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geothermal with cast iron radiators
(searching the wall, most of the discussion on this subject seems to be a few years old... so I'll post my question as follows)
Are there ways to use geothermal with old cast iron radiators?
I live in southeastern PA and have a circa 1888 brick home with cast iron radiators that I don't want to give up (for many reasons, including quality of heat, historical appropriateness, etc). We use an oil-fired Bethlehem Dynatherm boiller installed in 1944 that is also used year-round for hot water - no boilermate etc.) I have been doing lay research on geothermal for several years, but it has seemed that it would not be efficient for use with cast iron radiators. Is this still the case? Please don't just say "no". I'd like to find out if there is ANY kind of system that could be developed, perhaps costing more and providing less efficiency that "typical" geothermal, that would allow me to keep my radiators and still be cheaper to operate than my current (and future) oil bills? I am told that geothermal systems usually max at 130F and cast iron radiators need 180F to be useful. Thats understandable to me, but I'm wondering if there are alternate geothermal systems that use some auxiliary technology to boost to 180F that might still be more efficient than my oil-fired boiler.
Please don't suggest just switching to a new oil burner or to a gas burner... I have other situational issues that won't allow me to easily do that. My current 4" flue is too small for new oil burners which I think require min 8" flue. I would have issues with condensation in the brick chimney. I don't have anyplace I could run a new chimney without destroying the historic exterior. Similarly, I don't have a good place I could vent a direct-vent gas burner, due to wraparound porch, etc. I was optimistic that maybe by using Geothermal with my existing radiant system, at least I would only need to run underground piping (I do have yard space for that.) There are also the tax credits as an incentive for the capital expense.