What’s the Best Size Pressure Washer for House Washing? A Pro’s Guide to GPM
So, you’re ready to start cleaning houses, whether it’s your own or for your new business. You walk into a store or browse online and get hit with a wall of numbers: PSI, GPM, HP, CC… it’s a lot. What’s the most important factor for washing a house effectively and efficiently?
While many people get fixated on PSI (Pounds per Square Inch), the real secret to cleaning speed is GPM (Gallons Per Minute).
For most house washing, you’ll be using a technique called soft washing. This involves using special spray tips with a larger orifice that lowers the output pressure to under 200 PSI. This gentle pressure is safe for siding, paint, and windows. You’ll combine this with a downstream chemical injector, which pulls a cleaning solution (like sodium hypochlorite and a surfactant) and mixes it with the water flow from your machine. The higher your GPM, the more water dilutes your cleaner, but the faster you can rinse.
Let’s break down the three best GPM options to help you choose the perfect machine for your needs.
The 4 GPM Machine: The Perfect Starter 👍
A 4 GPM pressure washer is the ideal entry point for a serious DIY homeowner or a new contractor on a budget.
Benefits: Its biggest advantage is convenience. Most homes have enough water flow from a standard spigot to run a 4 GPM machine without issue, meaning you likely won’t need a buffer tank. (It’s always smart to test the flow rate first, especially on a well system!). When downstreaming, your cleaning solution is mixed with less water, resulting in a stronger chemical mix. This can be a big help for melting away tough algae and grime.
Drawbacks: The lower flow means rinsing will take longer. Cleaning concrete with a surface cleaner will also be a slower process, as you’ll be limited to a smaller-sized attachment (around 16 inches) to match the machine’s output.
Verdict: This is a fantastic, capable machine. It will get the job done right, it just takes a bit more time than the bigger units. Perfect for someone who doesn’t need to wash multiple houses in a single day.
The 5 GPM Machine: The Versatile Workhorse 💪
This is the “best of both worlds” option. A 5 GPM machine offers a significant jump in speed and performance over its smaller sibling.
Benefits: That one-gallon difference in GPM makes a real difference in rinsing speed and overall job time. It still produces a strong cleaning solution when downstreaming, making it a great choice for tough, porous surfaces like brick, stucco, and Dryvit that are heavy with organic growth.
Drawbacks: At this size, a buffer tank is highly recommended. A buffer tank is a reservoir (typically 50-100 gallons) that is fed by the home’s spigot. Your pressure washer then pulls water from the tank, ensuring the pump is never “starved” for water, which can cause costly damage. This requires a more complex setup, usually on a trailer.
Verdict: A stellar choice for a contractor washing a couple of smaller houses a day or someone who wants pro-level results and can accommodate a buffer tank.
The 8 GPM Machine: The Professional’s Choice 🚀
If speed is the name of the game, an 8 GPM pressure washer is the undisputed champion for residential washing.
Benefits: The performance leap is massive. Rinsing is incredibly fast, which can shave hours off a large job. You can efficiently run large surface cleaners (20 inches or more), making concrete cleaning much quicker. The high flow is also excellent for thoroughly rinsing landscaping to dilute any chemical runoff and protect plants.
Drawbacks: A buffer tank is not optional, it’s a requirement. You have to keep a close eye on your water level, as an 8 GPM machine can drain a tank quickly if the home’s water supply is slow. The biggest trade-off is the cleaning solution strength. Because the chemical is diluted by 8 gallons of water per minute, the final mix is weaker than the other machines. It’s still perfect for standard vinyl or painted Hardie board, but it can struggle with deeply embedded algae on porous surfaces, sometimes requiring multiple applications.
Verdict: For a professional contractor focused on maximizing daily output, this is the machine to own.
How We Use Both on Our Professional Rig
On our professional house washing trailer, we have both a 5 GPM and an 8 GPM machine, and we use them for different tasks.
The 8 GPM is our daily driver. We use it on almost every residential job. The speed it provides for washing and especially for rinsing is unmatched, allowing us to complete large homes and their flatwork efficiently. Time is money, and this machine saves a lot of it.
However, when we run into a brick or stucco home that hasn’t been cleaned in a decade, that’s when the 5 GPM shines. The stronger chemical solution it produces is perfect for breaking down the stubborn, deep-set organic growth on these porous surfaces. We also prefer the 5 GPM for delicate work like wood decks and fences. Its slightly lower flow is easier to control, allowing us to clean the wood effectively with under 1000 PSI without causing damage.
Ultimately, the best pressure washer depends on your goals, budget, and the scale of your work. Choose wisely, and you’ll have the right tool to deliver amazing results. Happy washing!
Nick LoomisOwner-Operator
Since 2012, Nick Loomis of Hot Water Pressure Washing has been a trusted expert in Tallahassee's exterior cleaning industry. With over a decade of experience, he's passionate about two things: delivering incredible results for his customers and finding innovative solutions to do the job right.
