Unpressurized system question

[Jim K in PA]

I am still in the design phase (won't have my GARN until August) and have a question. This is a simple hydrodynamic question about head and drainback.

My GARN will be installed about 80 feet away from my house on a slab behind my garage. I plan to depressurize my oil fired HWBB furnace and circulate the HW from the GARN through the furnace. My furnace is in the basement, about 5 feet below grade at the house. My GARN will sit about 18" above the house grade. The furnace has 4 zones, two up and two down. The upstairs loop goes no higher than about 8" above floor height, or about 8'-8" above grade at the house. The top of the GARN is about 6' high, with the water at some point below that - let's assume 5'. End result, the upstairs loop will be approximately: 8'-8" minus 1'-6" minus 5' = 2'-2" above the highest static level of the water in the GARN, +/- 6 inches or so.

After hookups are done, in order to keep the water in the upstairs loop from draining back into the GARN, I must do the following:

1. Fill/bleed the GARN and the system to it's static level
2. Pressure fill/bleed the zones in the house after isolating the GARN via valving
3. Depressurize the system by shutting off pressurized supply and opening GARN isolation valves
4. Finally - as long as there is no way for air to enter the system, the upper zones should remain full and air free, with no drain
back to the GARN as long as there is no way for makeup air to get into the upper zones.

Do have this right?

 

[deerefanatic]

yep, make sure your joints are tight! I'd suggest sweat soldering as much of that space that's above the garn as possible to avoid any future problems..... No valves or air bleeds up there either.. (Yes, even shut off valves can allow air to bleed around the packing gland.....)

 

[Jim K in PA]

yep, make sure your joints are tight! I'd suggest sweat soldering as much of that space that's above the garn as possible to avoid any future problems..... No valves or air bleeds up there either.. (Yes, even shut off valves can allow air to bleed around the packing gland.....)

Thanks DF. I have no valves, but there are two air bleeds on a couple of elbows. However, they are the simple cap & gasket type, so if any negative pressure occurs in the circuit, they will pull tighter. It is all sweated copper. The only time drainback could occure would be while the ZV is open.