O2 barrier pex or regular PEX & bronze pump for closed exchanger loop off DWH?

Jells

I'm heating a small apartment from it's water heater, done this before as open system circulating potable water, but I'm now trying to do it safer and use an exchanger with 2 pumps. Should I just use a bronze pump on the heater loop like I always have, or a regular cast pump and barrier PEX? The pump price difference seems like it might be worth it since I read the barrier PEX is harder to work with than standard Pex-A. There's no other O2 sensitive components in the closed loop system, just air bleeds, checks, and expansion tank.

EBEBRATT-Ed

Your creating a separate closed loop with it's own make up water and expansion tank. I don't see any need for a bronze pump or anything special

Jells

EBEBRATT-Ed said:

Your creating a separate closed loop with it's own make up water and expansion tank. I don't see any need for a bronze pump or anything special

But then if I don't use barrier PEX aren't I putting a cast pump at corrosion risk? Or is it just too little footage of PEX, I'm feeding kickspace heaters not radiant loops.

PC7060

Believe @EBEBRATT-Ed meant for you to use O2 barrier rated PEX and standard closed system pump. 

HomerJSmith

Use barrier Pex A and a cast pump which is much cheaper than a bronze pump, if a closed sys. The length of the circuit as well as the size of the tube has a lot to do with pump sizing . One usually fall within a range of 3/8" to 3/4" tubing. Pay attention to ED's comment about makeup water and expansion tank. A Fill-trol would be my choice.

If you use a flat plate heat exchanger and you use potable water, you will need two pumps. a bronze one and a cast one. If you use potable water for heating it must be done right to prevent legionnaire contamination. See: radiantec's solution.

https://www.radiantec.com/about-radiant-heating/our-heating-systems/

PC7060

HomerJSmith said:

If you use potable water for heating it must be done right to prevent legionnaire contamination. See: radiantec's solution.

https://www.radiantec.com/about-radiant-heating/our-heating-systems/

So Radiantec's potable water heating system is safe because the DHW source pulls exclusively from the Water heater where it has been heated to safe temperatures? Seems like you would need a mixing valve at the point where cold water enters the system to reduce the floor heating temp based on ODR. Not sure why you would supply outside waterline from a "pre-heated" source as shown.

Jells

Youngplumber said:

@PC7060 it's "preheated by mixing with the return water from the loop.

@HomerJSmith what happens with this sytem after two showers? Or one long one? Do you just temporarily lose some heating capacity? 

I have four units currently running the open version of the system, and that has never been an issue. Basically the btu of the 40 gal water heaters is well above the radiance of the heat system, so the recovery is not noticeable.

@h@HomerJSmith thanks but I know all of that about how to construct the system. I've just found that making a question.too long and complicated  leads to fewer answers here, and thought that 'safer'and 'exchanger' would show that I know this stuff.

PC7060

@Jells - so do you use a mixing valve or does the heating loop get the full 100-130F temperature water from tank if there is no ongoing call for DHW?

Jells

PC7060 said:

@Jells - so do you use a mixing valve or does the heating loop get the full 100-130F temperature water from tank if there is no ongoing call for DHW?

I'm heating this time with kickspace heaters, others have traditional baseboard, so I want to run as hot as I can, close to 140. I put a mixing valve on the DHW out. I posted here because of the similarities to radiant systems.

All DHW heaters should be 140 with a mixer to eliminate the Legionella risk. I've tried discussing this with local plumbers and suppliers, all of them poo poo the whole thing and still recommend circulating potable water. TBH, I haven't had any issues in the many years I've had them, but why not do better if you can? Another $500 in gear and some labor doesn't make much difference in the long run.