A Vacuum Relief Valve installed at the highest point in this solar pool heating system relieves negative air pressure from water draining from the panels.

Vacuum Relief Valve for Solar Pool Heaters

In Education 64 Comments

What is a vacuum relief valve, and why is it required in a solar pool heating system?



A valve must be installed in every solar pool heating system to allow air into the system when pool water drains out of the panels. This relieves the vacuum that would be created by falling water inside the solar panels and plumbing on the roof. There are various styles of vacuum relief valves, but all automatically allow air into the system when there is a vacuum created by a void of water pressure. We in the industry refer to a vacuum relief valve as a VRV.

Properly installed systems are designed to drain back to the pool every night when the pool pump shuts off. The main purposes of this is to eliminate the risk of freeze damage in the panels and plumbing. Freezing water expands and can bursts panels and pipes, and solar panels have a high ability to emit heat to the night sky, making them susceptible to freezing, even here in Southwest Florida at times. Another reasons panels should drain is to reduce the risk of stagnation in the summer, causing overheating and warped and discolored plumbing. Finally, draining panels for service purposes is helpful.

Some panels cannot drain automatically because of the way they are plumbed (either purposely or because the installer doesn’t know what they are doing). Systems that do not drain naturally with gravity should have a manually operable drain valve installed. In this case, a vacuum relief valve is still required.

A vacuum relief valve is required in every solar pool heating system!

Not installing a proper vacuum relief valve, or installing it in the wrong position could result in collapsed plumbing or panel failures. A VRV should be installed at the highest point in the system whenever possible.

Collapsed pipe caused by lack of properly placed VRV.

Collapsed pipe caused by lack of properly placed VRV.

Some people erroneously believe the relief valve in a solar pool heater is there to relieve excess pressure and heat. That is not the case. Because a solar pool heater is an open loop system, expanding water and air due to heat easily escapes back to the pool, and no pressure relief is necessary. It is a vacuum (negative air pressure) that we are trying to avoid.

A good vacuum relief valve will allow air into the plumbing efficiently and allow the panels to drain quickly. VRVs can cause a bit of noise during draining, so quick draining is ideal. We use a high quality VRV that uses a simple ball and spring principle. It can be inspected and checked for proper operation easily by removing the threaded cap. This valve type is highly reliable and efficient. Other valve types are plastic with rubber bladders or brass with steel springs. Failed VRVs are a common service issue for these other valves, and we believe our design is superior in construction and operation. A failed VRV will result in water oozing out, or in severe cases pouring out in large quantities. While swapping out a VRV is easy, they can be expensive, so installing a good valve from the start is a good idea.



  1. My VR Valve is leaking at morning start up after 3 Ninutes the leak stops.Is this Valve defective, the date on the Valve is April 1st 2013.It is a 2″Valve.

    1. Author

      Some brands of VRV do have issues with oozing, especially if there is not enough pressure to close them fully. That’s why we use a high-quality spring and ball type valve. It is much more reliable than bladder-type valves that you are probably describing. If you are in our service area, we may be able to replace your VRV with something better. We would need more information about who installed your system. Call us!

  2. so why when the panels drain (air let into the system) does my chlorinator drain also? The chlorinator is installed last right before the water returns to the pool. is this normal or is something missing?

    1. Author

      Sounds normal. If the pool level is below the chlorinator (usually the case), water will drain down with air behind it. Gravity will carry water down to the pool.

  3. I have small bubble constantly when solar is in operation, could this be a faulty vrv?

    1. Author

      Hi Tom,

      It sounds exactly opposite of a fault. It sounds like it’s doing what it should. A vacuum has been created in your system and the VRV is allowing air in to prevent a collapse of the plumbing. The problem is either a dirty filter or a pump speed that is too slow (if variable speed). 99% of the time this is caused by restriction of flow from a filter that needs serious cleaning or replacement. Check out Bubbles in My Pool.

  4. Hello,

    My old vacuum relief valve broke in just one year and I wonder if I can use brass water heater vacuum relief valve for solar panels?

    Thank you

    1. Author

      While you can, we do not recommend it. They tend to corrode and fail early. One of our competitors uses them exclusively, and we do a lot of repairs. I’m not sure what kind of vacuum relief valve your system has, but breaking after one year is pretty bad. I don’t think you are in our service area, as I would love to help. I would seek out the plastic body type that has a ball and spring mechanism.

  5. Hi Jason,
    i got a vrv installed at the hight of the gutters. It seems to be a 3/4″ brass vrv. It´s also in the line back to the pool.
    pool – pump – filter – 2 way valve – solar pool heater on the roof – vrv – pool
    Does this make sence?

    1. Author

      It makes no sense to me. The VRV should always be at the highest point in a plumbing system, just like an irrigation vacuum breaker. The idea is to allow water to drain back down the solar feed line without collapsing the panels or plumbing on the roof. Think about it this way – for your vacuum relief valve to work at gutter level it would need to create a vacuum in your return line from the top of the panels to the location of the valve, which is very hard to do because it would need to lift/siphon the column of water in the return line!

      We have one competitor that puts it even lower, near ground level. I will never understand how they expect that to work effectively.

      If you cannot have the vacuum relief at the highest point due to lack of sufficient pressure in the system, a better location would be somewhere lower in the feed line system. One potential location is on the feed (lower) panel header at the opposite end from the panel feed plumbing.

      1. Author

        And by the way, I can’t stand those brass VRVs. They are prone to corrosion and leaking.

  6. Thank you for your reply. In the feed line would make sense, at the highest point it would only drain the return line but not the fields. The feed line is on the lower side of the fields and the return line at the upper.
    If i would feed it from the upper side and put the vrv on the top line it would drain all the fields but not the feeding line. I don‘t know whats the best, but how it is now i makes no sense.

  7. Author

    No, you want it on the return line – at the highest point. You are supposed to be letting air into the system. Air will follow water down both the feed and return lines. If you put it in the feed line there will be a column of water weighing down on the valve, not allowing it to open and allow air in.

  8. Hi! I have a solar system (7panels) that has the vacuum relief valve on the header of the last panel at the far end of the feeder line and not up top on the end of the first panel. Should the VRV be switched with the end cap on the top header? My system makes a lot of noise when I turn the valve on to use the solar, banging and popping not sure if its related to the VRV. Otherwise the system works fine.

    1. Author

      Your VRV is probably in the second best location. I would not change it if it drains properly, but if it takes a long time to drain and you have excessive gurgling during drainage, it would be advisable to change it.

      Your issue with the system startup is unrelated to the VRV. It is probably related to poorly secured pipes. You will always have noise because you have turbulent air and water returning from the roof to the pool, but poorly secured pipes can vibrate and cause more noise. Depending on your pool equipment it may be impractical to secure pipes in some places, but if it is enough of an annoyance, securing or re-routing plumbing is an option.

    1. Author

      Hi Thomas – I don’t recognize you as one of our clients, but if you have our type of VRV, it is quite easy to replace if you are comvortable going on the roof. It just screws in with standard pipe threads. You just need teflon tape. If you have a competing brand, it might be more difficult, but it’s usually not very hard unless you cannot find a direct replacement and need to adapt something.

    1. Author

      Unfortunately, at this time we do not sell individual components unless it’s a part we are installing locally. I’m not sure where to get our VRVs for DIY use.

  9. Hi Jason – should the VRV be completely inserted (twisted) into the pipe? Or do I not thread it all the way? A couple of weeks ago, the whole component (pipe and VRV) was blasted off the rest of the solar system when it turned on. I am thinking it was an issue where the pressure was too great and the fastener had loosened up between the pipings.

    1. Author

      It should be threaded hand-tight with teflon tape on the threads. If it blew off it was not likely what you described. I bet the system was dead-headed when all pool returns were isolated/closed and the water had nowhere to go, causing excessive pressure in the solar panels and plumbing.

  10. Author

    Sure. It’s likely that someone shut off the solar return valve or all of the pool return valves and the water had nowhere to go. This would build up pressure in the solar panels to an unacceptable level and something bad is going to happen.

  11. Every morning when the pump starts I get a lot of air being pushed out into the pool.
    Seems like it is from the Solar panels filling and then pushing the air down through the system.
    After a few minutes it will stop and then I get no more air bubbles.

    Is this normal or should there be an air release valve above the solar panels.
    I do have VRV that looks like a PVC Check Valve and do hear it sucking air when things shutdown.

    1. Author

      Rick, this is totally normal. The system should drain down to the pool each night. When the panels fill up again all of the air is pushed back to the pool. There is no air release valve on the roof (by design). There is only a vacuum release valve that lets air in (not out). If an air release valves were used, it would spurt out water each time the system filled and likely start oozing over time.

    1. Author

      Marrellen: great question. There are three potential sources of noise when a system shuts down (drains). The first is water gurgling. This is usually most evident near the valves on the wall. The drain back method may be causing n inordinate amount of noise. There will always be some noise when water moves from place to place, but sometimes it can be annoying for a long period of time if the system does not drain fast enough. Your solar installer should be able to correct or at least mitigate this issue. The second is pipes rattling if they are not secured properly. The third, and the one you seem to be describing, is that the vacuum relief valve is making noises. If there is just enough of a vacuum to open the valve, it may “chatter” while it opens and closes repeatedly. It should not last long if the system drains quickly. It is not necessarily a malfunction of the valve, but an annoyance. If it bothers you or takes a long time to stop, there are some mitigating solutions, like correcting the drainage rate or relocating the valve. Your solar professional should be able to address this concern.

  12. When the pump is on, I notice a small drip coming from the end of the vacuum relief valve. I know I can take the entire valve off, but can you just tighten the end? What can cause this. It’s about 6 years old. Thanks

    1. Author

      Some types of VRV are prone to oozing. You can’t service them. It will likely require replacement.

  13. Yesterday, while the pool pump was running with the solar heater on, my VRV began leaking ALOT, almost gushing. This solar system has been in use for about 9 years without any issues. Thinking of replacing the VRV, but wondering if something else would cause it to leak like this? Thanks in advance for any info. Definitely not in your service area (Baton Rouge!)

    1. Author

      That’s impossible to say without investigating. It could be a cracked fitting. I don’t know what kind of VRV you have or how it is connected. I’d come over if it was about 800 miles closer! 🙂

  14. Jason, How does the entire panel system drain to the pool when not in use if the supply is checked in ? The return is at the highest point of the system… so wouldn’t there be a considerable amount of water still trapped in the supply or does the VRV create enough air to suck most of the water down the return ?

    1. Author

      There is a small hole or a built in reverse check valve in the solar bypass valve to allow water to drain down the supply line through the bypass tee and to the pool returns.

      Pentair makes a solar 3-way valve for this purpose. A small hole drilled in a standard 3-way valve also does the trick. That’s the reason a feed line isolation valve is required – for positive isolation needs.

  15. What is the proper size hole to be drilled in the three-way valve for drainage purposes ? I need to drill one today . I have a 2″ 3 way valve.

  16. Also, I installed a Heliocol system. Just got everything up & running. The issue I’m seeing is the flow rate is way to high. Flow meter is reading about 90GPM… From my homework I want it to be running @ about 40 GPM for the water to get heated properly. Right now I believe it is going through the panels way to fast to be heated. I tried throttling down the ball valve on the supply line going up the side of my house to the panels but it doesn’t do much. Not only that… my filter pressure jumped up to about 25psi, it was running at around 10psi with brand new cartridges before hooking up the solar today. Any ideas ??

  17. Author

    Hi Phil. Sorry for the delayed response. A 3/16″ drill bit would normally be sufficient. Anything smaller and you get slow draining. Larger, you may get too much water bypass.

    I’m not sure why you want to slow down the water flow. I don’t know how many panels you have or what size they are, but higher flow rate is better. 90 GPM is pretty high flow, and would be excellent flow for twelve 4×12 panels. You do not want to restrict flow. You can either allow some water to bypass the solar during operation or reduce the pump speed if you have a variable speed pump (which is highly recommended).

    For more commentary on flow rates, see this link: https://floridasolardesigngroup.com/?s=flow+rate

  18. Author

    Your minimum recommended flow rate would be 40 GPM, but 60GPM would maximize performance. Anything over that you will not likely have any negative effects with solar performance, but you’re wasting energy by pumping more water than required. That’s where a variable speed pump can pay for itself.

  19. Also, any idea why my filter pressure is running so high ? 25-30psi seems way to high. I’d assume it’s because the water is being restricted traveling through the small tubes on the panels

  20. Author

    If it’s running at 10 PSI with the solar off and 25 PSI with the solar on, something is wrong. The flow restriction in Heliocol panels is less than most competitors out there (bot more than ours). The 1.5″ plumbing is pretty restrictive, but you should have nowhere near a 15 PSI increase. 5 PSI is more typical. I would need to know a lot more about your installation to provide true consultation, however. Are you sure you have valves in the correct position? 25 – 30 PSI is close to essentially deadheading your pump (zero flow).

  21. 2 HP Hayward pump, all 2″ piping, distance fr. Equipment to panel supply is roughly 50′ & a little over 16′ up the side of the house. What other info would help ?? & valves are100% in the right position

  22. I have a feeling a variable speed pump will be the answer

  23. Author

    Most likely. What you are describing is not at all normal, but the Helicol’s smaller headers could presumably be causing the excessive pressure at that flow rate. Regardless, 90 GPM for a residential pool is overkill and energy intensive.

  24. I’ll have to do some more homework on it. & probably but an inteliflow variable speed pump. Thx for taking the time to help & sharing your knowledge. Greatly appreciated !

  25. Should we hear rushing water in the return and a ‘whistling’ VRV or is that perhaps a sign of too little pump pressure to make the 40′ head to the top of the solar on our house. Trying to tune new variable speed pump.

    Rob in NorCal

    1. Author

      A whistling VRV would result in air returning to the pool in the form of small bubbles. If that’s what you have, you likely need more flow (pressure) to close the VRV.

  26. Jason, if I currently have a 2hp Hayward pump & I want to switch to a variable speed pump… What Size Variable speed should I be looking for ? Remember fr. Our previous convos that my GPM’s are up around 90 with my single speed 2hp pump . I want to get the GPM’s in the 40-60 Range when running through my panels. I’m leaning toward a Hayward 1.6 hp VS being I have Hayward controls & equipment already.
    Pool Info:
    -17,500 Gallons , including built in spa
    -2″ pipe
    – 8, HC50 (4X12) Heliocol solar panels (2″ headers)
    – aprox 50′ of pipe underground for supply & return (100′ total)
    – aprox 20′ up the side of house for supply & return (40′ total)
    – currently running @90 GPM through solar
    With 2hp Hayward pump

    1. Author

      The answer depends on your exact automation system, but generally, we recommend the Pentair Intelliflo VSF. In your case you would also need the Intellicomm II interface probably. You might ask why we recommend a 3 HP pump, but the answer is actually pretty simple. I recommend you search our blog for information on this. Here are two links that may help:


      If you go with a Hayward pump to match your controller I highly recommend you stick with the Ecostar only. The same rationale applies to all brands. “Oversizing” has lots of advantages for not a lot more money.

  27. Understood. I just didn’t want to go to big & Have the same problem with GPM’s at the lowest speed & not be able to get them low enough. Or go too small & have to run it at the highest speed to achieve the proper GPM’s… If that makes sense. I’m trying to figure out the proper size to achieve the GPM’S & still be energy efficient at the same time

    1. Author

      The Pentair Intelliflo goes all the way down to 450 GPM. You will not have a problem with too much flow. Getting a larger HP pump allows you to run it at a lower speed to achieve the desired flow rate, reducing heat, extending life, and keeping it ultra quiet. In a physics sense, work is work. Your pumping costs for a given flow rate will be pretty much the same regardless of pump horsepower rating (all else being equal).

  28. Why is my air/vacuum valve slowly leaking by when the solar water heating system is in use. Could this be a sign that the valve needs replacement.

    1. Author

      I don’t see you in our database, so I assume you are not our existing customer, but I can answer your question in general terms. VRVs come in a variety of designs. Some are more prone to leaking. Leaking often occurs when the pressure in the system is not sufficient, or just on the edge of being sufficient. The valve is on the cusp of allowing air in, but it lets water out instead. Increasing the pressure may relieve the issue (cleaning or replacing your filter is one way to do this). Other times, the seal in the VRV may be bad, or debris may be lodged in the valve and can permanently damage the seal.

      In any case, you should have your system serviced by an expert. The valve should probably be replaced unless the issue is traced to an obvious flow issue.

  29. Yesterday we turned on the roof heating and there were a lot of bubbles in the pool (it seemed as ifthe wtare pressure was very strong), but otherwise it worked fine.
    Today, after about 20 seconds there is air hissing from a part of a vacuum valve and soon after the water starts coming out of it.
    When we turn off the heating, everything works fine, there are no bubbles in the pool.
    Filter pressure is good whether or not we use the roof heating.
    Thank you!

    1. Author

      Hi Maia,

      I don’t see you in our database, so I assume you have a competitor’s system. It sounds like your vacuum relief valve gas failed. If you are in our service area please call our office at 239-491-8010 to set up a service call. We can usually replace faulty valves with one of our long lasting ones.

  30. Hi Jason,

    My air/vacuum relief valve has been leaking for some time. The solar system is about 6 years old. The valve is located at the highest point but is mounted horizontally. Should it always be mounted vertically or does this not matter?

    1. Author

      It depends on what kind of vacuum relief valve you have. Most spring-type valves can be mounted in any orientation, but some can develop oozing leaks if not mounted vertically, or at least close to vertically.

  31. How long should it take to drain 6 panels? I have 4 panels on one section of roof and 2 panels in another section. Does each section need a VRV?

    1. Author

      Brian, that is not possible to answer accurately and definitively. Each system will be different based on pressures and plumbing lengths. Even within a system, depending on which return valves are open the answer could differ. The type and size of drain hole or bypass would also impact the answer. Most systems drain in 5 to 30 minutes. Proper plumbing would only require one VRV at the highest point in the system, but additional valves could aid in faster drainage depending on the scenario. We don’t recommend it.

  32. Hello. I have a small pool with only two solar panels. I get the normal amount of bubbles on start up that stop within a minute or so. At any given time if I turn the diverter a couple of notches from center to increase the flow to the panels I get a flood of warm bubbles that soon cool but never stop until I turn the diverter back. I thought at first it was trapped air but it never stops. All the panels are cool to the touch and I tried moving the VRV but no help. I just cleaned the filter and it’s in good shape. There are no visible leaks. Could you explain to me why this is happening. The solar panels were just installed and I just want to make sure they’re working efficiently.

    1. Author

      Hi William, I believe you are out west and not our client, but I am happy to try to help. I’m not quite following what you are saying. If you start up the system and the bubbles stop, the diverter valve would be all the way open. You say you then turn the diverter a couple of notches to increase the flow. If you turn the diverter a couple of notches you would be decreasing the flow (closing the valve). Naturally, you would get bubbles at this point because you are reducing the flow and the pressure at the VRV allowing air into the system. You definitely don’t want to reduce the flow to your solar panels. More flow means more heat – more efficiency.

      Maybe I’m misunderstanding your question. Could you elaborate on what you are doing with the diverter valve?

  33. Nice, article, thanks. I understand the purpose of this vacuum release valve, but do I ned to also add a second one, an air release valve in order to evacuate possible air that will be stucked on the highest part of the panels and can not leave the panels automatically to the pool?

    1. Author

      Hi Gerardo,

      No air release valve is required. The air is purged back to the pool return jets. With proper flow, all of the air is forced out after one or two minutes in most systems.

  34. I noticed water dripping off my patio flat roof yesterday while it had not rained. Today I went up to see if one of the panels started leaking. What I found was water coming out of the vacuum relief valve. Not a lot, but some. Does this indicate that it needs to be replaced, or could it just need to be flushed out from possible debris?

    1. Author

      Frank: I don’t see you in our database, so you probably have another brand of VRV. Most are not serviceable. Ours can be cleaned if the o-ring has become fouled, but usually, VRVs need to be replaced if they are oozing water.

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