Originally Posted by raymr

I worked out a spread sheet and none of the options pay for themselves until 3-5 years down the road. I figured in oil prices climbing from $4 to $5, and gas increasing by 20% each year. The most expensive after 3 years is still the condensing gas boiler. In my case I have to consider the $700 loss of the oil in the tank (you can barely give the stuff away around here) and $1500 to have the tank cut up, cleaned, and removed. I liked the idea of keeping both oil and gas systems, but I don't have the room.

The cheapest solution is switching to a retention flame burner on the existing boiler. I might even be able to do this myself. Next cheapest overall is the regular 83% efficiency gas boiler. As a rule, you pay a steep price up front for the best efficiency. Of course my calculations could all mean squat if fuel prices go on another wild roller coaster ride.