How to Blow out Sprinkler Lines? DIY Winterization Guide

Introduction

Frozen temperatures can cause catastrophic damage to your irrigation system in a matter of hours, leading to burst pipes, broken sprinkler heads, and ruined control valves that can cost thousands of dollars to repair. For homeowners in cold climates, learning how to blow out sprinkler lines is one of the most important fall maintenance tasks you can complete to protect your landscaping investment. This DIY winterization process is far more affordable than hiring a professional, and it only takes 1 to 2 hours for most residential systems. In this comprehensive guide, we’ll walk you through every step of how to blow out sprinkler lines safely and effectively, including the tools you’ll need, step-by-step instructions, common mistakes to avoid, and when it’s better to call in a pro. By the end of this guide, you’ll have all the information you need to winterize your system yourself and avoid costly freeze damage come spring.

• Introduction
• Why Winterize Your Sprinkler System?
• What You’ll Need to Blow Out Sprinkler Lines
• Step-by-Step Guide to Blowing Out Sprinkler Lines
• Air Compressor Types: Which Is Best for the Job?
• Common Mistakes to Avoid When Blowing Out Sprinkler Lines
• Pro Tips for a Successful Winterization
• When to Hire a Professional Instead of DIY
• Frequently Asked Questions
• Conclusion

Why Winterize Your Sprinkler System?

Many homeowners assume that their sprinkler system is built to withstand cold temperatures, but this is a dangerous misconception. Even systems designed for cold climates can suffer damage if water is left trapped in pipes during a hard freeze. When water freezes, it expands by approximately 9% in volume. Even a small amount of water left in your sprinkler pipes can generate enough pressure to crack PVC piping, split copper fittings, and break plastic sprinkler heads. The damage often goes unnoticed until spring, when you turn on your system to find geysers spraying from broken pipes or dead spots in your lawn from non-functioning heads. According to irrigation industry data, the average cost to repair freeze-damaged sprinkler systems ranges from $2,000 to $5,000, depending on the extent of the damage and the size of your property. Repairs may include replacing entire sections of pipe, fixing broken valves, and replacing dozens of sprinkler heads, not to mention the cost of repairing any landscaping damage caused by flooding from broken pipes. In contrast, DIY winterization costs as little as $50 if you already own an air compressor, or $100 to $150 if you rent one from a local home improvement store. Even hiring a professional to winterize your system typically costs between $100 and $200, a tiny fraction of the cost of repairs. For most homeowners, learning how to blow out sprinkler lines is a no-brainer when it comes to protecting their property and budget.

What You’ll Need to Blow Out Sprinkler Lines

Before you start the winterization process, gather all the necessary tools and materials to avoid interruptions. Having everything on hand will make the process faster and safer. Here’s what you’ll need:

• Air compressor with a minimum of 10 CFM (cubic feet per minute) and adjustable pressure up to 100 PSI. CFM measures the volume of air the compressor can deliver; higher CFM means you can clear zones faster and more effectively. For most residential systems, a 10-20 CFM compressor is ideal.
• Air pressure regulator and control valve. This attaches to the compressor outlet and lets you set a consistent PSI to avoid over-pressurizing your system. Never use a compressor without a regulator, as even small compressors can deliver PSI high enough to burst pipes.
• Hose adapter that fits the blowout port on your sprinkler system’s backflow preventer. Most residential backflow preventers use a 3/4-inch or 1-inch threaded blowout port, so check your system’s fittings before renting or buying an adapter.
• Safety glasses and work gloves. Air compressors can blow debris out of pipes, and high-pressure air can cause injury if it escapes from a loose connection.
• Adjustable wrench or pliers to tighten connections.
• Optional: Frost blanket or insulation wrap for above-ground backflow preventers and valves, to add extra protection after blowout.

Note: If you don’t own an air compressor, you can rent one from a home improvement store, equipment rental shop, or some hardware stores for $25 to $100 per day, depending on the size and type. Be sure to reserve your equipment in advance in the fall, as rental shops often run out of compressors during peak winterization season.

Step-by-Step Guide to Blowing Out Sprinkler Lines

The actual process of blowing out your sprinkler lines is straightforward, but it requires attention to detail to avoid damaging your system. Follow these steps in order for the best results.

Pre-Winter Preparation

Proper preparation is the key to a successful sprinkler line blowout. Skipping steps here can lead to leftover water in your pipes or damage to your system. Follow these steps to get ready:

1. Monitor the weather forecast to ensure no hard freezes (temperatures below 28°F / -2°C for more than 4 hours) are expected for at least 24 hours after you complete the winterization process. If a freeze is forecast shortly after you plan to winterize, wait until the cold snap passes to avoid refreezing any leftover water.
2. Locate your sprinkler system’s main water shutoff valve. This is usually located near your home’s main water meter, or attached to the backflow preventer assembly outside. Turn the valve completely to the off position to stop water from flowing into the sprinkler system. This is a critical step – if you leave the main water on, air pressure will push water back into your home’s supply line, or water will continue to enter the sprinkler pipes while you blow them out, leaving excess water behind.
3. Locate the system drain valve, if your sprinkler system has one. This is usually at the lowest point of your irrigation pipe layout. Open the valve and let all standing water drain out of the pipes naturally. This step reduces the amount of water you need to blow out with the air compressor, making the process faster and more effective.
4. Remove any above-ground sprinkler heads that are low to the ground, or cover them with a thick cloth or towel to protect them from damage caused by high-pressure air. While rare, air pressure can blow the cap off a sprinkler head if it’s loose.
5. Locate your sprinkler controller (the timer box that controls your zones) and set it to manual mode. This will let you activate each zone individually without relying on the scheduled watering times. Label each zone if your controller isn’t already marked, so you don’t miss any sections of your system.

Setting Up Your Air Compressor

Correctly setting up your air compressor is critical to avoid damaging your sprinkler system or the compressor itself. Follow these steps carefully:

1. Attach the air hose to the compressor’s outlet, then attach the blowout adapter to the end of the hose. Make sure all connections are tightened securely with an adjustable wrench or pliers to prevent air leaks. Loose connections can cause the adapter to blow off while the compressor is running, leading to injury or damage.
2. Set the compressor’s pressure regulator to 80 PSI maximum. Even if your compressor can deliver higher PSI, never exceed 80 PSI for residential sprinkler systems. Most residential irrigation pipes are made of PVC or polyethylene, which can burst at pressures above 100 PSI, and even 80 PSI is more than enough to clear all water from the lines. Higher pressure will not clear the lines faster, and it will only increase the risk of damage.
3. Turn on the compressor and let it build up full pressure in the air tank. Most compressors have a pressure gauge that shows when the tank is full. Do not start the blowout process until the tank is fully pressurized, as inconsistent air pressure will leave water trapped in the pipes.

Blowing Out Each Sprinkler Zone

This is the core of the winterization process. Take your time with each zone to ensure all water is cleared:

1. Start with the first zone: Open the corresponding valve on the backflow preventer, or activate the zone manually via your sprinkler controller. You should hear water flowing through the pipes to the sprinkler heads.
2. Hold the air hose adapter firmly against the blowout port on the backflow preventer. Make sure the connection is tight to prevent air from escaping.
3. Slowly activate the air compressor to release air into the zone. Do not open the compressor valve all the way at once – a slow, steady flow of air is more effective and less likely to damage the system.
4. Monitor the sprinkler heads in the active zone. At first, you will see water spraying out of the heads, followed by a mix of water and air, then just mist, and finally only air. Once all visible water has been cleared from the heads and you only see air blowing out, turn off the compressor immediately for that zone. Do not leave the compressor running on an empty zone, as the friction from air moving through empty pipes can generate enough heat to melt plastic valves and fittings, or damage the compressor motor.
5. Close the zone valve on the backflow preventer, then move to the next zone. Repeat this process for every zone in your system. Most residential systems have 4 to 8 zones, so the blowout process will take 30 minutes to an hour total.

Important note: Never skip zones, even if they are rarely used. Water can still be trapped in pipes for unused zones, and frozen water can cause damage that affects the entire system.

Final System Checks

Once you’ve blown out all zones, complete these final steps to ensure your system is fully protected:

1. Turn off the compressor and release any remaining air pressure from the hose by pressing the pressure release valve on the compressor or hose.
2. Close the main sprinkler shutoff valve if you haven’t already, to prevent any accidental water flow into the system over the winter.
3. Open the system drain valve again to let any remaining water that was pushed to the low point of the system drain out completely.
4. Wrap the above-ground backflow preventer, control valves, and any exposed pipes in insulation wrap or a frost blanket. Secure the wrap with duct tape or zip ties to keep it in place. This extra layer of protection prevents these components from freezing even if temperatures drop unexpectedly.
5. Store your air compressor and tools in a dry, protected area. Drain any water from the compressor’s air tank to prevent rust and damage during storage.

Air Compressor Types: Which Is Best for the Job?

Not all air compressors are suitable for blowing out sprinkler lines. Using the wrong type can leave water trapped in your pipes, or damage your system. The two most important specs to look for are CFM (air volume) and PSI (air pressure). Below is a comparison of the most common compressor types used for sprinkler winterization:

For most residential systems, a 10-20 CFM electric or gas-powered wheelbarrow compressor is the best choice. Electric compressors are quieter and require no fuel, but they need access to a power outlet. Gas-powered compressors are more portable and work in areas without power, but they are louder and require gasoline to run. Avoid small pancake compressors with less than 5 CFM, as they do not deliver enough air volume to clear all water from your pipes, especially for systems with long pipe runs or multiple zones. If you’re unsure what size compressor you need, ask the staff at the rental shop – they can recommend the right size based on your system’s size and number of zones.

Common Mistakes to Avoid When Blowing Out Sprinkler Lines

Even experienced DIYers can make mistakes when blowing out sprinkler lines, leading to leftover water or system damage. Avoid these common errors to ensure a successful winterization:

• Over-pressurizing the system: As mentioned earlier, never exceed 80 PSI for residential systems. Over-pressurizing can burst PVC pipes, crack fittings, and blow the caps off sprinkler heads. Always use a pressure regulator to keep PSI consistent.
• Using a low-CFM compressor: A compressor with less than 5 CFM will not generate enough air flow to push water out of long pipe runs or multiple zones. This leaves water trapped in the pipes, which will freeze and cause damage. If you have a system with more than 6 zones, rent a compressor with at least 10 CFM.
• Running the compressor on an empty zone: Once all water is cleared from a zone, turn off the compressor immediately. Running air through empty pipes creates friction heat that can melt plastic valves, damage the compressor motor, and even cause a fire in extreme cases.
• Forgetting to turn off the main water supply: If the main water is left on, water will continue to enter the system while you blow it out, leading to excess water left in the pipes. Always turn off the main shutoff valve before starting the blowout process.
• Skipping the pre-drain step: Draining standing water first reduces the amount of water you need to blow out, making the process faster and more effective. Skipping this step will make the blowout take longer and increase the risk of leftover water.
• Not insulating above-ground components: Even after a successful blowout, above-ground backflow preventers, valves, and pipes can freeze if temperatures drop well below freezing. Wrapping these components in insulation or a frost blanket adds an extra layer of protection.

Pro Tips for a Successful Winterization

Follow these expert tips to make your sprinkler line blowout faster, easier, and more effective:

• Winterize your system 1 to 2 weeks before the first expected hard freeze. This gives you a buffer in case the freeze comes earlier than forecast, and avoids waiting until the last minute when rental equipment may be in high demand.
• If your system has an automatic drain feature, activate it 24 hours before blowing out the lines to let as much water as possible drain naturally.
• Mark each zone in your controller before starting, so you don’t miss any sections of your system. Unused zones are just as likely to freeze as frequently used ones.
• Work with a helper: one person can hold the air hose adapter steady, while the other activates the compressor and monitors the sprinkler heads to make sure all water is cleared.
• After winterization, set your sprinkler controller to “rain” or “off” mode for the winter. This prevents the system from accidentally turning on during a warm spell, which can push water into frozen pipes and cause damage.
• In areas with extremely cold winters (below 0°F / -18°C), add a layer of mulch or straw around exposed pipes and valves for extra insulation.
• Keep a record of the date you winterized your system, so you don’t forget in future years. Set a reminder on your phone or calendar for the same time each year.

When to Hire a Professional Instead of DIY

While blowing out sprinkler lines is a straightforward DIY task for most homeowners, there are some situations where it’s better to hire a professional:

• You have a very large system (more than 15 zones) that requires a high-volume commercial compressor that is difficult to rent or operate.
• Your system has complex components like booster pumps, high-pressure irrigation zones, or specialized equipment that can be damaged by incorrect air pressure.
• You are not comfortable working with air compressors or do not have experience with basic plumbing tasks.
• You have physical limitations that make it difficult to lift or move a heavy air compressor.
• You live in an area with extremely cold temperatures and want extra assurance that your system is fully protected from freeze damage.

Professional sprinkler winterization typically costs between $100 and $300, depending on the size of your system and your location. While this is more expensive than DIY, it’s still a small cost compared to the $2,000+ you could spend repairing freeze damage. If you’re unsure about winterizing your system yourself, hiring a professional is a worthwhile investment for peace of mind.

Frequently Asked Questions

General Winterization Questions

How often do I need to blow out my sprinkler lines?

You only need to blow out your sprinkler lines once per year, before the first hard freeze of the winter. If you forget one year and your system freezes, you’ll need to repair any damage before winterizing the following year. In mild climates where temperatures rarely drop below freezing, you may not need to winterize at all, but it’s still a good idea to drain the system if a hard freeze is forecast.

Can I use a garden hose to blow out my sprinkler lines?

No, garden hoses only have 40-60 PSI of water pressure, which is not enough to push all the water out of your sprinkler pipes. You need an air compressor that can deliver steady, high-volume air at 80 PSI to clear all standing water from the system. Using a garden hose will leave water trapped in pipes, which will freeze and cause damage.

What CFM compressor do I need for my sprinkler system?

As a general rule, you need a compressor that delivers at least 5 CFM per zone. For example, a 6-zone system needs a minimum of 30 CFM, but a 10-20 CFM compressor is sufficient for most residential systems. Larger commercial systems may require 20+ CFM. If you’re unsure, rent a higher CFM compressor than you think you need – it’s better to have too much air flow than too little.

What happens if I forget to blow out my sprinkler lines?

If water is left in your sprinkler pipes and temperatures drop below freezing, the water will expand as it freezes, cracking PVC pipes, breaking sprinkler heads, and damaging control valves. Repairs can cost anywhere from $1,000 to $5,000 depending on the extent of the damage. If you forget to winterize and a freeze is forecast, you can try to drain the system manually by opening all drain valves and sprinkler heads, but this is not as effective as blowing out the lines with an air compressor.

Can I winterize my sprinkler system myself?

Yes, most homeowners can winterize their sprinkler system themselves with a rented air compressor and basic tools. The process takes 1-2 hours for most residential systems. As long as you follow the steps in this guide, avoid common mistakes, and use the correct pressure settings, DIY winterization is a safe and cost-effective option. If you have a complex system or are uncomfortable working with air compressors, hiring a professional is a good alternative.

Conclusion

Learning how to blow out sprinkler lines is one of the simplest and most cost-effective ways to protect your sprinkler system from costly freeze damage. By following the step-by-step guide in this article, using the right tools, and avoiding common mistakes, you can winterize your system in just a few hours each fall. Remember to always use a pressure regulator to keep PSI below 80, choose a compressor with enough CFM for your system size, and insulate all above-ground components for extra protection. If you have a large or complex system, or are uncomfortable working with air compressors, hiring a professional is a reliable alternative. Taking the time to winterize your sprinkler system each year will save you thousands of dollars in repairs, and ensure your lawn is ready to thrive as soon as spring arrives.