Dana - by "how much radiation", I assume you mean how many feet of base board. The four zones are 60', 38', 55' and 40'.
Tom - What do you mean by "bug two zones on one relay"
Here's the fundamental system design problem that crops up when it's cut up into so many zones:
The DOE output of the
Sentry S-120 boiler is 101,000 BTU/hr.
Fin tube
baseboard puts out about 600 BTU/hr per running foot when operating at an average water temp of 180-190F.
The shortest zone is 38' and only capable of emitting (600 x 38' =) 22, 800 BTU/hr, which less than 1/4 of the boiler output.
Even the longest zone is only 60', and only capable of emitting ~36,000 BTU/hr which is barely over 1/3 of the boiler output.
When serving any one zone the thing will short-cycle like crazy, and unless three zones (say, the 60' + 55' + 40' zones) are simultaneously calling for heat the thing is going to be doing a lot of on/off burn cycling during continuous calls for heat. This puts lot of wear & tear on the boiler, and cuts significantly into it's operational efficiency. With the higher frequency of startup cycling losses and low burn durations it is unlikely to be performing anywhere near it's stated AFUE numbers. Even with the three zones tied to gether it's only good for emitting ~93K, not the full 101K, but the thermal mass of the boiler & system water is high enough that it will still have decent burn lengths, with very few cycles per hour.
Only with
all four zones calling for heat at once can the radiation can actually balance the full boiler output, settling in at an average water temp of about 170F.
Retrofitting a heat purging economizer control like the Intellicon 3250 or similar onto the boiler, bypassing it's aquastats can probably cut the the number of burn cycles in half to help some- might even save 15% on the fuel use, but it would be better to combine some zones as well. Since the basement load is probably comparatively low it's fine to let it short cycle on that one a bit for those times that you turn it on, but for the rest of house it's better for the oversized boiler to run it all as a single zone, provided that can be done with reasonable room-to-room temperature balance.
Longer term it's worth thinking about sizing the replacement boiler to the actual heat load of the house. Using mid to late winter gas bills and the
exact meter reading dates, and a ZIP code by which we can
find the nearest weather station for temperature data we can use the boiler as the measuring instrument for figuring out an upper bound for the true heat load. In most cases it will be under 50,000 BTU/hr @ +15F (a typical Long Island
99% outside design temperature) , and it may easily be under 35,000 BTU/hr. (How big, what vintage is this house?)
If the true heat load is under 35K it's possible to keep the zoning as-is if you right-size the boiler for the load, since even the smallest zone's radiation could then emit well over half the boiler's output. A right-sized modulating condensing boiler could do even better, and run nearly continuous burns (even as the zone calls come & go), once you dial in the outdoor reset curves.
If the boiler is fairly new and not likely to be replaced for more than a decade you might get more mileage out of installing a system buffering "reverse indirect" as the hot water heater instead of a standard indirect, slaving the boiler to the indirect's aquastat, and letting the zones sip from the buffering thermal mass of the reverse indirect. With 101,ooo BTU/hr of output you'll never run out of hot water when you do something like this:
From the boiler controls' point of view it's only "zone" is the reverse-indirect. The controls for the other zones only gates the flow of the heating system water out of the buffer tank into the zone calling for heat. Even a 25-30 gallon
Ergomax E23 or
Everhot EA-8-50 would add a couple of minutes to the burns during continuous calls for heat, and can deliver over 120 first-hour gallons when it has a ~100K boiler like the S-120 behind it. It's a bit more expensive than a standard indirect, but it improves the boiler's operating efficiency and reduces wear & tear on the boiler by cutting way down on the number of burn cycles, lengthening the burns.