Thoughts about stagnant water in the heater when bypassed?

[DavidArmenB]

I notice a lot of people prefer to have bypass valves plumbed with their heaters so they can bypass the heater when not in use because, they say, it prolongs the life of the heat exchanger and because the pump uses less energy to move the same amount of water without the heater being in the line.

I, too, plumbed a bypass valve when I installed my natural gas heater recently. One thing I have been curious about is what people with more experience say about the stagnant water inside the heater when it is bypassed? Are you supposed to drain the heater every time you bypass it? Is it detrimental for the heater if the stagnant water stays in the heater for an extended period of time when it is bypassed, say, in the summer? Assume water is balanced (pH 7.4-7.6, Alkalinity 100ppm, CH 300ppm).

What are your thoughts on this subject?

 

[Silver_2000]

easy solution would be allow a trickle to not bypass
Similar to how we fixed our rock wall issue
We have a rock water fall that traps leaves and then when we do turn it on we get a dump of rotted and other leaves etc - to fix that we have the waterfall turn on every day at 6pm for 15 min
That clears out the stagnation
Also reminds me its time for a beer

 

[1poolman1]

I notice a lot of people prefer to have bypass valves plumbed with their heaters so they can bypass the heater when not in use because, they say, it prolongs the life of the heat exchanger and because the pump uses less energy to move the same amount of water without the heater being in the line.

I, too, plumbed a bypass valve when I installed my natural gas heater recently. One thing I have been curious about is what people with more experience say about the stagnant water inside the heater when it is bypassed? Are you supposed to drain the heater every time you bypass it? Is it detrimental for the heater if the stagnant water stays in the heater for an extended period of time when it is bypassed, say, in the summer? Assume water is balanced (pH 7.4-7.6, Alkalinity 100ppm, CH 300ppm).

What are your thoughts on this subject?

Last three heater schools I attended recommended that water run continuously through the heater, at least some, as Silver-2000 said. The issue is not stagnation (there's very little water in a heater at any one time) so much as the water evaporating and leaving behind deposits on the interior of the heat exchanger. Yes, they can be cleaned out, but virtually no one has the correct tools for the job. The heater top end has to be disassembled, in the case of a straight-thru heat exchanger like yours, to run a very expensive reaming tool through the tubes and then reassembled with all new gaskets and O rings. Heaters like the Pentairs, Jandys, RayPak Avia can't be done this way, if at all.

 

[DavidArmenB]

easy solution would be allow a trickle to not bypass
Similar to how we fixed our rock wall issue
We have a rock water fall that traps leaves and then when we do turn it on we get a dump of rotted and other leaves etc - to fix that we have the waterfall turn on every day at 6pm for 15 min
That clears out the stagnation
Also reminds me its time for a beer

Last three heater schools I attended recommended that water run continuously through the heater, at least some, as Silver-2000 said. The issue is not stagnation (there's very little water in a heater at any one time) so much as the water evaporating and leaving behind deposits on the interior of the heat exchanger. Yes, they can be cleaned out, but virtually no one has the correct tools for the job. The heater top end has to be disassembled, in the case of a straight-thru heat exchanger like yours, to run a very expensive reaming tool through the tubes and then reassembled with all new gaskets and O rings. Heaters like the Pentairs, Jandys, RayPak Avia can't be done this way, if at all.

Thank you so much, I set the bypass valve so a small percentage of the water constantly flows through the heater. My pump is set to run 22 hours a day at various RPMs.

 

[gkw4815]

FWIW, that's how the Jandy Versaflow heater bypass system works, ie when the heater is bypassed, the valve still allows a small portion of total flow through the heat exchanger.

 

[sktn77a]

I guess it depends on your what your concern about "stagnant" water is. If you're concerned about bacterial/algae/etc growth inside the heat exchanger, I don't think you need worry. Residual chlorine should be high enough for short term protection and, when that expires, copper ions from the heat exchanger itself should prevent growth. If you're concerned about salt precipitation (copper chloride, copper carbonate, calcium carbonate, etc) then your concerns may be justified (although I'm not sure how these would come out of solution as the heat exchanger is a closed system and water shouldn't evaporate).

 

[ajw22]

Both Jandy and Pentair now have automatic heater bypass controlled by the heater and they both leave a bit of water to circulate through the heater when the heater is bypassed.

 

[1poolman1]

I guess it depends on your what your concern about "stagnant" water is. If you're concerned about bacterial/algae/etc growth inside the heat exchanger, I don't think you need worry. Residual chlorine should be high enough for short term protection and, when that expires, copper ions from the heat exchanger itself should prevent growth. If you're concerned about salt precipitation (copper chloride, copper carbonate, calcium carbonate, etc) then your concerns may be justified (although I'm not sure how these would come out of solution as the heat exchanger is a closed system and water shouldn't evaporate).

For what it is worth, heater manufacturers would not warn about the possibility of water sitting in the heat exchanger evaporating and leaving deposits if it didn't happen at some point in their testing or the feedback they get from the field. They really do like to get good reviews and word-of-mouth advertising.

 

[proavia]

Being in Santa Clarita CA, you don't close your pool.
As long as your pool water is balanced - pH, CH and CSI in range - you could set your bypass to allow pool water to flow thru the bypass and the heater at the same time. This produces the least restriction and allows some flow thru the heater at the same time. For the few times each year the temp gets down to freezing for a couple of hours, just have the pump running to keep water moving.

The key being balanced water. Too low a pH or CH isn't good for your heater core. Follow TFP recommendations for water chemistry for best results. And don't slack off too much in winter from normal testing.

Heater bypass allows heater to be isolated from the system if the heater has a leak. It allows flow thru the heater when heating. It allows water to both flow thru (at a diminished rate) and bypass the heater for the least amount of restriction (better flow rate than running thru heater only).