Charlie Z wrote:So, do the auxilary oil burners work ok, or are they too inefficient for vacation or the corners of the coal season?
Yanche, I know that you did not think much of them. I'd like to save a stack, if I can.
I guess I didn't make my point about efficiency very well. Let's try again. All but the most modern oil fired boiler have a combustion efficiency around 84%. That means 84% of the approximately 140,000 Btu in a gallon of #2 fuel oil gets converted to heat. You also have equipment efficiency, how well the appliance converts that hot flame to hot water. When the boiler is operating at the max firing rate the flame to water heat exchanger is doing the best it can. It's at the max design point. All the little tits on the casting are collecting the flame heat and transferring it to the boiler water. The manufacture rates the boiler at a certain Btu and sets the corresponding nozzle size. If you reduce the nozzle size the boiler operating efficiency will go up. The heat exchanger stayed the same but it now works better. More tits on the casting than are really needed to get the job done. Combustion efficiency stays the same 84%. Can't change that it's largely just combustion physics/chemistry. So if you have an oil burner sized for heating your house AND you made no changes AND the oil burner is now used only to heat hot water in the summer because you now heat with coal, it's to large. It will operate inefficiently, short cycle, etc. Combustion efficiency (84%) stays the same operating efficiency goes down. If I now change the nozzle to a smaller size operating efficiency will now go up. The boiler water Btu production is more closely matched to domestic how water needs. BUT in winter, if your coal fire goes out you want some backup oil heat. It will work with the same 84% combustion efficiency and a better than manufactures rated operating efficient. BUT, you can't get the original Btu's out of it because you reduced the firing rate. If all you want in winter is to keep the house from freezing it will work. If you want your cake and eat it too, change the oil burner nozzle seasonally. Small size in summer, standard larger size in winter.
Charlie Z. Want to save a chimney stack put the oil burner on a direct vent system. Use the clay lined chimney for coal.