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Gravity Conversion in Mid-America

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Buzz G.
Buzz G. Member Posts: 61
Biggest problem is that in Oklahoma, residential heating is not often by hot water and CI radiators. Thus finding someone with experience is difficult-so let me ask several questions after identifying my original setup.
100 yr old boiler, coal converted to NG sometime in mid century. I measured gas flow at meter several times and found it to be 3 cf/min or 180,000 BTU/hour. Assuming that it is working at maximum efficiency of 70% (dream on), this would be 126,000 BTU. I have 956 sq ft of radiators (CI) which should be able to emit 180,000 BTU, if it were steam or very hot water (the system has Honeywell Hg device described nicely by Holohan for raising the potential temp of the hot water) so that fits with their choice of gas burner in the first conversion.
We have insulated (some) and added storm windows and over past 37 years have been warm and the water in the boiler usually less than 140 degrees (recall once getting almost 160 degrees)-not sure what return temp was. So probably doing some condensing on its own and damaging the chimney which was not lined.
The man who sells the boilers says I need 200+ MBTU- think I need only 155,000 BTU to do the job and to get advantage of the system. He sells Knight and W-M. Also I had some questions over the size of expansion tank-old open one in attic 28 gal and so measured the volume of the system (rads + 3"pipes) as about 170 gallons. How big exp tank do I need? Which Mod-con boiler size and make? How do I convince dealer? I have figured the heat loss two different ways (Slantfin's and another) and got about 151,000 to 167,000, the second being based on more generalities. Also not sure whether the Honeywell Unique valves cause any problem with forced circulation.
Also do you know of any installer in the Tulsa area? Sorry for so many separate questions.

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