Help Sizing Steam/ HW combo

Jack W.

We just went into contract on a oil fired single pipe steam house on Long Island that needs a new water heater (current is stand alone). We are not local (my company transferred me) and I brought in a local guy to give us his opinion during the inspection. He suggested just adding a Phase III indirect to my current boiler, and I am interested in knowing if you guys think the system can handle it, or I would be better off with a new boiler.

House is 1949, some blown insulation, 2 story. Current boiler is Peerless ECT-04 1.25 with a Riello burner from 1994. From the Peerless website, I found:

Gross output=151
Steam Sq. Ft=471
Steam MBH=113

Main steam system is 55 ft of 2 1/2" mains feeding 13 1/2 linear ft. of 5 1/4" copper fin and 32 sections of Burnham Radiant Cast Iron (80" w x 20" h). If I understand correctly (Using the Burnham Heating Help Guide) that equals 164.1 sq. ft. of copper fin (based on the size of the cabinets) and 72 sq. ft. of cast iron. The selling homeowner removed one large (@53 in.) copper fin steam rad from the second floor during a remodel when the cast iron went in.

The Boiler has a 10 GPM max tankless water heater that is running 2 zones of HW heat. Zone 1 is a family room converted from a screen porch, 37 Linear ft. of older 7 1/2” high cast iron Basray. Zone 2 is a bedroom over an unheated garage with 25 sections of Burnham cast iron, 45 sq. ft. according to Burnham. Zones are currently set at 150 degrees, and current owner claims no heating problems even on the coldest night.

All rads are recessed into walls.

Sorry for the long setup, but the question is this: Would it be smart to follow the contractors advice and add an indirect (family of 4, 2 toddlers, 2 showers, 1 reg. tub) to the second tankless heater on the front of the boiler or should I replace this whole setup with something else because it is too big/ too small/ put together wrong? We are not looking to spend $ unnecessarily, but want to get this rigt now and not worry about it while trying to get our lives together in a new city.

Thanks.

Jack W.

Do I have this right?

Attempting to answer my own question based on all the info in the library here, if I did my math right I have 236 sq. ft. of radiation in the house, and a boiler that produces 471 sq. ft., so it is 50% oversized, with a pickup factor of 155 sq ft. Is that right?

Is that 155 sq. ft. pickup enough or more than enough to run the 2 HW baseboard zones off the tankless coil, and would I be OK adding a 66 gal. Indirect HW tank? Thanks.