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Thread: Compatibility of PEX tubing w/ hot tub chemistry?

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    Gooserider's Avatar
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    Compatibility of PEX tubing w/ hot tub chemistry?

    I have a question that comes from my other life as a Mod over on Hearth.com, where we have a lot of folks that want to use their wood boilers to heat their hot tubs, as an alternative to feeding the Overpriced Electric Co...

    In the hydronic world these days, people use a lot of PEX (Cross-linked Polyethylene) tubing - it is really good for heating systems, and for domestic water supply plumbing, with a lot of advantages and a few downsides.

    One of them is that it lists a lot of chemical incompatibilities in some of the technical papers on it - including high levels of chlorine and various petrochemicals, and so forth.

    It is OK with the chlorine levels found in tap water and such, but pools generally run a lot higher, plus people often use various oils and lotions that might be a problem (and not just for the guy trying to maintain the pool chemistry! )

    I know I haven't seen any mention of using it for pool / hot tub plumbing - including just doing a search on PEX -

    Does anyone (preferably w/ pool building background) have any definitive answers on whether or not PEX tubing is compatible with pool and hot tub chemistry?

    Thanks,
    Gooserider
    Free-form Inground gunnite pool, Estimated 16-17K gallons. New Pentair TR60 ClearPro 24" sand filter and Compupool CPSC-48 SWG, Hayward SP1607X10 Pump w/ 1HP motor, 1.5" plumbing, Polaris Pressure cleaner w/ booster pump. pool is more than 25 yrs old, less than 35. Not painted, deteriorating tile surround. I am paraplegic, get in/out of pool w/ S.R. SMITH PAL portable pool lift (significantly modified)

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    Re: Compatibility of PEX tubing w/ hot tub chemistry?

    I've run a thousand miles of the stuff but never for running highly chlorinated water through it. If the specs say chlorine could harm it, i wouldnt run it.
    The more troublesome issue is trying to heat even a hot tub with wood. It will take ~100,000 BTU to heat a 400 gallon tub from 70-100 degrees. How long would a wood buring boiler take to generate that?
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    Gooserider's Avatar
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    Re: Compatibility of PEX tubing w/ hot tub chemistry?

    Did a bit more digging as I knew that I had seen stuff before on this....

    From a file I've downloaded - the "Watts-RadiantPEX-AL_Manual.pdf"
    Do not allow the tubing to come in contact with any of the following:
    – Petroleum based products
    – Pipe sealants
    – Firewall sealants
    – Kerosene
    – Gasoline
    – Fuel oils
    – Cutting oils
    – Asphalt
    – Contaminated soils or building materials.
    and
    6. Do not use in swimming pools or other systems that use high levels of chlorine.
    In the "Watts-WaterPEX_Manual.pdf" I found:
    Protect from Chemicals
    Chlorine: Except for short-term superchlorination of potable water lines when a potable water system is being cleaned, do not permit prolonged exposure of free chlorine concentrations in excess of 2 parts per million.
    I feel pretty sure that I've seen similar things from other manufacturers as well, and also tend to doubt that there would be that much difference between different brands.
    I just found this link on the resistance of different plastic pipes to chemicals, http://www.plasticpipe.org/pdf/tr-19...f_chemical.pdf It is quite a lengthy table, but according to it, PEX is not resistant to Bromine, and has only limited resistance to chlorine and chloramines in higher than drinking water concentrations. So it looks like the chemicals in our pools and tubs are stronger than PEX is good for...

    bk406

    I've run a thousand miles of the stuff but never for running highly chlorinated water through it. If the specs say chlorine could harm it, i wouldnt run it.
    The more troublesome issue is trying to heat even a hot tub with wood. It will take ~100,000 BTU to heat a 400 gallon tub from 70-100 degrees. How long would a wood buring boiler take to generate that?
    Actually not all that long with the setups that many people on Hearth.com are running - while there are some folks that are running the old-fashioned, highly polluting, and quite inefficient "Outdoor Wood Boiler (OWB)" units, we try hard to talk people out of those and into the more modern gasification boilers that are much more efficient, and very clean burning, especially when set up with an appropriate thermal storage system. Don't want to go into to many off-topic details here, if interested go to the "Boiler Room" area of the Hearth...

    However most of the time, you aren't trying to take the tub from 70-100*F, or whatever the local temp is to full cooking temps - you are trying to maintain the existing temp, which is a lot less of a demand if the tub is covered and well insulated (we also push VERY hard on the virtues of insulation!)

    It is worth noting that doing the hot tub w/ an existing boiler setup approaches "free" heating - Boilers and so on are sized for "design day" loads - or the expected coldest day in your area, which you might not even see every year. Because of the increments in boiler sizing, you almost always over-size for even that condition, and the rest of the time you are always oversized to some degree. It doesn't really cause a lot of sacrifice to use some of that extra boiler capacity to keep the tub hot. Might take a few extra loads of wood over the course of a season, but hardly enough to make a big difference.

    Just as a rough idea, we generally recommend the typical house do around a 100-150KBTU/hr gasification boiler, and about 1,000 gallons of thermal storage - under design day conditions, this usually results in needing 2 fires / day (and maybe an extra reload) to keep the house comfortably warm, and supply all needed DHW. As the weather gets warmer, the frequency of firing goes down to once every couple of days during "shoulder season" and perhaps once every 7-10 days during the Summer for those folks that use the boiler for DHW (we often suggest solar, or even going back to electric for Summer, but some folks want to stay on the boiler) Each fire will typically burn for 2-4 hours, with minimal boiler idling, and supply all house heating loads during that time, PLUS charge the thermal tank from it's minimum usable temp (typically 120-140*F) to boiler maximum of around 180-190*F. If doing all this is no big deal, keeping a well insulated 4-500g tub at the proper "people soup" temperature is no big deal...

    Only other cost besides the wood is to run a small circulator pump (usually around 40W) which beats the heck out of a several thousand Watt electric element...

    Gooserider
    Free-form Inground gunnite pool, Estimated 16-17K gallons. New Pentair TR60 ClearPro 24" sand filter and Compupool CPSC-48 SWG, Hayward SP1607X10 Pump w/ 1HP motor, 1.5" plumbing, Polaris Pressure cleaner w/ booster pump. pool is more than 25 yrs old, less than 35. Not painted, deteriorating tile surround. I am paraplegic, get in/out of pool w/ S.R. SMITH PAL portable pool lift (significantly modified)

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