Sounds like a rather sorry tale. The log novelty has not worn off for me yet, but i have taken to buying them already cut to length…
Thanks David, yes i have seen the pellet burners and they look good, but i’m trying to find a anti frost solution for when we are not there Nov-March.
We are near Royan, and the theory seems to be that the temperature change at certain times over the winter - i.e. from 0-12 degrees in a few hours creates thermic shock which can produce condensation and lead to the pooling of water in the house - so i am trying to create a more stable internal temperature when we are not there. That’s the theory anyway…
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We too are on the west coast (85). When we are away in the winter we use electric heaters in locations where there are water pipes (kitchen, bathroom, cellar, boiler room) set on a frost watch setting, which are also on time clocks so that they only operate at night on the cheap rate electricity tariff. If you have the ‘Heures Creuse / Heures Plein’ tariff then the electricity is 40% cheaper at night. We find the cost to be reasonable and it saves having to drain the water pipes and prevents mould on furnishings.
Pools of water on the floor sounds very unusual and if there is no roof leak indicated by staining on the ceiling, then there must be a lot of damp air entering the building from somewhere.
Do you have a cellar under the house ? If so, then the damp air could well be coming from there. You could fit a plastic damproof membrane to the underside of the cellar ceiling (making sure to tape the joints well), and you could also consider waterproofing the cellar walls and floor (there being several methods to choose from). If there is a internal stairway into a cellar then make sure that there is a close fitting door to stop damp air from coming up into the house.
Clearly there is considerable dampness getting into the house from somewhere, and the best solution is always to find the cause and eradicate it, rather than just trying to suppress the symptoms.
I’ve successfully dealt with a number of different damp problems in various buildings over the years and will be happy to advise you further if you want to PM me.
Install a VMC which will change the air in the house constantly, if correctly set up. It will be much cheaper to run than any form of backgrouind heating.
https://fr.wikipedia.org/wiki/Ventilation_m%C3%A9canique_contr%C3%B4l%C3%A9e
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Like @Robert_Hodge … I think the real reasons WHY a pool of water sits on a wooden floor… and HOW it arrives there… need to be sorted out. 
could simply be wasting time and money… otherwise…
Thanks, Robert, Jonathan & Stella.
There isn’t a cellar and thank you for the offer of further help - i may well take you up on that Robert.
I had heard of the VMC system and it is probably good for the building in any event.
We all agree that it’s the root cause that should be found, the frustration is that it takes a year to test each theory, as it only happens over the winter period when we are not there…
Thanks again.
Last year we experienced a temperature differential from -8 to +15 in less than 24 hours. That was a one off when a cold dry weather system from the North East was replaced by a warm wet one from the South West. I can believe that you see many days below zero around Royan.
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We had a holiday home here before moving over (not too far from the OP) and in the winter left the electric rads on low to keep the house at a certain temperature mainly in case of cold snaps, we never experienced any problems with condensation.
hi I can not help re the heating but is it wise to advertise when your property will be empty?
Absolutely! one house vacant in 17, they will be flocking there 
wasn’t that very pricey? I left mine on NOv - April and the bill was about 300 euro / month. There were 5 set on conf - sun symbol / 1
What did you end up doing? I left my electric rads on low over the winter and was rewarded with an astronomical electric bill.
Last year we experienced mould in the house - dry and green all over the worktops, tables and sofas.
The conclusion was it was the humidity change from winter to a wet spring. Heating would not have resolved that completely. When we arrived in December 2018 we bought a dehumidifier with us, this proved to be very good as on the first day we had 85% humidity, over the course of thee days and emptying the container twice a day, it reduce to around 55% humidity.
We have a converted barn so there is little natural ventilation, it has not been an issue since as we air the house and are here for good (hopefully).
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It is worth getting a dehumidifier that you can connect a drain pipe to so that it can operate when you are not there.
My unit does have that possibility, not required as we live here permanently now, but a must if you intend to plug in and leave.
Ours were set to come on only when the temp dropped to a certain level, it just kept the chill off so when we arrived it wasn’t freezing, old stone houses take a bit of time to warm up.
One of our holiday home clients also hooks up dehumidifiers which empty into the toilets, seems to keep the house free of damp.
My son used to live in an old slate house in North Wales, dehumidifiers going constantly although they lived there permanently.
He gave us his dehumidifier when he moved and it worked beautifully for two days and then it started leaking water from the bottom. I think unless someone was checking regularly I wouldn’t risk leaving a dehumidifier on in an empty house. In one hour we ended up with a bigger problem than we were trying to prevent and the dehumidifier was still operating whilst creating a lake on the floor.
I fitted a rotating cowl to the chimney, and left the log burner door open, this helped a bit, but not perfect. I have bought a VMC kit which i will install before this winter. But we have only been there 2 weeks so far this year.
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