Gas Boiler - Inadequate Heating - Seeking Feedback/Solution

Hello – As the weather is beginning to get cold in the northeast I realize that I need to finally address a heating problem that we lived with last winter and quickly forgot about as the weather improved. Unfortunately, just like any problem, it is not going to get better by itself. Hopefully, the experts on this site can provide me some guidance.

Problem - Our boiler cannot maintain the indoor temperature above 65F when the outdoor temperature is below the mid-20’s. When the temperature drops to the low-teens, the maximum indoor is in the 60F area. The boiler will nearly run continuously and the boiler output temp never seems to get up to 120F on these cold days, which then doesn’t offer much heat capacity for the baseboards, especially near the end of the loops. This is not a recent issue, the heating system has been inadequate over at least the last few years, but seems to be getting worse.

System overview
• Crown CXE-5 150K BTU “input”, circa 1997, Nat Gas, conventional open combustion, power exhaust via 3” pipe through foundation wall, combustion air from basement (not tightly sealed)
• Four zones, one circ pump
• The aquastat is set at 190 (hi), 10 (diff), no low limit. No ODR.
• Tech inspected recently and found no obvious issues – outdoor temp in upper 50s. No air in system.
• Serviced/cleaned/inspected last fall – no issues except replaced leaking relief valve
• Aquastat replaced two years ago due to failure

House
Two story colonial, unfinished walk out basement, 3800 SF, built in 1998, northern NJ. Two story entry/foyer. 2x4 construction. Medium air-tightness. Bought house in 2006.
Previous owners had large wood stove in FR – might have masked poor performance of heating system. Heat loss calc per Slant/fin app: ~100K BTU. Heavy use of gas fireplace makes heat loss estimate via gas use challenging (seen posters provide analysis using gas bill and degree days).

Zones
(1) indirect hot water (41 gal, Amtrol),
(2) 1st flr (105ft baseboard, 230ft loop), main living area (~2,100 SF)
(3) 2nd flr (63ft baseboard, 200ft loop), 3BR/2Bath
(4) 2nd flr (16ft baseboard, 110t loop) guest BR/laundry (doors typically shut w/ thermostat set at 62F).

Aside from my boiler potentially not operating property my thought is the first floor loop is too long. Includes 30ft of piping in unheated crawl space to supply family rm (350SF). 20ft baseboard. Floor and pipes are insulated. Three exterior walls, over 50% windows, 12ft ceiling, 8-40K BTU sealed gas fireplace.

Potential Solution – Replace boiler with high efficiency model. Add second zone to 1st floor or remove HW baseboard from family room and replace with electric (we primarily heat the FR with a sealed gas fireplace) – would remove 20ft baseboard and 70ft from overall loop. Concern is if we have the FR area on a separate zone, that zone will not run very often and the water in pipes will get very cold. Electronic heat option seems like a sub-optimal solution.

Once again, any insights/suggestions would be greatly appreciated before spending 10K on a new system. I received two quotes last year – neither performed a heat loss calc. If helpful, I can post pics of my system – not sure what items would be of interest.

Thank you.