Older radiator styles are soldered with lead so that isn't a good drink. The new model cars use a plastic radiator mostly glued together, might have possibilities. I personally wouldn't want to drink anything stored for a long period of time without thoroughly sterilizing the water first.
Just my 2 pennies worth

Old air conditioner coils are copper. It's a possibility.

dcarch

Not an odd question at all.

The way I would do it (the way I will be doing it next spring) would be to have a copper pipe coil in your big water tank and circulate water through that and then through your radiators.

You have a closed system, the liquid that passes through the radiators is seperate.

I have a dead window mounted AC unit that I am going to use. They contain TWO "radiators" although the pipe diameter is very small.

I dont think i would risk it for drinking. car radiators may have been put together with lead soilder. A/C coils will have oil residue in them.

More than likely new radiators will be from china or mexico and no telling what might be in them.

Use it for heating or cooling depending on where the water source is from. if underground spring it could be used for cooling in the summer. Winter time use a circulating pump with the heated water.

"A/C coils will have oil residue in them. "
A/C coil has oil with refrigerant to lubricate the compressor, but is's very easy to clean out with detergent. It's the best heat exchanger.

If you design your system correctly, say one vertical insulated pipe and one not insulated, the convection current of the water may eliminate the circulating pump.

dcarch

dcarch
As a former mechanical journeyman, i know that a/c coils are good heat exchangers. What i said was i wouldnt use one for drinking water. You are more than welcome to, if you want.

That was one part of the original question. I dont know what might be used in the construction of a coil or radiator as far as food grade material. Are they safe to use for drinking water? i have no idea and dont plan to use either as such.

Hi Kate
Another option may be to circulate the warm water through tubing in raised beds or the floor if its practical.
I think the water temperature would need to be pretty high for the radiator/fan system to work efficiently.