Can depend on which part of the Herault you live in.
I’m in the Tarn & heat with wood…I have plans for wood fired central heating, but that’s a way off yet.
Insulation can be just as important as the method of heating.
Our house had been done up 14 years ago by the owners at the time.
Apparently he was an electrician. All I can say is the electric heaters may have been good at the time but they are terribly inefficient. We have a woodburner so we can keep the living room cosy and we cope but I really really wish that during their major refurbishment they had put in a decent heating system. I dream about just flicking a switch and being warm.
I’m not far away in Albi where it does freeze. I currently have a woodburner plus oil-fired central heating plus Clim reversible. The oil-fried will come out soon to be replaced with Pompe à chaleur (heat pump) so that may be a good option for youespecially as there are interesting grants available.
If you don’t do it right insulating old walls/homes you can create condensation problems.
One option might be to get a local renewable energy provider to assess the barn, and your proposed layout, to calculate exactly what you need in terms of heat.
But generally more insulation that you ever thought was possible, plus a strategically placed wood burner could do it for you. We have a small 7w woodstove in the gîte that is placed centrally, with an open stairwell to take heat upstairs. In late autumn and early spring (which is prob your sort of winter temp) it heats the whole place 135m2 to a toasty degree.
Surely, it will depend on the layout of the inside.
I know of one barn conversion (rectangular) which has a central living area - open to the roof. The first floor bedrooms and bathrooms are accessed via 2 staircases and an open “corridor” which overlooks the living area on the ground floor.
Anyway, the huge wood burner in the living area heats that area and heat rises (of course) to 2 ceiling fans in the open roof-space, which waft the heat around the first floor to the bedrooms etc all the way round… doors open and the warmth enters.
Having said that, there are small electric radiators for emergency use in all the upper rooms. But, I am told they are rarely needed except in the bathrooms.
Another property has an amazing Tulikivi wood stove which is alight every 3 days in winter.
Their property is elongated rather than 2 stories and the heat does not move about so comfortably despite 2 fans near the stove.