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Posted by HeatPro on January 08, 2006 at 01:29:45:
In Reply to: advice for ancient boiler posted by Brendan on January 07, 2006 at 23:33:12:
Old boilers were made for solid fuel, so they have wide passages meant to pass ash. For that reason they were 50% efficient at best. Converting them to gas lowered them to about 35%, as there is no radiation from a gas fire and most of the heat absorpdtion takes place in the flue passages, whereas solid fuel boilers make use of radiation in the fire chamber and wet legs or wet base. In the 1970's gas boilers increased in efficiency from about 65% to 75% due to the addition of a flue damper, which previous boilers didn't have.
You wouldn't be able to touch a flue pipe in a modern non-condensing boiler either as the flue is usually over 250F.
Most boilers today come from the factory at better than 84% AFUE efficiency, so any modern boiler you get would save half your fuel costs. Thre is little you can do to make your old boiler much more efficient, other than putting a stack damper on it to stop letting it push the heat up the chimney while the burner isn't on. Pick the boiler caried by the local plummbing suppliers as they carry the boilers because the plumbers respect and use them and can get parts there for them.
Insulate the house to as close to modern standards, then replace the boiler with a new one, as insulating your house will cut your fuel use by 2/3 rd and after insulating your house you will need a smaller boiler. Do it the other way around and you get a boiler too big for your insulated house. Or get three boilers that equal the same input as the one you have now, then after insulating the house throw two of them away.