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How to calculate recovery rate for indirect DHW

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Boon
Boon Member Posts: 260
in THE MAIN WALL
Hi. I'm trying to calculate the actual recovery rate for an indirect DHW given my boiler size. I think I'm missing something.

Cold water 40°F
Target 130°
∆T = 90°
90° * 8.34 = 750 BTU/gal
If the boiler is 55000 operating at 87% then I'm taking 47,850 BTU/hr ÷ 750BTU/gal = 63.8 gal/hour

But 63.8 gal/hour assumes that 100% of the 47850 is being transferred to the DHW and that can't be true. And I think the flow rate [between the indirect and the boiler] matters, too, but I don't know how to account for that.

Am I on the right track here?
DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.

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