I would like to first thank everyone who contributes to this forum - I have been lurking here for quite a while and have learned a lot. I am currently finishing laying out a panel to convert my current open loop heating system to a closed loop system isolated with a heat exchanger. Based on all the reading I have done, I am pretty comfortable with my design but had a few remaining questions: 1) I wanted to use unions to plumb in the heat exchanger, in case it ever needed to be taken out for servicing/replacement. My plumbing supply store only had dielectric unions which I think will be OK, but I was curious to know what is typically used to plumb in a heat exchanger (3/4" male threads). 2) I have a schraeder valve that I will plumb in with some pex prior to commissioning the system to pressure test it with air. I have a Callefi Air Separator - can I close that off so the system will hold pressure for testing? I'm not 100% how these guys work and whether they would just bleed out the air I will pump into the system. 3) What is typically used for wells to tee in tridicators/thermometers? My plumbing supply store didn't have anything off the shelf, so I think I am going to use a copper tee with a length of pipe to accommodate the stem, the reduce it to 1/2" (thermometer) or 1/4" (tridicator) using one or more threaded couplings. 4) I will be using an Axiom MF200 system to maintain system pressure. At present I am not planning on using glycol on the infloor side, but if I do, how do people get the glycol/water mix in? I have read that some people will use the MF200 to feed the entire system - I'm not sure it is designed to do that. Presumably I would need to use compressed air to blow out the water current in the system, measure the volume and then either use the MF200 or another pump to pump in a glycol/water mix? (As stated, this is for future consideration - currently I am going to use a Webstone purge/fill tee to fill the system with water initially.) Thanks!! (Sorry for the big block of text, I wasn't able to insert line breaks into this message).

1. Unions are a good idea with the heatex, but of all the possible system components, they are on the lower end of the failure scale IMO. So if you don't use them, you probably won't ever have need to kick yourself for not doing so IT probably wouldn't be that much of a kick anyway as it sounds like you can do your own work...

2. Your air separator should have a threaded port on it to allow the air to escape. That will have to be capped to allow an air pressure test.

3. That should work to get the sensor stem into the flow. Electric contact thermal sensors can also work pretty well attached to the outside of copper pipe using heat sync compound and then covering/insulating the sensor from outside air. This is better near fittings where flow turbulence will keep the wall temp closer to average fluid temp at that point. I have seen electric test sensors put in place with no more than heat sync compound and a piece of foam tube pipe insulation to hold them in place.

4. What is the volume of your system? If you know the system volume, then adding the correct ammount of Propolene Glycol to the Axiom to be injected.  Then it should be as simple as draining out that same ammount of water and allowing the Axiom to makup for that lost water with PG.  This should work as long as the drain point isn't immediately downstream from the Axiom. An isolation valve between the Axiom feed point and the drain point would be ideal as this would force the injected glycol into the rest of the system as the water is drained off.  This would also be great for charging/purging the system of air to promote flow thru the entire system.
 
I don't see why the Axiom wouldn't be able to fill the system. It is basically just a 24V RV or AG sprayer diaphram pump in a fancy package. An inexpensive sump pump with a garden hose fitting in a barrel with the garden hose fitting connected to a drain valve/port should also do it. A washing machine hose should work well for this. Again an isolation valve between the fill point and the drain point would be great.  Then as you get close to the complete fill you can run a hose back into the feed bucket(or Axiom) from the drain port.  The fluid will recirc into the bucket and any air bubbles will be allowed to escape in the bucket as the water circulates... 

Good Luck

OH, and this appears to be an older forum engine, so I think depending on what browser you are using to access the forum, sometimes it reverts to using HTML formatting.  In HTML a break or return is accomplished by typing <  BR  > but as one word, with no spaces between the greater/less than symbols and the BR.  I can't type it that way as the forum engine reads it as a break and in the submitted posted text it disappears and it puts a return/break in my sentence:)  Using that combination of characters will allow you to break up your single big block into paragraphs...

Thank you very much for your reply. I am backing away from the idea of using unions now. I've read a fair number of compliants about leaking dielectric unions and other unions (copper) seem to be pretty finicky.



I have narrowed my course of action down to either plumbing the HX in with PEX to allow for relatively easy future servicing or to just solder it in. The only thing I don't like about soldering it is that my experience with threaded connections (male NPT on the HX) is that every so often you'll get a leak and then I'd need to unsolder, try to fix the leak and resolder. That being said, I'm not sure the PEX route will look nearly as good.

Well it is all going to be buried in insulation anyway isn't it?

I will hopefully soon be in a similar situation, incorporating a heatex to import heat from a mass storage tank. Street L's off of the heatex and then NPT to pex adapters to the L's. Sharkbite fittings would make it quick detatch...