Can I change my oil gun to a gas gun in my boiler ,I have a Weil McLain gold series

I believe this to be a weil mclain gold series boiler..
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You can change to a gas burner, but the dynamics of gas versus oil as far as the boiler's construction is concerned, means that the gas will NOT be as efficient as if you had a designated gas boiler.

I'm with HJ...you'll be lucky to see 70% eff if that.They saved $ when oil was $3.75 a gallon, With the low price of heating fuel it makes no scene.

in the old days, we would stuff a couple of fire bricks in the flue passage to increase efficiency.

You'll lose a small amount of heat due to the btu carrying capacity of the 2 different fuels. You won't lose any efficiency. Your chimney will probably need to be lined with a stainless liner. That adds to the cost of conversion. Most likely, your boiler is over-sized, so I wouldn't worry about the loss of btus. If your chimney is not lined, I'd consider losing the oil-fired boiler and put a mod/con in its place. If sized correctly and installed correctly, you can save 30% off your fuel bill. Even with oil prices down. If you do a heat loss calculation of you house, you'll probably be amazed at how little heat it requires. Most people are.

if converting to gas a liner is a good idea but stainless is not needed. the inexpensive aluminum liners are fine for gas..

What about the acidic residue left in the chimney from the oil, packy?

i didn't know that was a problem ? i'm not saying it isn't, just that i've never heard or addressed it ??

When oil prices were sky high, I had a lot of discussions about converting. All the contractors stressed cleaning the boiler thoroughly and that you must use a stainless liner. The residue in the flue will not play nice with aluminum.

If the efficiency was higher (near Condensing) it would justify using SS...Aluminum will be fine.Lets face it,the cost to do this right with the Gas gun will get so close to a new Con/Mod (with Gov-rebates) it gets a little silly doesn't it.

Have you seen the existing boiler in order to make that assessment?

Cost of materials,running a gas line,lining the chimney,Permits...The labor of a Technician who not only owns but knows how to use a combustion analyzer all for what,80-82% eff, a few grand more and you have 96% out of the box and a brand new Heater not to mention more basement floor space.

So as not to mislead anyone unintentionally, and I agree with the mod/con suggestion. You can always get better efficiency with a mod/con. Your chances of getting that rated 96% in a retro-fit situation are probably slim. It relies on the house being over-radiated. If you can't heat the house with a low enough temperature water, to have the return come back cool enough for the boiler to condense, you don't get the efficiency.

I hear ya Paul but I believe the days of heating the chimney to 400 degrees are over...The day's of chimneys are over.