Tim Lamb wrote:

Yes. Actually there is a suspended floor so I am considering installing
a duct terminating next to the hearth. Logistically, any log burner will
only operate while there is somebody to light and feed so early morning
heat will always be gas.

In which case the dhw cylinder will probably be hot before the woodstove is
lit.

Lining the existing chimney looks straight forward as does adapting the
register plate. Where I am struggling is whether to go for room heat
only , graft a 2-3kW gravity back boiler into the existing gas system or
go for something with a wrap around boiler producing 10kW or so but,
presumably, needing much more complication by way of controls.

Its all to do with capital expense, I serviced a log gasifier which heats a
large house, the owner was a timber framing contractor and his wife stoked
the device, it was filled each afternoon and then set itself going at 6:00
the next day, it could be reloaded during the cycle and I think it was
25kW(t), now that's about 7kg of dry wood an hour at 70% efficiency, double
for fresh oak. I wouldn't want to traipse through the house with that much.
It cost GBP20k installed with a heatstore. I doubt I often put more than
4kg/day through my little Jotul (30 years old but relined with bits cut
from broken manhole covers). I haven't plumbed in either of my wood
burners.


I have ground/water source heat pump in mind for a different project.
Air-con is something I have never considered for a domestic use.

An air conditioner is a heat pump when run in reverse, its just air sourced.
Actually they run the same way, just swap the hot end for the cold end of
the circulating fluid I think.

AJH