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Before installing a new HVAC system, a technician will usually perform something called a backflow test. Backflow is generally more of a plumbing concern, but it’s also HVAC adjacent since the pipes required for some furnaces, air conditioners, and other HVAC devices are also at risk for backflow. A test is a good way to make sure that nothing from your HVAC pipes is going to contaminate the rest of your plumbing, and vice-versa. Here’s a little information on how backflow tests work, why they’re so important, and how you can perform one yourself if you like.


HVAC 101 Everything you need to know


What is a Backflow Test and How Does It Work?

Typically, every pipe in your plumbing system flows in only one direction. Clean water flows into your plumbing from the water main, comes out through your sink, shower, or any other appliance, and then goes down the drain once it’s been used so it can flow back out. However, sometimes certain pressure imbalances or suction can cause the water to start flowing backward. When backflow occurs, dirty water from your shower drain, dishwasher, or even sewage water can find its way into your supply of clean drinking water. Not only is this extremely unpleasant, but it can also lead to water damage in your home or illness if you unknowingly drink the backflow water.


In order to avoid this problem, modern homes are outfitted with devices called backflow preventers. As you can probably guess from the name, backflow preventers are designed to stop backflow before it reaches the rest of your water supply. This happens through special valves, vacuum suction, and sometimes air gaps. If your backflow preventer is working properly, you might not ever even know it was there. However, if the preventer fails, you could find yourself with sewage water coming out of your kitchen sink, and nobody wants that.


With all that in mind, you might still be wondering “What is a backflow test?” When a plumber or HVAC technician performs a backflow test, they’re checking each of the backflow preventers in your house to make sure they’re all working properly. There’s typically a backflow preventer installed in the cross-connections between your main water supply and each appliance that pulls from it. Backflow testing involves going to those connections and making sure every preventer is working the way it should. Even a single broken backflow preventer can contaminate your clean water plumbing, so it’s important to be thorough.


In addition to the backflow testing, a technician or plumber might also conduct a water pressure test. Pressure imbalances are the cause of almost all backflow issues, so it’s important to check the pressure throughout your house to make sure there are no trouble spots. A sudden drop in water pressure can cause dirty water to be sucked back into the clean water supply – this is called back-siphonage, and it’s the most common cause of backflow. It’s essentially the same as sucking water through a straw; the lowered air pressure in your mouth causes water to rise through the straw due to atmospheric pressure. On the other side of things, if the water pressure is too high in any part of your plumbing, it can cause something called back-pressure. This is like blowing through a straw and pushing the water back into the glass; the higher pressure in your mouth forces the air and water out the other end of the straw. Either of these pressure imbalances will cause backflow to enter your clean water supply, so regular water pressure tests are a good way to stay ahead of any potential issues.


What are the Advantages of a Backflow Test?

The most main benefits of backflow testing should be pretty apparent. Nobody wants wastewater in their drinking supply, and making sure the backflow prevention systems are functioning properly is the best way to keep that from happening. Backflow can also cause serious damage to your plumbing or the areas surrounding your fixtures if flooding also occurs. If you’re wondering how to prevent backflow, regular maintenance is the best practice for avoiding any number of potential issues down the road. It’s a lot better to shell out about $80 once a year instead of potentially thousands of dollars to fix your plumbing after backflow has occurred.


Backflow can also cause serious illnesses in you or your family if you drink the tainted water inadvertently. The main culprit for backflow-related illness is sewage water. Besides the obvious reasons why nobody should want to drink water contaminated by sewage, human waste also contains a pretty wide variety of bacteria, viruses, and parasites that can wreak havoc on your body. Many diseases like typhoid fever, dysentery, and giardia have nearly disappeared from everyday American life because of modern-day water treatment and hygiene techniques, but backflow can hit you with any of these blasts from the past.


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The most common single cause of backflow is your everyday garden hose, and this kind of contamination can come with adverse health effects as well. When water from your lawn or garden backs up through the hose into your clean supply, it brings everything that was in the dirt with it. This can include parasites and bacteria as well as any fertilizer or pesticide that you use on your lawn. Ingesting water that’s been tainted with fertilizer can lead to nitrate poisoning, which requires immediate medical attention and can cause hospitalization and long-term health effects. Other potential sources of waterborne illness include standing water from sprinkler systems or boilers and industrial chemicals if you’re in a commercial building.


If your backflow preventers fail, the effects might not be limited to just your home. If backflow is allowed to reach and contaminate the water main, you could end up with a full-blown public health crisis in your neighborhood. For this reason, regular backflow testing is legally required by many states, including California. A failure to stay up to date on backflow testing could result in some fines or penalties, especially if you’re running a business. Luckily, all these consequences can be avoided if you stay on top of your maintenance schedule and give your plumber or HVAC technician a call every year. The testing is relatively inexpensive, and you can include it as part of your regular HVAC maintenance.


How to Perform and Interpret Results from a Backflow Test

While the simplest option is to just have a professional take care of your backflow testing, hardcore do-it-yourselfers might prefer to handle the testing themselves. In order to test your own backflow preventers, all you need is a backflow testing kit and some rudimentary plumbing skills. The cost of a testing kit can range from about $200 all the way up to $2000, so be prepared to spend if you want to test everything yourself.


Step 1 – Shut off Water

First things first, you should shut off the water supply in your house. Make sure to warn everyone in your household before you start the testing process since they won’t be able to use the water until you’re finished.


Step 2 – Check Device

There are several different types of backflow preventers, and each one has its own unique testing process. Any manual you find will list the different procedures for each type of preventer, so all you have to do is identify which kind you have. You can find this out by checking the documentation provided by the manufacturer when you purchased the preventer.


Step 3 – Gather Test-Cocks

A test-cock, often colloquially referred to as a “thingy,” is a small valve that you can attach to another valve for testing purposes. The test-cock draws a little water from the full valve so you can test the pressure without having to take the whole system apart. You will generally need at least two test-cocks for backflow testing, but the exact number will depend on the type of preventer you have. You should make sure to label each test-cock with a number so you can keep track of which is which.


Step 4 – Close Downstream Valve

Any backflow preventer should have two different shut-off valves: one upstream (closer to the source of the water) and one downstream (closer to the water’s destination). In order to test the preventer, you’ll have to shut the downstream valve while leaving the upstream one open. This allows the preventer to fill with water but blocks any flow further than that. Don’t forget to open the valve again when you’re finished!


Step 5 – Attach Hoses and Test

The specifics of this step can vary pretty wildly depending on the type of preventer you’re testing. There are about 10 different procedures, one for each type, so you’ll have to find the directions for yours in the documentation that came with the testing kit. The directions will also explain how to read the results from the backflow test, which involves checking a few different gauges for pressure readings.


Once you’ve finished these steps and noted all the readings, don’t forget to replace everything and open the downstream valve again. While the procedures involved in testing backflow preventers might seem complicated when you first give them a try, there’s no reason why you shouldn’t be able to take care of them yourself. That said, having them handled professionally is relatively inexpensive, so that’s an excellent choice as well.


What Does it Mean if There’s No Water Flow? – If there’s no water at all flowing into the preventer, double-check to make sure you closed off the right shut-off valve. If the upstream valve is open and you’re still not getting any water flowing from the source, then there could be a problem with the preventer or even the water main itself, and you should get in touch with a plumber to take a look.


Why You Should Perform Regularly Scheduled Water Pressure Tests

Aside from the regular backflow testing, it’s always a good idea to check the water pressure fairly regularly as well. This is a lot easier to do and only requires you to attach a gauge to a water fixture in your house. Home water pressure is usually handled by a single regulator somewhere in your home, so you should only need to test a single fixture. If you get your water from a municipal source like a water main, test the pressure at an outdoor spigot close to the road. If you use a well, use a faucet or fixture that’s close to the pressure tank attached to the well.


Because imbalances in water pressure are what cause backflow, catching any potential high or low-pressure spots in your plumbing before they become serious problems is ideal. If you’d prefer not to handle this on your own, you can always get your regular plumber to check the water pressure when they test the backflow prevention. We recommend checking the water pressure about once a year or more, depending on the specifics of your situation.


Modern plumbing works through pressure almost exclusively. This is an extremely efficient way of moving water from one place to another, but it also means any sudden drop or spike in pressure can wreak havoc on the system. Besides causing backflow, pressure issues can also lead to burst pipes and leaks as well as rendering fixtures ineffective. If you notice a change in the water pressure of any of your fixtures, like the shower or the sink, you should have the pipes checked by a professional. You could be at risk of backflow, pipe damages, flooding, or other costly plumbing emergencies.


If you need to schedule a backflow testing appointment, or you have any questions about HVAC systems, feel free to get in touch with us at Valley Comfort Heating & Air through our website here, over the phone at (707) 329-4120, or visit one of our locations in Sonoma or Napa Valley. We’ve been handling HVAC repair, installation, and maintenance in the Bay Area for years, and we have the experience and superior customer service you’re looking for in a service company.


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