Heater Bypass - stagnant water question

[MarkHoop]

I am redoing my plumbing and going to add a 3 way valve to bypass the heater and a check valve on the outlet of the heater. My question is if I was to bypass the heater for say 2 weeks while away what effect does the stagnant water in the heater have on the heat exchanger if the water is properly balanced? Sorry, just a little gun shy after recent heater issues...

 

[ajw22]

Both Jandy and Pentair who have automatic heater bypass valves have it set to allow about 90% of the water bypassed but about 10% flows through the heater. That keeps the water in the heater from getting stale and the benefits are the same as if 100% was bypassed.

 

[MarkHoop]

I am going to install a manual 3 way so are you suggesting that I not close it fully and permit a small amount of water to flow through the heater at all times but instead just turn the heater off. Doesn't that defeat the purpose?

 

[ajw22]

I am going to install a manual 3 way so are you suggesting that I not close it fully and permit a small amount of water to flow through the heater at all times but instead just turn the heater off.

Correct but I don’t understand the instead part.

Doesn't that defeat the purpose?

What do you think the purpose is?

 

[MarkHoop]

The instead is to turn the heater off even though there is water flow (not really an instead)
I believe that the purpose of a 3 way is to allow heater Bypass when pool conditions are not ideal (pre-season) or when you can't monitor regularly (away from home). Am I missing anything?

 

[ajw22]

I believe that the purpose of a 3 way is to allow heater Bypass when pool conditions are not ideal (pre-season) or when you can't monitor regularly (away from home). Am I missing anything?

Those are short term reasons to fully bypass all water. For the short term until you correct the water chemistry the water getting stale in the heater will not be an issue.

Longer term people bypass their heater when they do not intend to use it to increase the efficiency of the pump and remove the resistance of the heater. For that let some water flow through it. Even while you are away from home.

 

[1poolman1]

The instead is to turn the heater off even though there is water flow (not really an instead)
I believe that the purpose of a 3 way is to allow heater Bypass when pool conditions are not ideal (pre-season) or when you can't monitor regularly (away from home). Am I missing anything?

If you block all flow to the theater, it is not stagnant water you need be concerned with, but evaporation of the water that is in the heat exchanger. When it does, all that is left are whatever dissolved solids in the water and that coating will stick to the tubes and decrease the efficiency of the heater. Thirty-plus years ago it was taught that by both Laars (now Jandy) and RayPak, if a bypass is plumbed in, always allow a small amount of water through the heater to alleviate this issue.

 

[MarkHoop]

If you block all flow to the theater, it is not stagnant water you need be concerned with, but evaporation of the water that is in the heat exchanger. When it does, all that is left are whatever dissolved solids in the water and that coating will stick to the tubes and decrease the efficiency of the heater. Thirty-plus years ago it was taught that by both Laars (now Jandy) and RayPak, if a bypass is plumbed in, always allow a small amount of water through the heater to alleviate this issue.

Interesting, honestly never thought of that. I will be installing a check valve after the heater and before the SWG (as per manufacturers manual and not because I think it is necessary) so are there any concerns over the operation of the CV?

 

[MarkHoop]

Interesting, honestly never thought of that. I will be installing a check valve after the heater and before the SWG (as per manufacturers manual and not because I think it is necessary) so are there any concerns over the operation of the CV?

Also, I was under the belief that the purpose of the 3 way valve was to provide the ability to ensure that the heater could be valved out during periods where the chemistry may not be ideal (season start up etc) to help protect the HX. Am I misunderstanding the rationale?