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_thermoplastic_pipe_for_transport_of_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
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