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Thread: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

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    Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    I cannot hold my hand close to air exhaust - what a waste of heat?
    I am planing to run metal pipe over the air exhaust with outflow water from the heater to collect/recover some heat.
    I also think to run the return pipe to the pool above the ground. What is the reason to loose heat to the ground? This is why a pool gets warmed closer to night when the ground returns sun heat to the pipes.

    What metal pipe will be safe for the pool chemistry?
    Will the Galvanized Steel Pipe work?
    in-ground 20'000 gal; AK60431 cartridge filter x 4; Pentair MiniMax NT heater

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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    I doubt you will recover enough heat to make the effort worth while. In order to recover the heat you need to install a secondary heat exchanger. doing this will not be easy or cheap. This is how high efficiency condensing furnaces work. Everything associated with the secondary heat exchanger must be made from stainless steel as the condensation you produce is very acidic. In fact, this is one reason most pool heater manufacturers caution against running water thru the heater below a certain temp. They have found that those lower water temps (when the heat is on) is what causes the condensation to build up soot deposits inside the heat exchanger and clog them up. I fight this problem up here in the cold north all the time on home heating boilers as well as pool heaters
    Unknown make 18' above ground (bought used in 1999) Sparco sand filter. Hayward 100,000 BTu heater. 2 speed pump

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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    Quote Originally Posted by danpik View Post
    the condensation you produce is very acidic. In fact, this is one reason most pool heater manufacturers caution against running water thru the heater below a certain temp. They have found that those lower water temps (when the heat is on) is what causes the condensation to build up soot deposits inside the heat exchanger and clog them up. I fight this problem up here in the cold north all the time on home heating boilers as well as pool heaters
    Why is the condensation is very acidic? CO2 + H20 = H2CO3 - weak acid
    I worry more about chemicals inside the pipe. How they will handle the high temperature? They make a heat exchanger in pool heaters from PVC and cover with metal coil (which handles H2CO3). Why not the stainless steel heat exchanger?
    in-ground 20'000 gal; AK60431 cartridge filter x 4; Pentair MiniMax NT heater

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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    Can't say as I have ever seen a pvc heat exchanger in a heater. I do recall seeing alot of copper exchangers though.
    Over 30 years in the pool business
    We build vinyl, fiberglass, stainless steel pools
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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    Quote Originally Posted by pool123 View Post
    Why is the condensation is very acidic? CO2 + H20 = H2CO3 - weak acid
    I worry more about chemicals inside the pipe. How they will handle the high temperature? They make a heat exchanger in pool heaters from PVC and cover with metal coil (which handles H2CO3). Why not the stainless steel heat exchanger?
    Well, honestly, I can't really answer the question of acidic level as I am not a chemist. I refer that to my daughter, she's the chemistry major. I do know that when the home heating industry started messing with condensing heaters they had all sorts of problems until the material usage was sorted out.

    I guess I need to re-post my disclaimer... My area of expertise when it comes to heating systems is primarily geared toward home heating systems, primarily boilers. since pool heaters are nothing more in principle than a home heating boiler in there function I try to help out here as much as possible with questions regarding there operation and troubleshooting. Some of the components are even similar. In my area, the pool stores don't have good service techs so I have carved out a small nitch business servicing them.

    What I do know is what you want to do is possible. The heater may not like it. Cooling the output temp of the exhaust gas will change the way it flows. A couple of years ago, a local guy tried something similar with his heater. This was a chimney based heater that had a 6" flue stack exiting the top. He decided to wrap a coil of copper pipe inside the stack to pre-warm some of the water coming into the heater. It worked real well. Unfortunately the amount of water that condensed out of the flue gas rusted out the internals of the heater within 3-4 weeks along with the flue stack
    Unknown make 18' above ground (bought used in 1999) Sparco sand filter. Hayward 100,000 BTu heater. 2 speed pump

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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    If the heat was substantial enough to gain some increase in water temp, the manufacturers would have already designed the unit to have it. I doubt you would gain much more heated water thru the exhaust. To get any transfer of the heat you need to use copper or some metal.
    Paul
    http://www.gastekservices.com A word of caution: When working with gas and electrical you might want to consider a licensed contractor. Consider the value of your life and others around you. If you would like to provide a review of the help I provided, please use the following link to leave a review. gastek - Google Search,

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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    Quote Originally Posted by ps0303 View Post
    If the heat was substantial enough to gain some increase in water temp, the manufacturers would have already designed the unit to have it. I doubt you would gain much more heated water thru the exhaust. To get any transfer of the heat you need to use copper or some metal.
    Very true. Most of these heaters run in the 80% efficiency range. The best, high end, boilers are now something near 97%. The cost of a 100,000 BTU 80% boiler for me is roughly $600. a 97% Weil McClain is around $1800. This is due to the materials and control circuits in them. Most areas I now can not install anything less than 93% efficient but, pools are not regulated
    Unknown make 18' above ground (bought used in 1999) Sparco sand filter. Hayward 100,000 BTu heater. 2 speed pump

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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    They make high efficiency heaters that capture the exhaust heat. If this is a big issue for you, you should switch to a heater that was designed to work this way right from the start.

    Attempting to convert a normal heater into a high efficiency heater as you describe is very dangerous. Not only is the condensate very corrosive, but the heat that normally carries the non-breathable exhaust gases aways from the area is not present and those gases, which can't be breathed, can accumulate causing health risks. What you propose is also a violation of building codes, which are quite strict about heater venting.
    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: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    I looked in the manual. This unit can be installed inside of a house. The exhaust has to redirected outside by pipes. Those pipes will have condensate too.
    My idea was to keep heater outside but redirect the exhaust for 2 reasons:
    1) Why would you design the exhaust window on the top? for rain and debris to fall in?
    2) I hate to waste energy. I would run a small pump and try to collect heat for a small shower by the pool. Maybe together with a small solar heat exchanger.

    - - - Updated - - -

    Here is an interesting table:



    So, wood or gas...

    I am surprised why electricity has maximum efficiency and high cost. Overpriced electricity, or underpriced gas?
    in-ground 20'000 gal; AK60431 cartridge filter x 4; Pentair MiniMax NT heater

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    Re: Pentair MiniMax NT - pool heater water outflow and hot air exhaust

    As stated before this is both very dangerous and a code violation. I am locking this thread. Further discussion of this topic is not appropriate.
    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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