I have an oil burning furnace with hot water baseboards. How many pressure release valves do I need? On the first floor there is one in each room on the side where the pipes run back under the floor. On the second floor, there are only two. One is very low to the floor in a back closet, the other is in a closet but this one...the pipes do an upside down U shape (4 - 90 degree turns) and there is a release valve at the top, about 12" off the floor. Interestingly, there is no release valve at the furnace or in the basement. I am getting air in the pipes. Could all of these valves be the issue? Do I really have to bleed each of them? Uggg!!!