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PEX tube used in a heating system

Hi Everyone,
I know that PEX is extensively used in low temperature radiant heat systems. I have read that it is rated for a max of 200 deg F. I am re-piping my single zone radiator hot water system into two zones. Currently, the system uses black pipe and I am wondering if I can use PEX to reconnect and rezone some of the radiators. I am planning on using black pipe or copper around the boiler, circulators and the valves, but PEX sure would be nice to tie into the existing system.
Does anyone have any experience using PEX in a hot water system? Thanks in advance for all your suggestions and help.

Re: PEX tube used in a heating system

Yes, PEX usage has become popular in retrofits of a radiator hot water system in recent years due to its low cost compared to copper tubing, which has shot up in price.

TOH plumbing expert Richard Trethewey has done a number of episodes on these retrofits that show how it is done & includes photos of stringing the PEX, usually from a copper manifold nailed to a piece of plywood against a wall where the boiler is located & zone valves or zone circulators are added there---PEX is then used to switch to the distribution lines to and from the individual radiators---the flexibility of the PEX makes it lots easier than copper to route the lines thru & around floor joists & thru walls to a 2nd floor, if needed.

I find the Taco 571 series (and later model) zone valves coming right off the copper manifold easy to work with & they are very reliable & will last for years, but some installers prefer zone circulators---2 zone valves can be used with the existing single circulator for a low-cost installation.

The biggest expense will involve the PEX to radiator connectors which are of various types---a visit to several of your local Heating Supply houses should be made once you have your detailed diagram drawn to indicate how many connectors & all other components you will need, to price the cost of these connectors, as the price varies widely---HD carries these connectors, but charges much more than a parts houses.

Taco has diagrams on how these zone systems are set up, or you can call them at their technical or e-mail numbers for detailed diagrams---generally you will have to modify your current system from a single zone, to repipe the tubing into 2 separate pipes---one for upstairs, one for downstairs (diverging at the supply manifold)---one circulator, 2 zone valves, 2 thermostats (one upstairs, one downstairs), one small 40 va xformer to drive both zone valve plungers, & converging back again using a "Y" connector at the boiler main return.

Google "zone valve installation" for more sites.


Timothy Miller
Re: PEX tube used in a heating system

Howdy consider (pex al pex) have to get it outside USA. Canada sells lots of it... It is pex then a coating of aluminum and a layer of pex. Fergesen Plumbing Supply has a version similar in the USA they can tell the heat rating sorry i do not know it.

Re: PEX tube used in a heating system

Thank you. Is there any advantage to using PEX-AL-PEX vs. PEX-A type? Or is it only an issue of flexibility?

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