Secondary loop on closed loop hydro heating question

[DR Buck]

I'm hooking up a secondary loop to my Central Boiler outdoor furnace through a plate heat exchanger.  The secondary loop will have glycol in it so that I do not have to circulate it all the time.  Only when I need heat from it.  I will be using the standard TACO pump to circulate when heat is needed.   Questions are:

Do I need to pressurize the secondary loop?  I don't think so, but not sure.

If it is pressurized, how do I put the glycol in?

If not pressurized, can I just use a small non-pressure bladder expansion tank to fill the loop and and allow for liquid expansion? 

Should the expansion tank be vented if the loop is not pressurized?   I'm thinking something like a small (couple gallon) hydraulic tank.

[JSNH]

I added a plate heat exchanger with glycol. I put a small 5 gal electric water heater on the line just before the pump. The drain line of the tank I ran to a tee before the pump. The hot out on the top I put a valve on it the cold in I plugged. I opened the valve and added the glycol. I then put a shrader valve on the valve and added 5psi of air. Turned on the circulator and had no problem getting the glycol in the system. Depending on your piping length you may need to fill the tank more than once.

JSNH

[Holmes]

 Hi Dr_ Buck  You need an expansion tank if it a closed loop. You can have an open loop with an open standpipe as long as it is a few feet higher than the highest piping of that zone and you could fill the system thru the stand pipe. Some old heating systems were open  to the atmosphere but the stand pipes ran up to the attic. You could do the stand pipe , fill the system then screw a small #15 or 30 expansion tank in the top of the stand pipe. That may be the easiest way to do it. Holmes