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sizing indirect for solar post-heat
Have a solar DHW system that needs boiler supplement in winter. Typical worst case lowest tank temps around 75F. Average temp rise required around 40-50F.
System is piped with a 3-way valve that allows seasonal SDHW only, and winter SDHW output to boiler-fired indirect (a tired old poor performer).
Existing boiler is 84k output with DHW priority control.
Question is whether to go with smallish 20 gal indirect (e.g., SSU-20) and shoot for basically continuous hot flow capability assuming fairly low temp rise, or go with larger indirect that does more 'standard' dump-and-recover service.