Hello all, This is my first post here. I am planning on building an OWB and want to use a gravity feed to circulate the water. My OWB design will be based on a return tube boiler and opperate at atmosphere pressure. The shell is a stainless tank 24" X 72" laying horizonal with several flues running between the heads. The firebox is under one end of the tank( the front). The gasses will travel back under the tank up the rear head, thru the flues, out the front head and up a stack. This will give me a hot fire on the outside of the water tank with a lot of heating surface. I can locate the OWB about 25' from the house and about 15' feet below the main floor. I have plenty of 1 1/4" copper pipe to run for lines. Can I expect to circulate the water with no pump using radiators for heat exchange? The hope is to have heat with no power.