Radiant floor diaphragm tanks

jimc

I've just become aware that there is a special plastic lined diaphragm tank that is specifically made for radiant systems.  I've had regular tanks fail over the years (not enough to set off alarms) from pin hole corrosion and never put 2+2 together.

I found the special tank by accident when browsing through the supply house counter books.

My question is why radiant systems need a special lined diaphragm tank?  Both tanks that failed were on Bradford White water heaters with the internal heat exchangers.  Both heat exchangers failed leaking city pressure into the radiant loops.  Both systems have air eliminators on them, hence the diaphragm tanks... 

Alan (California Radiant) Forbes

Expansion tanks

"Both systems have air eliminators on them, hence the diaphragm tanks... "



Just because you have an air eliminator doesn't mean you need an x-tank.  X-tanks are there to allow water to expand without a rise in pressure.



Bradford-White Combi-Cor water heaters are legendary for failing, but have a newly designed heat exchanger.  I haven't tried one out yet.



And as to your main question about a special x-tank for radiant, the only special one I know of is the one for potable water when non-barrier tubing has been used.  These x-tanks can tolerate water with entrained oxygen.

BobbyG

good question

the only different thing I see for it is....plastic-lined and non-ferrous connection (for barrier or non-barrier tubing - is what the brochure below says...) and is factory set for 12 psi.

The few non-barrier jobs I did before, I used a plumbing expansion tank and bled off to set air side to 12 psi.  This special "radiant" expansion tank could be used for that application.



page 4

http://www.amtrol.com/pdf/MC2680EXTROLBrochurelow.pdf

cheers.