How do you figure static fill pressure for this system?

Rocky_2

the tank would be at 37 psi. If I then added an additional 12 psi fill pressure at the boiler, the tank would see 49 psi while the boiler only sees 12? Am I thinking right? I really appreciate the info, Steamhead. This job will be a little different. Not only do I have radiant in the garage and house but there will be a melt system for outside. Not snowmelt, but septic-melt! Due to ground particulars, his leach field is going to be really shallow and right in the path of all snowmobile and car traffic so frost will go deep due to no snowpack insulation. He wants me to run a zone of radiant above his leach field about 4 feet down and then insulate over the top of it with blue board. Will use snowmelt sensors embedded in the ground in leach field to turn on the "septic-melt" system. Hopefully will keep his leach field thawed and useable all year round. The things we get into!
Thanks for the info,
Rocky

Rocky_2

New vacation home construction

on a lake. Detached garage is up on the road, while house is down the hill. The garage sits approx 85 vertical feet above house, and approx 200 feet away. House and garage is all radiant. Will have an 80 gallon buffer tank in house as radiant source. Want to put boiler in garage and run Ecoflex Thermotwin down to house to the buffer tank. Will the elevation change between the boiler and buffer tank cause problems? I know of the "Ferris Wheel" effect, what goes down is balanced by what comes up, but won't I still have to raise the static fill pressure of the boiler? And if so, how do I figure how much? Just want to make sure I can get my water from the garage to the buffer tank with plenty of oomph without going negative at the boiler and sucking in air from all the vents. Thanks for all the great info in advance,
Rocky

Steamhead (in transit)

Since the boiler is the high point

the highest pressure will be in the house. Since 1 PSI=2.307 feet of water, you'd have just under 37 pounds at the house just from the height. I'd figure on another 5-10 PSI to keep enough pressure in the system so air would not collect. So the buffer tank and any other system components in the house would have to be able to handle at least 45-50 pounds of pressure.

Steamhead (in transit)

That's right

49 pounds at the tank when the boiler is at 12.

You'll want to isolate the septic-melt with some sort of heat exchanger. This will provide an additional level of protection for the potable water, in addition to the usual backflow preventer on the boiler water feed line. It will also ensure that if the septic-melt tubing gets damaged, it won't let the water out of the rest of the system. I would do this even if Code didn't require it on your job.

A good friend of mine tells me that leach fields work by evaporation upward, so the blue board insulation may not be such a good idea. But you could run antifreeze in the septic-melt loop- the aforementioned heat exchanger would isolate it from the rest of the system. Same goes for the loop between the boiler and the house- that could have antifreeze in it if needed.

Oh yes- you are using a sealed-combustion boiler in that garage, right? Don't want any gasoline vapor sucked into that burner!

Steve Paul

MULTIPLE PRESSURES`

To avoid super high pressures on the lower system components, how about using a heat exchanger for the buffer tank to be heated from a submerged coil in the boiler. That way you can safely maintain 45-50 psi in the coil and heat exchanger but not have a great pressure on the boiler, the buffer tank or any of the attached heating systems.It would require 3 seperate pressure regulators, 1- for the 45-50psi to the coil and heat exchanger. 1- for the buffer tank and lower systems (set at10-12psi) and 1- for the upper boiler (set at 10-12psi). The boiler water feed regulator can connect to the coil/heat exchanger lines.