Are main drains necessary?

[pjt]

Are main drains necessary in an in-ground pool? I almost never use mine. I would think a second skimmer would give more benefit. If you ever needed to drain, you could use a submersible pump. Seems like you could skip the main drain to save some money on the initial build and simplify your plumbing as well.

 

[mknauss]

You are correct.

 

[Jimrahbe]

pjt,

I have a couple of rent houses without operating Main Drains. They have been that way for about five years, or more, and I have never found a need to make them operational...

Not really sure it would save any money up front, but if not there at all, it would eliminate any possible main drain issues later in life.

Thanks for posting,

Jim R.

 

[JoyfulNoise]

Main drains are a bit of an anachronism in pool design - they originated from way back in the days when pools were designed to be literally drained by opening up the main drain plug and letting the water drain to a lower elevation by gravity alone. Think of it like a bathtub drain as pools back in the days before chlorination had to be drained quite regularly. Then, as plumbing, pumps and chemistry modernized a bit, the main drain got tied into the plumbing system to try to make circulation patterns more efficient. On a small residential pool, they are not terribly useful. On larger public/commercial pools, they do help to improve circulation patterns and chemical distribution. In European and German commercial pool standards, low chlorine regulations forces pools to need very efficient circulation systems so that turnover rate can be properly controlled; in that scenario, floor drains and/or wall drains are critical to the design.

So for residential pool design, they become a thing that is "nice to have" but not necessary. They can be made more useful if the PB/plumber is willing to cross-connect them to the return lines of the plumbing system so that you could send return water back up the main drain (in the case of heated pool water). However, that takes a lot of thought to do it correctly and few PBs are willing to go down that road. The obvious downside to a main drain are potential leaks in the future especially with vinyl liner pools as they can be both a plumbing leak and a leak in the seal between the drain and the vinyl liner.

 

[tim5055]

As Matt says, I find my main drain nice to have. In the warmer months when evaporation is high I find it necessary to close my skimmers and draw from the main drain if I go out of town for more than a few days. High evaporation can draw the water level down below,the skimmer mouth and suck air into the system.

 

[JodieM]

I just went through this with my pool builder quotes. My last 2 homes with pools did not have Main drains, just 2 skimmers and a booster pump to operate a Polairis pool cleaner. One of the pool builders would not build me a pool with out a main drain, she said it was a law to have one and the pool would fail inspection. I read every state and county code and the only mention of main drains for residential pools was to comply with the VGB 2 drain safety law. We found a builder that was willing to work with us. They thought I was really strange not to want a Main for circulation, but honestly the Polaris moves my lower water enough that I never had chemical or debris issues.

 

[bizzle]

They can be made more useful if the PB/plumber is willing to cross-connect them to the return lines of the plumbing system so that you could send return water back up the main drain (in the case of heated pool water). However, that takes a lot of thought to do it correctly and few PBs are willing to go down that road.

If we don't find a use for the main drain in our pool, is it as simple as replumbing the main drain with the returns? Or is that going to cause issues?

 

[JoyfulNoise]

If we don't find a use for the main drain in our pool, is it as simple as replumbing the main drain with the returns? Or is that going to cause issues?

You can replumb it as long as the main drain is not attached in series to a skimmer (mine is). Just make sure that it has its own adjustable shut off valve so you can adjust the flow. There’s going to be more hydraulic resistance to pumping water up through the MD than to the wall returns so being able to split the flow and independently adjust it will be a good way to redo it. The only time you would really want a lot of flow to the main drain is when heating the pool water is being heated. Otherwise you can send most of the water to the wall returns.

 

[sktn77a]

I don't have a main drain in my 20 year old pool. I am in the process of having it renovated and two of the builders INSISTED I had to have 2 main drains installed (to be in compliance with VGB). I've read the VGB rulings and they do not require two main drains to be installed if you don't have one to start with. But they wouldn't budge so I went with a different builder.

Yes, a main drain does have some merit (emptying the pool, dropping the water below the skimmer for winterizing, sucking in dirt, etc, that falls to the bottom of the pool) but most of these can be handled with a small sump pump.

 

[PoolguyinCT]

I just went through the above with a misinformed local building inspector & had a favorable ruling with state..
in CTVGB is not a applicable to residential for retrofit.. as a parent I wish it were, as a contractor it would be too laborious.
I have a self imposed ruling on my pools with wall suctions- I dead head them or reverse flow.

 

[Thorvald]

Well I'll toss in my 2 cents as well. Just had a pool built and absolutely love the main drain. Compared to my neighbors that have to shut their pumps off while away (due to excessive leaves etc) I can leave mine running I just change my schedule to use 100% main drain while away.

Now of course one thing I love about main drains that my builder unfortunately did not do was install the second line that is supposed to go to your skimmer with the valve. So that if your skimmer plugs up or runs dry, it automatically pulls from the main drain. However I don't mind too much since the automation system lets me work around that.

I have a schedule during the normal part of summer (no leaves) that alternates between the skimmer and main drain each day for a few hours to change up the circulation.

Heard alot of horror stories about main drains but happy here.

Cheers
Tim

 

[tstex]

Interesting thread...I have 2 main drains in the deep [5 1/2 ft] end and 2 wall drains for the scuppers w super ii pump. my 2 skimmer returns are linked to the main drains so I can select a 50-50 or 70-30., etc return to pump ratio. I keep them about 90% on skimmers bc I want better water flow and more effective cleaning of pool surface and less resistance for pump to pull water from surface where skimmers are located, rather than deep end.

Matt [Joyful Noise], "anachronism in pool design", what a choice word for the situation. I kind of find myself as an anachronism bc I like and prefer the simplicity of decades prior to now...I tell my wife that all the time, "keep in real simple..." LOL

I would assume that you channel more water via the MD when heating the pool since the cooler water resides at the bottom, thus preventing a thermal w hot on top and cooler or much less warmer on the bottom that is not being as effectively re-circulated if done via the skimmers, yes?

Finally, less holes in the pool would surely reduce any chance of a future water leaks, esp when PVC or other is attached, and more so if your soil is clay and has a proclivity to shift during extreme droughts and then excessive rains. In 2011, we had 15-20 inches annual total during drought; then H-Harvey dropped over 3 ft in 3-4 days...we could exceed 65-70" this year....

Best to all,
tstex

 

[pooldv]

I also like my bottom drain for a couple of reasons. Like Thorvald, we have lots of trees that fill up the skimmers at times. Our bottom drain isnt tied I to the skimmers but there is a 3-way at the pump that selects all drain, all skimmers or blend. I leave the valve set to 80% skimmer and 20% drain so that when the skimmers are packed full of leaves the pump can draw water from the bottom drain. Also, when brushing the poolie is easy to push the "dust" to the drain to be sucked up to the filter rather than vacuuming.

 

[cfherrman]

After only running two main drains on my pool this summer with no way to clean the bottom of the pool other than a brush, there is no way I would ever not have drains in the future

 

[rynoshark]

For those with an inline main drain via the skimmer and a single return, I wonder if it is possible to replace the existing return with a skimmer and then somehow replace the existing skimmer/main drain inline setup to a return (coming out the old skimmer). I have concrete over top of everything, so it seems like a minimal modification to change the existing return to be a skimmer might be possible. Then you'd have the benefit of being able to route some of the return down the existing main drain in the "old" skimmer and let the rest return out via the old skimmer hole. Or is this crazy? Seems like a positive retrofit that someone should produce to make pools safer AND change the main drain to a return.

Basically an insert for a Hayward skimmer with main drain holes, that replaces it with a return connection from skimmer inlet to main drain and to an insert that plugs into the wier hole with a return jet going out. Then you install a new skimmer hole where the old return is, making that your new skimmer. And, finally, reversing pipes in pool house. Crazy?

 

[mclifford]

A pool builder in our area simply recommend the drains because debris collects in the deep end and it would help with cleaning.

 

[Jeff Lebowski]

I just stumbled across this thread. Interesting read to be sure as I have a pool with a main that appears to be inoperative, and I wanted to post a few questions. I'm getting my learn on!

I have a small pool with one main and one skimmer. I just removed a HUGE pine tree that caused me all kinds of skimmer problems. Namely, during the last Noreaster, my pump cavitated dry becasue the skimmer was totally clogged and would not allow any water to the pump.

I had assumed in this case that the main would have taken over suction duties. But it did not apparently.

I have two ball valves on the filter plumbing. One white, one red. My assumption was that one shut off the skimmer and the other shut off the main. Both are always open. The last time I tried alternatively closing them, nothing seemed to have happened. I bought the pool along with the house, so I know little of its construction and have zero in the way of schematics or info.

I would like my main drain to function properly to prevent what just happened. I have already removed the tree, but my neighbor has a bunch of them and the prevailing breeze brings her trash my way. Plus, my pool tends to get a lot of particulate that winds up on the bottom due to its close proximity to my gardens. And, it seems to puke a little DE each time I fire it up in the spring. I'd like to be able to push that detritus into the bottom drain, but I don't think that it works.