On nothing because it does not yet exist! it was electric convector, a real wound what ...
So the whole installation is to be done.
Also the cheapest is to separate the DHW functions already functional with conserved electricity (good for the summer) and put the wood heating by forced air ducts as I have in one of my houses 60m2, much cheaper than the radiators and sufficient.
The energy to heat the house is much higher than that of domestic hot water and therefore the economy will be very important.
By keeping the convectors as a backup, it is also possible to ensure frost protection by prolonged absence.
After it is always possible to add a water pipe exchanger on the fumes that come out hot to heat a thermal mass and in addition the sanitary water which needs much less power than heating, and which therefore has no no need for a large balloon, 50L is enough given the power of wood heating, while the slow electric balloon requires much more, to keep for the summer, which later can become a solar heating in the summer cheap, like Forhorse did for his horse.
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I tell you an economical solution in investment and free wood that works with me.
Furthermore I get lots of wood for free, logs and hedge trimming, in a quantity much greater than what I have been able to burn over 11 years of windfall since the storm of the end of 1999, so that the results are very interesting, free wood that heats and investment limited to basic insert and circulation ducts of air.
I see wood thrown in a recycling center or burnt in the open air, everywhere in France (smoked by my neighbors !!) both in the Var and in the Paris region, free wood perfect for heating !!
For 3 radiators the central heating is absurd.
While this solution is very economical.