Thanks a lot for the detailed reply. Old radiators operate in high temperature but from what I understand, the fan coil heaters operate in lower temperature more equivalent to radiant floor heating.
For cost reasons, installing undefloor heating is not an option, that's why I opted for low temp radiators on top of floor. However, it sounds like the heat pump system will not be cheap either. According to BTU calculator I found online, seems like I need 28K BTUs to heat the home. I thought about pellet burners as well, but here in Europe, the cost of pellets has sky rocketed this year. I don't want to be dependent on gas either, also electricity is not cheap... So I am not sure exactly what i'll go with. I'll do the calculation, but your input on the effectiveness of the theromosiphon system is valuable, thank you.
A "variable speed compressor" is what you want in a heat pump, as these modulate their speed (and electricity usage) to produce a constant amount of heat. You might be okay with a 24K BTU system, especially when coupled with the thermosiphon and then some effort spent on insulation & air-sealing?
Here in the US the base system would be about $3K USD, but with installation costs on top of that.
For cost reasons, installing undefloor heating is not an option, that's why I opted for low temp radiators on top of floor. However, it sounds like the heat pump system will not be cheap either. According to BTU calculator I found online, seems like I need 28K BTUs to heat the home. I thought about pellet burners as well, but here in Europe, the cost of pellets has sky rocketed this year. I don't want to be dependent on gas either, also electricity is not cheap... So I am not sure exactly what i'll go with. I'll do the calculation, but your input on the effectiveness of the theromosiphon system is valuable, thank you.