Over the last couple of years I've been decreasing the gallons-per-hour figure of the nozzles I install in my furnace. For those that don't know, your typical residential oil burner runs its pump at a relatively constant 100 PSI and it's up to the nozzle size to regulate just how much oil [and thus how much flame] gets shot into the firebox. The original that came with the place was 0.75 gph with a 60 degree hollow pattern [or "60A" in nozzle parlance], which made a *lot* of flame and splashed a lot of it against the far wall of the relatively small refractory area in the heat-exchanger can. I dropped that to a .65 gph 70 degree and that seemed much more appropriate; the flame was more centered in the firebox and there was just less of it, and I could stop down the air somewhat to still have good combustion. In the interest of saving even more fuel, last year I ran the smallest nozzle I could find -- 0.5 gph, 80 degrees. This made an even smaller and bushier flame right in the middle of the firebox that barely touched the refractory walls. The air damper could stop down to almost closed [there's still some inlet leakage from other holes in the burner housing, so it wasn't a total cutoff] and I knew the volume of air [and thus heat] going up the stack was a lot less. It seemed to take a little longer to get the big ol' can hot enough to kick on the fan, but I figured that was fine -- akin to accelerating slowly to save fuel when driving, etc. But this year I noticed, or rather confirmed from a mild suspicion last year when sticking my head out the door and sniffing the air after the furnace started up, that it was emitting quite a bit more visible smoke than it should -- puffing out of the chimney and swirling around in the nearby trees. Yech. The flame in the box looked fine, but what I suspect might have been going on is that the best combustion adjustment I could do on that rig had the air stopped down so much it wasn't getting good flow *past* the nozzle down the blast tube, leaving some amount of oil unburnt in the exhaust anyway. Very frugal on oil, yes -- between this and keep the house temp fairly low and various other behavioral mods I got through last winter on less than 100 gallons -- but its actual efficiency was clearly all over the place and probably annoying the neighbors every time this ol' monster cranked up. And now the nozzle had a season of wear on it already. I just went back to a new 0.65 nozzle this afternoon, fired 'er up and ran outside to eyeball the chimney -- no smoke at all, even from a relatively cold startup. So I guess there's a lower limit on how far you can downsize a nozzle, if the design of the burner gun still wants to push X amount of air through the system when it's running. Although this thing is so old it's unclear there was ever really a "design" process behind its creation, other than messing around with casting shapes until it worked acceptably. I think the biggest fuel-saving factor is lowering the thermal gradient, i.e. keeping the house [and its contents, which can be a huge thermal-mass flywheel] as close to 50 degrees as tolerable and bumping up actual occupied spaces with oil-filled electrics set on "low". Been doing that for a few years now, and nozzle-futzing aside the yearly bills speak for themselves. If I can keep the nozzle upsize as the only thing I changed this year, I'll have a better idea of which factors carry more weight. Oh, and you can get lots of self-maintenance burner parts at F W Webb. What I haven't done yet is replace the supply pipe, which is one of the now-illegal ones buried in the slab ... was reading up on stuff this morning and the right answer is probably an overhead line and a neat widget called a Tigerloop, which is a de-aerator that mounts right near the burner and makes the system far less vulnerable to small air leaks or foamed oil. [look up westwoodproducts.com] This sort of simulates a two-pipe feed system without the disadvantages thereof. I now know what a "bypass plug" is and where it's located on some of the more common pump types. A new oil tank might be prudent to add at the same time; the Roth dual-wall types are intriguing especially since they have floating pickups instead of the tank-bottom one I've got now that *has* had one or two water problems in the past. _H*