gravity hot water system exspandsion

jim_160

i have a job that has gravity hot water. it has 3" and 4" mains around the perimeter of house. one supply ,one return. 1" supply and return go to cast iron radiators off the mains. it works fine with a horizontal tank for expasion in basement.

Jim_166

gravity hot water system exspansion

I have a customer that has a gravity fed hot water system with an open exspansion tank in the attic. They would like to cap off the tank in the attic and install an exspansion tank in the basement. anything special I should know before I take this on. The system only gets to 10psi before the tank over flows.Any help would be appreciated
Thank, You
Jim

Mike T., Swampeast MO

Unless you convert to forced flow with a circulator, you have to leave the open expansion tank in the attic. It is an integral part of the system that helps ensure proper circulation (and safety).

Gravity systems are open--they do not operate under pressure. You see pressure at the boiler only because of the weight of the water above. At the top (in the expansion tank) pressure is zero.

You'll find an altitude gauge on most gravity systems. It has two arrow--one fixed (usually red) and one that moves. Set the fixed arrow to the proper altitude that keep the expansion tank about half full with the system cold. Fill as necessary to keep the moving arrow right over the top of the fixed arrow.

There used to be some components made that allowed a closed (compression) tank in the basement, but they're long, long gone.