Old House Retrofit

browndogtripper

We have a home built in 1900 in Tacoma, WA. It is 1500 square feet 2 story Victorian with tall ceilings and three bedrooms upstairs. We don't mind the bedrooms being cool. It has a full height basement but because of the pony walls and moisture issues it will never be heated. Our heating system now is a 50 year old gas furnace with essentially one vent in the center of the main floor. The 40 gallon water heater is leaking and ready to give up. The old fir floors are in poor shape. I'm looking at the Laars Combi Core Water Heater with Heating Coil. It seems I could run one circuit to heat domestic and another circuit to either radiant pex on the main floor only and a radiator in the upstairs bath, or radiators on the main floor and the upstairs bathroom. It seems that I would only require one zone, one thermostat, one pump, and an expansion tank. How would this perform? Am I missing something.

Ironman

Yes, A Heat Loss Calculation

And putting radiant on just the first floor + a bathroom may not give enough btu's to heat the entire house. Just because your present furnace only emitted heat to the first floor doesn't mean you only need radiant on the first floor. The gas furnace may have had a higher output than what a radiant floor will have. You need to do an accurate heat loss.