Position: converting a timber and stone barn to a house, 100mm polyurethane in walls, 140mm in pitched roof, 250mm rock wool in floor, target ventilation rate 0.6 air changes/hr. Fair bit of thermal mass using slate flooring and heraklith in walls. 120m2 floor area. Location on edges of England and Wales nr Ludlow. 2 residents. Off grid, installing a Proven 2.5 soon, estimated average wind speed 4m/s. 2x1m solar water heater [most likely flat panel with 12v PV pump]

Option 1; Underfloor heating running off a wood burning stove with back boiler.
Think we need an accumulator and pumps - concerned that pumps may require too much electricity given we are not on the mains and don't yet know how good a wind site we have here.

Option 2; Pumped radiators running off a wood burning stove with back boiler.
Don't need an accumulator but still need a pump, same concern with electrical requirement.

Option 3; Thermosyphoning radiators running off a wood burning stove with back boiler.
No pumps required but due to restrictions on all pipes [min 28mm copper] needing to rise along their entire length from boiler to radiators it is not possible to have radiators in some rooms without pipes crossing in front of windows a few feet up and having a couple of radiators half way up the walls..

Option 4; Two wood burning stoves without radiators [well one would have a back boiler for heating domestic hot water and would have a radiator for pressure relief]
Nice and simple to install but will the heat percolate through the rooms enough? Building regs require us to put sound insulation in the internal walls and we are worried that this could prevent heat moving from heated rooms to unheated rooms.

Any comments/ suggestions very gratefully received!

tony - Surely MHVR off grid is a non starter?

It sounds like quite a challenge - is it a single floor building, and how many rooms? I'd possibly consider two stoves and then start to work on ways to get the heat around... you could have a stove in one room and route the stack up through another, or back boiler plus a small rad in the room behind etc.

As it's only two residents, you might get a lot of mileage out of designing the room layout to suit more localised heating - say a open plan living/eating/cooking area and a seperate sleeping zone.

And it won't need full speed all the time either.

Depends if you want heating on demand or if you are prepared to get up a few times a night to keep the woodburners in?

If not you are into multi fuel burners using coal/anthracite which is of course not good.

If you are going for relatively airtight build then some form of mechnical ventilation is required.
Most MVHR suppliers have a range of models, some with low electrical consumption which are obviously a bit pricier.
If you have Solar HW you will be needing a tank so why not combine the wood stove and solar into a decent sized thermal store which will only require a periodic burn to get the store up to temperature.
What sort of electric consumption do pumps have? Wouldn't have thought it was outside the capability of an off grid system???