RO unit cold vs hot water.

[Seasonedreefer]

Why cold vs hot water? I have always heard cold water and have always used it but just for giggles I ran it from the hot water side still zero TDS and it produced water twice as fast! It made me wonder why does everyone run RO units off the cold water?

 

[btkrausen]

I've read that people use hot water buckets to run the water through before it goes through the RO unit and it helps create water faster. There might be some "ideal" temperature that RO membranes work the most efficient at, but then again, warmer water could "open" it up more, allowing more bad stuff to come out.

 

[subielover]

I may be wrong but I believe running hot water through the unit will cause the membrane to become exhausted.

 

[Seasonedreefer]

I've read that people use hot water buckets to run the water through before it goes through the RO unit and it helps create water faster. There might be some "ideal" temperature that RO membranes work the most efficient at, but then again, warmer water could "open" it up more, allowing more bad stuff to come out.

This maybe true but zero TDS is Zero TDS right?

 

[greg0385]

that and the expense of the hot water heater heating the water, might not be much but on large containers could add to be a extra expense per month vs cold.

 

[btkrausen]

This maybe true but zero TDS is Zero TDS right?

But I wonder, like said above, if it would exhaust the membrane faster? You would get a good answer from Russ at BuckeyeFieldSupply.com, as he knows his stuff.

 

[drainbamage]

main reason not to use hot water is because of all the sediments sitting in the bottom of your hot water tank- you're right, you'll get the same 0 TDS as your RO and DI unit remove all those sediments- but you're just going to end up paying more for the hot water, the pre-filters you burn through, the RO membrane getting chewed up, and the DI becoming exhausted faster.

If you have an 'instant' hot water device that works like a reverse radiator, that's a hole different ball game and then yes, you can definitely use 'warm' water to get a much faster production rate (as the water is warmer, all the molecules are 'spaced' further apart and find it much easier to pass through the RO membrane.) What people are doing with the bucket of water and a coiled line going from the cold water to the RO unit is identical to the instant hot water devices.

 

[Seasonedreefer]

Very good point about hot water heater sediment. I have always wanted that instant RO water!! and have looked at a booster pump and currently have good water pressure currently at 60psi and get good water production but I always want faster production! I mean doesn't everyone?

 

[greg0385]

i saw a neat little trick for getting the right pressure for the RODI, take the intake line and put a gatevalve or a needlevalve to a pressure gauge. turn the gatevalve down to make the pressure go up to your sastisfaction. just like putting your thumb over the end of a hose, the pressure goes up using the same amount of water with no pump. props go out to my friend Rhett Campbell.

 

[CJO]

The hot water will burn up your DI resin in no time. It's an expensive way to increase your water production. Warm water is fine.

CJ

 

[Viva'sReef]

I think you just smoked your RO membrane dude.....

Here is a statement from the RO/DI expert

AZDesertRat
Mar 26 2009, 08:58 AM
I answered this in one of your other posts but here it is again.
Never run hot water through a RO membrane. Water over 113 degrees will melt the plastic film instantly.
This goes for trying to blend or temper the water by mixing hot and cold too.
Remember being in the shower and someone flushes the stool or starts the clothes washer? You got your tush scalded! The same thing happens with the RO membrane and its not worth the risk.
Colder water affects GPD output but it can be offset by higher pressure. At times a booster pump is a good idea if you have colder waters.
Another reason to stick with the colder water is it filters better and will make the membrane more efficient since colder water is more dense and the dirty stuff does not try to pass through the membrane as much as with warmer water

 

[fsu1dolfan]

I think you just smoked your RO membrane dude.....

Here is a statement from the RO/DI expert

AZDesertRat
Mar 26 2009, 08:58 AM
I answered this in one of your other posts but here it is again.
Never run hot water through a RO membrane. Water over 113 degrees will melt the plastic film instantly.
This goes for trying to blend or temper the water by mixing hot and cold too.
Remember being in the shower and someone flushes the stool or starts the clothes washer? You got your tush scalded! The same thing happens with the RO membrane and its not worth the risk.
Colder water affects GPD output but it can be offset by higher pressure. At times a booster pump is a good idea if you have colder waters.
Another reason to stick with the colder water is it filters better and will make the membrane more efficient since colder water is more dense and the dirty stuff does not try to pass through the membrane as much as with warmer water

1+ hot water just doesnt make any sense...even warm water seems like a waste too. If not for all those reasons but the water heater alone and wasted $$$ runnning it.

 

[cparka23]

Hot water is a better solvent than cold water, so I'd venture a guess that you're causing the membrane to remove dissolved particulates that might normally be picked up by the carbon or sediment filters.

This seems like a question that should have been asked before trying it, especially if you've heard everyone saying that it should be run from the cold line. Hope you didn't damage your RO membrane in the process.

 

[btkrausen]

1+ hot water just doesnt make any sense...even warm water seems like a waste too. If not for all those reasons but the water heater alone and wasted $$$ runnning it.

Yup, this is what I mentioned with opening it up, as the warm water would let more sediment through.

 

[CJO]

The hot water will burn up your DI resin in no time. It's an expensive way to increase your water production. Warm water is fine.

CJ

Whoops, Viva's right. I meant to say RO. Hope that didn't happen. If it did, your DI is now doing all the work and won't last too long.

CJ

 

[DC_Reefer]

I head the colder water causes the membrane to be more "constricted". SO it doesn't make as much water because less water is getting through the membrane. I think this also means the TDS out is lower hence the resin would last longer.

Now all the other stuff about using water from the hot water heater and sediment makes sense but that would be a separate issue than just the temp of the water.

 

[Seasonedreefer]

RO membrane is fine I have my TDS meter set up right after the membrane and one after the DI stage. Both reading zero.

 

[CJO]

That's good news.

CJ

 

[kellyjn]

Is your water that clean to begin with? How can you get 0 out of the RO membrane? I think you might want to check your TDS meters against a seperate and different TDS meter. I've never heard of a membrane that has a 100 percent removal rate.

 

[GrampaDon]

I just looked up the "general temp vs. production rate" for RO production.
And yes the membranes are rated at 77.F degrees. And like you ,I have both the hot and cold tapped. And come into one line into my RO unit.
My production rate goes up , and the rejection rate is closer to 4 to 1 at 60.-70.F by adding just enough hot water. [My money im spending.]

But like stated b4 you can trash a RO membrane quick with HOT water.
I know since it also happened to me. Live and learn.