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Thread: Bypass for heater

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    Bypass for heater

    Hi All,

    Just a question. I am plumbing in a new heater into my system. 250k btu hayward heater. The diagrams for installing mention nothing of a bypass for the heater but in many diagrams I see there is a bypass of the heater with a valve in it. Is this necessary or not? If it is good is there any harm in having it bypass all the time when the heater is not in use. Does this help in keeping the pool heater to last longer since there won't be as much chlorine going through it. (Just picturing putting valves on the supply and return side of the heater so it can be compltley removed from the flow of water when not in use? Any help is appreciated.

    Thanks
    25K Gallon 18X36 Vinyl Inground
    1HP Hayward Super 2 pump, Hayward Sand Filter,Hayward 250BTU Heater

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    mas985's Avatar
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    Re: Bypass for heater

    Quote Originally Posted by turnerj42
    Hi All,

    Just a question. I am plumbing in a new heater into my system. 250k btu hayward heater. The diagrams for installing mention nothing of a bypass for the heater but in many diagrams I see there is a bypass of the heater with a valve in it. Is this necessary or not? If it is good is there any harm in having it bypass all the time when the heater is not in use. Does this help in keeping the pool heater to last longer since there won't be as much chlorine going through it. (Just picturing putting valves on the supply and return side of the heater so it can be compltley removed from the flow of water when not in use? Any help is appreciated.

    Thanks
    Most heaters these days have a bypass built-in bypass so at high flow rates most of the water does not go through the heat exchanger anyway. They are spring loaded and auto adjusting but they usually have a maximum flow rate specification as well. Most Haywards are around 125 GPM so if you plan on exceeding that, which is unlikely, then it is good to have a separate bypass. There might be a very small gain in head loss with a separate bypass but again it is really not necessary. But double check the manual to make sure yours does have a bypass built-in.

    As for chemicals, I'm not sure that there is any evidence, although a lot of opinions, that bypassing the heater will in anyway lengthen the life of the heater. It is impossible to remove all of the water or chemicals from the heat exchanger and you really don't want stagnant water left in there anyway, so I don't see the benefit. The best thing you can do is to keep the pool balanced and to inject chlorine after the heater.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater, ThePoolCleaner

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    JasonLion's Avatar
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    Re: Bypass for heater

    Having a bypass is required if your pump is very large relative to the size of your heater, which is rather rare, but sometimes happens when you have a single pump for both the pool and spa. The rest of the time having a bypass is only rather rarely useful.

    You never want to turn water to the heater off completely for very long. The water left in the heater would "go bad" and then possibly cause problems when the heater was turned on again. Aside from the very high flow situation, the only real reason to bypass the heater is when you need to make the water very acidic for some reason.

    You can get a very small efficiency improvement by partially bypassing the heater when it is off, but it requires a fair bit of automation and can damage the heater if you accidentally turn the heater on when it is bypassed.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  4. Back To Top    #4

    Re: Bypass for heater

    Thank you very much for the quick replies. I may just leave it out then. my heater has an internal bypass as it states in the
    manual anyways. its a new hayward eletronic ingnition 250k. Also I have a 1hp super 2 pump so I won't be pushing the limits anyways of max flow. thanks agian for the informative answers.
    25K Gallon 18X36 Vinyl Inground
    1HP Hayward Super 2 pump, Hayward Sand Filter,Hayward 250BTU Heater

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    Re: Bypass for heater

    Not to be argumentative, but I am getting ready to install a heater and a 3 way valve to bypass the heater. The reasons to bypass the heater are: 1) if my chemistry goes bad, 2) while vacuuming the pool, I'll want better flow and avoid the added restriction of the heater, and 3) if the heater needs to be taken out of the system for servicing or whatever, I can still run my pump and filter. 4) In the middle of summer when the water is hot enough without the heater, you can avoid running chlorinated water thru.
    Having read what is posted here and on other boards about "water going bad or stagnant" I called Hayward directly to confirm. The tech from Hayward said that they are getting many questions regarding this type of setup (3 way valve to bypass the heater) and he said that even though it's not a recommendation, they feel that it’s a smart idea… and he added that it would be helpful the reasons I posted above.. I then asked about stagnant water in the heater and he sees no downside to that. He did offer some caveats: 1) Make sure the gas pressure is correct - if it’s too low, you'll get soot build up which needs to be cleaned. 2)Be sure that the valve does not get partially closed where there is enough water flow to allow the heater to ignite, but not enough flow to keep the exchanger from getting burned out … so keep the kids away from the valve and double check the valve position before you fire the heater.
    25k gal vinyl AquaRite T-15 Raypak RP2100 Heater

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    JasonLion's Avatar
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    Re: Bypass for heater

    wetviking, welcome to TFP!

    1) Don't let that happen, the heater isn't the only thing that can be damaged when your chemistry is that far off.
    2) Bypassing the heater should not be required to vacuum, if it is then something is wrong.
    3) True, but that is very rare.
    4) There is no significant risk to the heater from chlorine in the water passing through it as long as you are using CYA.

    The only significant advantage to bypassing the heater is some improvement in efficiency when the heater is bypassed due to reduced flow resistance.

    This may vary from heater to heater, but many heaters measure pressure to detect flow. With only a single 3 way valve, or with two valves that happen to have one on and the other off, the heater is still pressurized and can still turn on. Should the heater run without flow it is quite possible for it to destroy it's self. Turning the heater on by accident when it is bypassed, or the valve is in some incorrect intermediate position, seems unlikely, but you only need to do it once to regret having installed the bypass.

    Don't take what I am saying to indicate that no one should ever install a heater bypass. If you have some solid reason for wanting a heater bypass then go ahead and install one. Just keep in mind that there are disadvantages along with the advantages, and make sure that your reason for wanting a bypass out weighs the risk.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Bypass for heater

    Quote Originally Posted by JasonLion View Post
    wetviking, welcome to TFP!

    1) Don't let that happen, the heater isn't the only thing that can be damaged when your chemistry is that far off.
    2) Bypassing the heater should not be required to vacuum, if it is then something is wrong.
    3) True, but that is very rare.
    4) There is no significant risk to the heater from chlorine in the water passing through it as long as you are using CYA.

    The only significant advantage to bypassing the heater is some improvement in efficiency when the heater is bypassed due to reduced flow resistance.

    This may vary from heater to heater, but many heaters measure pressure to detect flow. With only a single 3 way valve, or with two valves that happen to have one on and the other off, the heater is still pressurized and can still turn on. Should the heater run without flow it is quite possible for it to destroy it's self. Turning the heater on by accident when it is bypassed, or the valve is in some incorrect intermediate position, seems unlikely, but you only need to do it once to regret having installed the bypass.

    Don't take what I am saying to indicate that no one should ever install a heater bypass. If you have some solid reason for wanting a heater bypass then go ahead and install one. Just keep in mind that there are disadvantages along with the advantages, and make sure that your reason for wanting a bypass out weighs the risk.

    I am getting ready to install a bypass for a reason other than those mentioned in this thread. I plan to use Jack's Magic Copper and Scale remove and it will destroy a copper heater core so you need to bypass before treatment. This is the only reason I am installing the bypass but it could come in handy in the future if my heat core blows out and I need to keep the system running.

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