how to figure out water fill pressure

Jerry Boulanger_2

that explains required cold fill static pressure.

http://www.axiomind.com/downloads/coldfill.pdf

Dave_61

how to figure fill pressure

Our boiler currently runs at about 20 pis with a 50/50 glycol water mix. The lowest pressure allowable is 12 psi.
What should we set the autofill valve at and how would I know what it is set to? Would I just watch the boiler pressure gauge to see what the pressure is when the water stops flowing?
Thanks.
John

Empire_2

On a cold fill

You are correct. 1 psi will raise water 2.34 feet roughly.
12 psi is the factory setting and usually ok for most residential 2 story dwellings. I would consult a glycol chart though because I'll bet the glycol /water mixture has a different spacific weight that just water alone. The guy's in here are very sharp and you will get your definitive answer.

John_96

I went to Watts

website and found a calculation....the height in our house from the fill valve to the top of the uppermost air handler is about 37 feet (3 stories).
So, by their calculation, it should be 37 * .43 + 3= 19 psi.
That should also be what our expansion tank precharge is set at?

JimGPE_17

Yep.

Empire_2

Just so I know

Did the glycol mix make a difference? Was there a chart?

Brad White_9

The difference in density is

insignificant. As with water or any fluid it does vary with temperature. The attached .pdf is regarding Dowtherm. Being miscible with water, it would seem that the minor density differences would cancel each other out.

John_96

I spoke with someone at Amtrol,

and they also agreed that glycol will not change fill pressure as opposed to just water.

EBEBRATT-Ed

Expansion tank air pressure with the tank isolated from any water pressure should be set to the same pressure as the fill valve.

ED

Empire_2

Thanx Brad

I wasen't sure that there was a diff., but I have looked @ the chart and it does make sense. I appreciate an answer when I am not sure or have other thoughts that in affect may be incorrect, but that's why "The Wall" is so great . After all if we knew everything, we would surely not be "Only Human". Again thanx.......Mike T.

[Deleted User]

How come...

you have Aunty Freize in your system? IF it IS necessary, I'd not leave the make up on or Uncle Inadvertant Dillution may show his ugly face and mess up EVERYTHING...

If you wisely chose to shut off the make up, make sure you install a low pressure/low water cut off to avoid dry firing the boiler.

If glycolization is not necessary, get rid of it and avoid future service troubles.

ME