Expand forced air v new elec heat in basement

[hvac rook]

I need help making a decision on a basement heating option.

House: 25 years old, A-frame (lots of windows on front), front faces south and gets loads of passive heat, 1400 sqft + 300 new in basement, basement + 2 floors above. Southern RI - pretty mild due to proximity to the ocean (1 mile) albeit mild for NE. Front room (front half of the house) which gets the passive heat is open to both floors. Due to this the 2 BRs on the second floor are always warm and heat supply here is not critical. No AC, not required.

Furnace detail: Ford Products Corp (no one has heard of this right?) WOH-112/MP-2330, oil-fired, forced air. Central location in basement, original install. Front plenum 12x8 (5x6" takeoffs existing), rear plenum 10x8 (4x6" takeoffs incl. 2 to upstairs). BTU=unknown - can't find anywhere (plate unreadable), but only runs at night or when cloudy and does the job. Single zone control on first floor.

Basement: 2 rooms. 220 sqft rectangle living area and an 80sqft BA/laundry. 2 walls are completely underground. 3 windows and 1 door on other 2 walls. It is built into and on top of a hill. BA is in the corner where 2 walls are completely underground. Will be well insulated and has a 7’ ceiling.

Initial thought was to add 2x6" takeoffs for the living area off the front main to opposite walls (-12") with a return in the middle and 1x6" takeoff for the BA off the rear main. After doing a lot of reading it seems that my air supply may already be maxed out (12x8=440cfm + 10x8=350cfm, ~800 cfm - 9x6"takeoffs @ 100cfm per). This is further supported by the fact that little air comes out of the 2 supplies upstairs (although they are also clearly suffering from losses in the complex duct run to the 2nd floor). I think the burner has the heat in it, but I think the dist system is the limiting factor right now.

1-How does my assessment sound? Am I underestimating the capacity of the furnace/dist system?

2-I am checking out elec baseboard/wall mount (permanent install) as an alternative and need design guidelines:
a-I have seen from 3-15W/sqft for sizing – this is too wide a range, what makes sense for my house? (No load data currently available.)
b-I need advice on fan-coil v radiant heat – is radiant too dependent on the arrangement of room contents to be reliable over the long term?
c-Is this also a better option because it would be too difficult to control temp on all 3 levels with the single zone on the first floor? Obviously, with elec I would have control of the basement separately.

3-General recommendation on a path forward? Go with elec, modify the current system (difficult – limited space), or rip out and install a new furnace with a better dist system (and deal with trying to control temp on 3 levels with a single zone control.

Thanks in advance for any help.

[300 Win Mag]

You will probably need electric baseboard heat even if you add or install new air system, UNLESS you zone the basement seperatly. This is because the basement will get cooler that the rest of the house because of ground effect which is like 50*F, and if your thermostat it upstairs, the heat is not going to come on because it will stay warmer longer upstairs. (especially on a sunny day in spring and fall)

[hvac rook]

Thank you for the response.

[danielworkerbee]

I'd go elec. baseboard with thermostats not on the baseboard.