give you an exact heat loss on your home without knowing anything about it's age, construction, r-values, u-factors etc..
Ashrae winter design temp for Philly is 14. Personally, I would design for a 70 indoor temp at 0 outside with a 15 mph wind.
I can tell you that 60k sounds a little low unless home was built with newer style construction, r19 ext insul and decent windows (better windows if they are large)or upgrade a great deal if an older home. Heat loss programs are JIJO, so don't make too many over assumptions when inputting info. A good rule of thumb that I have use successfully is this:
well insulated, modern home- 18-25 btu's/sq ft
avg to poorly insulated- 25-35 btu's/sq ft
poorly to not insulated- 35-45 btu's/sq ft
barn- 45-60 btu's/sq ft
your home at 60k rings out to 25/ft based on your info. remember the net output of the boiler needs to meet or slightly exceed the heat loss, not the input
curious about the answer to another post- does this boiler need to make domestic hot water such as with tankless coil?
ok, sounds like you've made some improvements to the house. not telling you 60k is not enough- I assumed your house was built in the 50's or earlier by the boiler age and have never seen exterior wall insul in a house that was built then ,unless it was gutted later and added. good luck
I've decided on a boiler: 103 MBTUH input. And, I like the idea of an outdoor reset. Let's just leave that alone for a little while. Of course, if there are any major objections, please reply.
Now, onto circulators. Several people have recommended 1 circ per zone. Sounds like a good idea. What exactly is "head-feet"?
Dof3 suggested, "If you are planning on replacing the boiler, why don't you use a P/S piping system. Then put a mixing valve in the zones that are too hot."
I'm not exactly sure what is meant by a Preliminary/Secondary system. Is that the same as what someone described to me as a "two-pipe system", where there is 1 loop for each zone, and the radiators are Teed-off of it?