We often talk about the benefits of a 3 in. vs 4 in. downspout pipe for specific buried downspout applications. However, you may still wonder how much of a difference the downspout pipes can make until you see it yourself.

Let’s take you through our little backyard demonstration. We’re going to run water through a 4 in. downspout, and then we’re going to reduce that to a 3 in. I think you’re going to be really shocked when you see the results we get.

Difference in Water Pressure Between 3 in. vs 4 in. Downspout Pipe

We’re mocking three by four downspouts that run 50 feet long. These are the bigger of the two sizes we have in the United States. You can see that we’re pumping water through both the 4 in. clear corrugated pipe and the 3 in. clear corrugated pipe. We’re running 140 gallons per minute through each system.

3 in vs 4 in Downspout Pipe

When the water hits the 3 in. what do you expect to happen? Do you expect it to fall behind? At what point does the 3 in. become overwhelmed? We have them on the same slope. We have everything set up identical to provide an excellent, accurate demonstration.

Flow of Water Comparison

You can see the 3 in. pipe on the right is moving water. The water is agitating and moving quickly at a good velocity. On the left, we have the 4 in. line. You see a difference in agitation. It’s not flowing as fast as the water in the 3 in. pipe you see here. So right away, we see that there’s a velocity difference.

Difference Between Downspout Pipes with Increased Water Pressure

To make this more interesting, we ran 280 gallons through the 4 in. to get the water pressure that we were looking for. We were happy with our previous results, but what’ll happen when we run 280 gallons through the 3 in.?

280 Gallons Test

Well, there you have it. White water gushing from that popup emitter. The velocity and the water pressure has increased again. Look at that flow of water. This is 280 gallons per minute. More than likely, the 3 in. line is going to outperform the 4 in. line when you put it up against lower flow and moderate flow. Will the 3 in. pipe eventually get overwhelmed, is the question. Are there other liabilities that come with the 3 in. pipe? We have to weigh out the differences.

3 in vs 4 in: Which Should You Use in Your Application?

Before I tell you where you want to use the 3 in. downspout pipe, I have to talk about the 4 in. pipe, which is industry standard. You have to realize that the 4 in. pipe is going to do everything for you. The 4 in. line is a one size fits all. It’s great for tying multiple downspouts into your main.

The 3 in. pipe, however, does have its limitations. And I’m going to share those with you.

You could run up to 2 downspouts on the same 3 in. line. If you go to 3 downspouts, you need to bump it up to a 4 in. main. It’s only going to move so much water. At some point, the velocity is not going to continue to increase and pick up. You’re going to overwhelm it, and you’re going to end up having to fall into the 4 in. pipe category.

Which Should You Use in Your Application

I can share with you that homeowners do not clean their distribution boxes and their inline catch basins. They let them build up until they can’t hold any more shingle gravel, tree seeds, and decomposed leaves. Debris soon ends up pouring into the pipe itself. When you have a 4 in. line, it displaces so much more area; that’s where the 4 in. pipe comes in. It rescues the homeowner and saves them from themselves.

The 3 in. downspout pipe shines when 2 lines are tied to a pop-up emitter V2.0. The velocity of water on two lines remains high. Our pop-up emitter was designed for homeowners to fit their hands in and clean the basin, making it a low-maintenance option.

Providing the Best Materials for Your Downspout Needs

French Drain Man provides tips for DIYers, as well as professional installations for all your drainage needs. With over 35 years of experience, we’re the experts in drainage-related. We use the best, purpose-built materials to provide powerful drainage solutions that can last a lifetime.

If you want it done right the first time, call French Drain Man at 248-505-3065!