12 odd years ago I accidentally ran across a used industrial copper water radiator. It can withstand city water pressure, car radiators cannot. It measures 4' x 2', I got it for the salvage price of Cu at the time, about $50. I have been looking for another one ever since and have not found one.

I have used it ever since to heat my hot greenhouse by running the water from the house water heater through it using a recirculating pump and having 3 fans behind it blowing air through the vanes. Not all the heat is dissipated into the GH as the water returning to the water heater is still pretty warm. This is why I have been looking for another radiator.

The other day a plumber friend showed me the solution. Plumb in 50' of PEX pipe and just randomly lay it on the ground of the GH. I holds heat poorly and will transmit the remaining heat. After the water goes through the radiator, it curses through 50' of 1/2" PEX pipe and now when it returns to the water heater it is no longer warm. The PEX pipe radiates the remaining heat.

I am going to use it primarily in my cold greenhouse which also needs to be heated when temps go below 45 to 50F. A 50' coil of 1/2" PEX pipe is $25 at my local outlet which is a whole lot cheaper than either a copper radiator or the floor vanes (copper/aluminum combination) commonly used. It is a perfect radiator. My plumber friend tells me that they use it instead of the conventional heating units where hot water is used as the heat source. They just lay coils of it below the floor, run hot water through it and have a floor heating unit at a fraction of the usual cost. If not all of the heat is dissipated it takes 15 minutes to add another 50 feet.

You need a special tool to force the endings into the pipe. My local outlet lets me use theirs after that it's just simply CPVC which is no problem (Don't use PVC for hot water).

Nick