hondaracer2oo4,
I think you missed the point totally, your boiler don't cool down, it is always hot in the firebox, and the steel in the firebox is at that temp. When you pull heat out of the water the less water means the whole system will cool down faster if you have a thin firebox and the boiler will have to be started up with the draft. The more water in the boiler the longer it takes to draw down the temp. I've had my boiler for 15 years and it has 400 gals. of water in it. I only need to fill it once a day. I'm heating over 5,000 sq.ft. with the shop which never gets below 55 degrees at night where I set it. The house is 75 degrees night and day. The hot coals in the firebox keep the steel hot all the time. I know of owb owners that have thin steel and a small amount of water and they are running all the time, I know this because I can tell when a boiler is running by looking at the smoke coming out or it is shut down, being up to the temp.