Anyone tried one of these
This is what I discovered:
Every electric heater is 100% efficient, however you want a convection heater when drying plasterer so the heat spreads evenly.
A higher air temperature increases the ability of air to carry (more) water vapour. This is called relative humidity. So if the amount of vapor in the air remains constant, and we increase it's temperature, the RH will drop (ie it will free up capacity in the air for more vapor to occupy).
The water in the plaster will therefore have a greater tendency to leave the plaster and enter the air.
RH can also be lowered by simply extracting the water from the air and this will also free up water vapour capacity in the air again causing the water in the plaster to have a greater tendency to leave and enter the air.
Ideally you would not use a heater at all, just a dehumidifier, because this will not compromise the chemical reaction within the plaster as it sets,
but a heater will reduce the time it takes for the dehumidifier to extract the water out of the plaster. If it's cold like at this time of year go for an oil radiator in the middle of the room. They're cheap, safe, gentle and pretty much all convection. The blowers are okay, but be careful not to force hot air directly at particular areas which could cause them to dry out unevenly leading to cracking or in extreme cases dry out the water before the chemical reaction is complete.