Water leaving the system

Snowmelt

Have a question for you guys that are good with your definitions? I know that you know water evaporates from your heating system because it’s technically a closed system and you have makeup water yada yada yada. My one good friend who is actually a chemist by trade. Understands the theory, But I couldn’t explain in some sort of way what physically goes on.
Can someone explain how it leaves the pipe and air will go in if no pressure on the system.

mattmia2

What kind of system? Closed hot water systems only lose water if there is a leak. Steam systems evaporate some water in to the air that fills the system when it is cooling and the steam has condensed to water, the next time it heats the steam forces that air out which has some water vapor in it.

Big Ed_4

In a perfect system , no water is loss ...

Snowmelt

Ok let me rephrase the question, if you take all the air out of a system, and let’s just hypothetically say you let the system run for two years off and on and you monitor the incoming water ( makeup water) you have it set for minimum of 15 psi.
Your telling me if I shut the fill valve it should never ask for water and pressure shouldn’t go down accept in possibly temp fluctuation like Air-conditioning?

mattmia2

Yes.

Tinman

As as mentioned above, water is only leaving the system by way of a leak or during a manual purge. Once all the air is out and the system is tight, pressure will stay relatively the same. My system was filled two years ago, the make-up water is off, and the pressure hasn’t budged. I have a operating and maintained LWCO. 

GroundUp

A closed hydronic system will never need makeup water unless there is a leak. I install 50+ hydromic systems per year and I can count on 1 hand the amount of times any of them have needed any makeup water- every time was due to a leak. Quite a few that were installed upwards of 15 years ago that I still manage, are still holding the original 12 psi charge. I know this, because I have never once installed an auto feeder.

PC7060

mattmia2 said:

Yes.

What Matt said.  I leave my fill valve off on my hydronics heating system. Only need to turn on for few seconds after flushing the DirtMag. 

hot_rod

air doesn't enter but O2 at a molecular level can and does. That is why O2 barrier tube is used.
But even barrier tube allows some O2 into a closed, pressurized system. It is temperature related. the amount of O2 that can enter. The industry has a number for allowable O2 ingress, on barrier pex tube. It is included in all the listing numbers you see on the tube.