I use a 72kW one at work for a big building..
I have similar style house, currently has has has Gas CH, wood stoves and solar panels.
all helps, but the most important part was insulation.
as I redid rooms i stripped the lath and plaster and popped in 100mm kingspan, put ROCKWOOL slabs under the suspended timber floor and between some ground floor/first floor ceiling voids to top up the Victorian deafening.
i enjoy modernising the house