Cold Water

Most homeowners think pressure washing means cold water. But pros often use hot water machines-especially for homes with heavy grease, oil, or biological buildup like mold and algae.

Hot water (up to 200°F) breaks down organic matter faster. It’s not just about heat-it’s about chemistry. Warm water helps cleaning solutions penetrate deeper and work more effectively. A cold water machine might take 45 minutes to clean a moldy wall. A hot water unit can do it in 15.

Hot water pressure washers cost more-£4,000 to £7,000-but they’re worth it for businesses. In the UK, where damp conditions breed mold year-round, hot water isn’t a luxury. It’s standard for any serious house cleaning service.

Chemicals and Cleaning Solutions

Pressure washing isn’t just water. It’s water + chemistry. Professionals use specialized cleaners designed for specific surfaces and contaminants.

• Sodium hypochlorite (bleach-based): Used for killing mold, mildew, and algae. Typically diluted 1:10 with water. Applied with a low-pressure sprayer before the main wash.
• Oxygen bleach: A safer alternative for homes with plants, pets, or nearby water sources. Doesn’t harm vegetation or corrode metal. Works slower but is gentler on wood and painted surfaces.
• Biodegradable degreasers: For homes with oil stains from gutters, driveways, or garage floors.
• Concrete cleaners: Formulated to lift rust, tire marks, and grease without etching the surface.

Pros never use household bleach straight from the bottle. It’s too strong, damages surfaces, and kills nearby plants. They also avoid cheap, big-box store cleaners-many contain fillers that clog nozzles or leave residue.

Most professionals mix their own solutions based on the job. They carry 3-5 different concentrates in labeled containers and test a small area first. A house with moss on the roof? Different mix than one with dirt-caked brick.

Surface-Specific Techniques

Not all houses are the same. A 1930s brick cottage in Brighton needs different handling than a 2010s vinyl-sided suburban home.

• Brick and stone: Use 25° nozzle at 2,500-3,000 PSI. Keep the wand 12-18 inches away. Work from top to bottom to avoid streaking.
• Vinyl siding: Use 40° nozzle at 1,500-2,000 PSI. Never spray upward-water can get behind panels and cause rot. Always spray diagonally downward.
• Wood siding or decks: Use 40° nozzle at 1,000-1,500 PSI. Too much pressure digs into grain. Many pros use a wood cleaner first, then rinse gently.
• Roof shingles: Most pros avoid pressure washing roofs entirely. Instead, they use low-pressure sprayers with oxygen bleach or soft washing systems. High pressure can lift shingles and void warranties.
• Windows and gutters: These are cleaned separately with squeegees and soft brushes. Pressure washing near windows risks water intrusion.

One mistake many DIYers make? Cleaning the whole house at once. Pros work in sections. They apply cleaner, let it sit 5-10 minutes, then rinse. This gives the solution time to break down grime. Rushing leads to streaks and missed spots.

What They Don’t Use

There’s a lot pros avoid:

• Electric pressure washers under 2,000 PSI: Too weak for full-house jobs. They’re for patios and garden furniture.
• Pressure washers without variable pressure control: You can’t adjust pressure on the fly. That’s dangerous on mixed surfaces.
• Homemade cleaners (vinegar, dish soap, bleach): Vinegar corrodes metal parts. Dish soap creates too much foam and clogs systems. Bleach damages seals and finishes.
• Using a pressure washer on glass, plastic, or painted metal without protection: These surfaces can crack, melt, or peel instantly.

Some DIYers think more pressure = better results. But pros know better. It’s not about power-it’s about precision. A professional’s skill lies in knowing when to back off, when to switch nozzles, and when to walk away from a surface entirely.

Why DIY Pressure Washing Often Goes Wrong

People rent machines from Home Depot or B&Q thinking they’ll save money. But here’s what usually happens:

• They use the wrong nozzle and strip paint off the garage door.
• They spray upward and water seeps behind siding, causing rot.
• They use bleach and kill their garden.
• They run out of time and leave streaks.
• They damage gutters, window seals, or roof tiles.

Repairs cost more than hiring a pro. A single damaged vinyl panel costs £150 to replace. A water-damaged wall behind siding? That’s £1,000+.

Professionals carry insurance. They know how to protect plants, windows, and doors. They have the right gear to avoid injury and damage. It’s not just about the machine-it’s about experience.

What to Look for When Hiring a Pro

If you’re hiring someone, ask:

• Do you use hot water or cold water machines?
• What PSI and GPM do your machines run at?
• What cleaning solutions do you use? Can I see the labels?
• Do you cover plants and windows?
• Do you have insurance?

Any reputable pro will answer these without hesitation. If they say, “I just use the machine,” walk away. Pressure washing is a trade. It’s not magic.

In Brighton, where sea salt, damp, and moss are constant problems, pros know the local conditions. They adjust their methods for coastal homes, listed buildings, and narrow streets. A one-size-fits-all approach doesn’t work here.

Final Thoughts

Pressure washing a house isn’t about brute force. It’s about matching the right tool to the right surface, at the right pressure, with the right chemical. Professionals don’t just spray water-they solve problems. They protect your home while making it look new again.

If you’re thinking of doing it yourself, understand the risks. If you’re hiring someone, don’t just pick the cheapest. Look for someone who knows the difference between a 25° and a 40° nozzle-and why it matters.